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ABSTRACT

The Cincinnati Arch region of Ohio, Kentucky, and Indiana is an icon of North American Paleozoic stratigraphy, as it exposes strata ranging from Ordovician to Pennsylvanian in age. In particular, the highly fossiliferous Ordovician, Silurian, and Middle Devonian successions have been extensively studied since the nineteenth century, and continue to serve as a crucial proving ground for new methods and models of biostratigraphy, chemostratigraphy, and sequence stratigraphy in mixed clasticcarbonate depositional settings. These strata are locally capped by Middle Devonian limestones with their own diverse fauna and unique depositional history. Outcrops near Louisville, Kentucky, provide an excellent opportunity to examine these strata firsthand and discuss sequence stratigraphy, chemostratigraphy, sedimentary environments, and paleoecology. A series of new roadcuts south of Mount Washington, Kentucky, exposes the lower to middle Richmondian Stage (Upper Ordovician, Cincinnatian) and presents a diverse suite of marine facies, from peritidal mudstones to offshore shoals, coral biostromes, and subtidal shales. These exposures are well suited for highlighting the revised sequence stratigraphy of the Cincinnatian Series, presented herein. Nearby outcrops also include much of the local Silurian succession, allowing an in-depth observation of Llandovery and Wenlock strata, including several chemostratigraphically important intervals that have improved regional and international correlation. Supplementary exposures east and north of Louisville provide context for subjacent and superjacent Ordovician-Silurian strata, as well as examples of lateral facies changes and unconformities. Additionally, the Falls of the Ohio at Clarksville, Indiana, features an exceptional outcrop of the overlying Middle Devonian succession, including an extensive and well-preserved biostrome of corals, sponges, and other marine fauna. These fossil beds, coupled with significant exposures in local quarries, are critical for understanding the paleoecology and stratigraphy of the Middle Devonian of the North American midcontinent.

INTRODUCTION

Litho-, bio-, and taphofacies are not randomly distributed in rocks. Rather, the chemical and physical processes governing sediment accumulation, as well as ecological distribution and fossil preservation are predictably linked to aspects of changing environment and sedimentation patterns. Sequence stratigraphy provides a heuristic model that links physical processes with predictable changes in the distribution of facies, biotas, and discontinuities (Brett, 1995, 1998; Witzke et al., 1996; Holland and Patzkowsky, 1996, 2007).

In this paper, we will explore aspects of fossil distribution, bioevents, and taphonomy in relation to depositional processes in mixed siliciclastic-carbonate sequences of the classic lower and middle Paleozoic on the western flank of the Cincinnati Arch. We will demonstrate some predictable aspects of the sedimentological and paleontological record related to sequence stratigraphy and depositional environments. In addition, we will consider numerous remaining problems of biostratigraphy, taphonomy, and the paleontology of bioevents.

Louisville, Kentucky, and surrounding communities owe their very existence to the local bedrock, as the region was originally settled, in part, as a portage for river transportation around rapids on the Ohio River. This whitewater was caused by a minor anticline elevating resistant beds of Silurian and Devonian limestone. Here the river dropped ~8 m in 4 km, the strongest gradient along its 1579 km course. Today the course of the Ohio River has been reshaped and rerouted with dynamite, dams, locks, levees, and floodwalls; barges now float by placidly, unperturbed by the geology. However, much of the underlying strata that once formed the bed of the rapids has been preserved at the Falls of the Ohio, now an Indiana State Park. Readily accessible and tremendously fossiliferous, this section is primarily composed of the Middle Devonian Jeffersonville Limestone and has been extensively studied and documented (Conkin and Conkin, 1972, 1976, 1980; Greb et al., 1993; Hendricks et al., 1994; Powell, 1999; Goldstein et al., 2009; also see section by Bulinski, herein).

The regional geology of Louisville is not limited to Devonian strata. The city is near the border of the intracratonic Illinois Basin and the western flank of the Cincinnati Arch (Fig. 1), which dips gently (less than 0.5°) to the west. The arch, regionally situated on a major basement suture zone along the Mesoproterozoic Grenville front, is a long-lived positive structure that appears to have existed in various forms through much of the late Paleozoic (Root and Onasch, 1999). The most recent iteration was formed as a forebulge resulting from the Alleghanian orogeny (Ettensohn, 1992a, 1992b, 2008). This uplift and subsequent erosion exposed strata ranging from Upper Ordovician (Katian; Cincinnatian) east of Louisville to Mississippian and even Lower Pennsylvanian units in plateaus to the east and west.

Figure 1.

Regional geology of the U.S. Midcontinent showing major structural features. The Louisville field-trip area (rectangle) lies at the boundary between the Illinois Basin and the Cincinnati Arch. IL—Illinois; IN—Indiana; KY—Kentucky; MI—Michigan; OH—Ohio; ON—Ontario; PA—Pennsylvania; VA—Virginia; WI—Wisconsin; WV—West Virginia.

Figure 1.

Regional geology of the U.S. Midcontinent showing major structural features. The Louisville field-trip area (rectangle) lies at the boundary between the Illinois Basin and the Cincinnati Arch. IL—Illinois; IN—Indiana; KY—Kentucky; MI—Michigan; OH—Ohio; ON—Ontario; PA—Pennsylvania; VA—Virginia; WI—Wisconsin; WV—West Virginia.

The Upper Ordovician (Katian; Cincinnatian), Silurian (Llandovery–lower Ludlow), and Middle Devonian (Eifelian–Givetian) intervals form the focus of this guide. While these strata are exposed along local streams and rivers, the modern stratigraphic renaissance largely owes its existence to the numerous fresh roadcuts and quarries that characterize the Louisville region (see Conkin, 2002; Conkin et al., 2004a, 2004b, 2006). These exposures provide easy access to an exceptional composite section through multiple mixed siliciclastic-carbonate successions. Furthermore, the outcrop region covers hundreds of square kilometers, providing the opportunity to observe facies changes and other trends over space as well as time.

GEOLOGICAL SETTING

Lower to Middle Paleozoic strata near Louisville are dominated by limestones and dolostones, punctuated by relatively thin yet geographically widespread shale packages, some of which are locally fossiliferous. These mixed carbonate and siliciclastic sediments accumulated in a shallow epicontinental sea that once covered much of the paleocontinent of Laurentia, the ancient core of North America. To the east lay the Appalachian Basin; to the west, an extensive carbonate ramp sloped gently into the Illinois Basin (Fig. 1). During the time interval covered in this field guide—Late Ordovician to Middle Devonian, roughly 70 million years (450–380 Ma)—the field-trip area lay predominantly in the southern subtropics. Laurentia is believed to have been at ~20–23° south latitude in the Late Ordovician (MacNiocaill et al., 1997; but see Swanson-Hysell and Macdonald, 2017, for a lower latitude, maybe even equatorial, interpretation) and perhaps at 35–40° south by Early Devonian time (Scotese, 2001). This was followed by rather rapid northward drift of the craton during the Carboniferous. Thus, the region lay within the subtropical hurricane-dominated belt throughout the Late Ordovician to Middle Devonian. Climates during this interval were predominately warm and ranged from humid to arid. Cool water conditions, such as those concurrent with the end Ordovician (Hirnantian) to early Silurian (Rhuddanian) “ice house” (Finnegan et al., 2011), are not well represented, in part due to their association with eustatic lowstands. However, certain intervals in the Silurian may record cooler water facies (Thomka, 2015).

Beginning in the Late Ordovician, the local climate may have been intermittently semi-arid and the region was prone to hypersalinity during the late Silurian. Major evaporite deposits accumulated nearby in the Michigan Basin and northern Appalachian Basin. Similarly, during the Middle Devonian, sabkha facies were developed in the northern Wabash platform. This tendency toward hypersalinity may have strongly influenced organism distribution.

Maximum water depths were probably only a few tens of meters, and locally may have been significantly shallower. Horizons recording peritidal features such as desiccation cracks, “verdine facies” (Odin, 1988), and possible tidally produced sedimentary structures, are common in several units (e.g., the Upper Ordovician Saluda Member of the Whitewater Formation). Likewise, widespread “shoal” facies, comprising pelmatozoan grainstones (e.g., the lower Silurian Brassfield Formation) and/or oolitic limestones, suggest high-energy, shallow water conditions (Gordon and Ettensohn, 1984). However, most of the succession represents shallow shelf sedimentation below normal (but above storm) wave base (Brett et al., 1993, 2015a; Brett and Ray, 2005). The identification of distinctive assemblages of microendoliths produced by photoautotrophic algae and cyanobacteria in Upper Ordovician (Richmondian) beds indicates deposition in predominantly shallow euphotic successions (Vogel and Brett, 2009; Brett et al., 2015a). Brachiopod assemblages are typically identifiable as benthic assemblage (BA)-2 to BA-4 (Boucot, 1975; Boucot and Lawson, 1999), interpreted as depths of ~5-50 m (Brett et al., 1993).

Topography of the local sea floor was variably influenced by far-field tectonics associated with local crustal flexure and movement along deep-seated basement faults (Ettensohn, 1992a, 1994). During the Late Ordovician, the Lexington platform extended from the Kentucky-Indiana border region in the west to the Taconic foreland basin in the east. A localized structural high developed in the area from Frankfort to Winchester, Kentucky. Upwarping of this region may reflect the presence of isolated fault blocks resulting from the intersection of two major fault systems, the Iapetan Kentucky River fault system and the Lexington fault zone, localized along part of the Proterozoic Grenville front (Ettensohn, 1991, 1992b). Likewise, the Taconic collision appears to have reactivated old zones of structural weakness, producing subsiding regions both north and south of the Lexington platform. The Sebree trough, a relatively narrow (tens of kilometers wide) northeast-southwest-trending basin crossing through western Ohio, southeastern Indiana, and western Kentucky, formed a locus of deeper water sedimentation during the Chatfieldian to early Cincinnatian interval (early Katian). This trough was an under-filled basin that accumulated dark shales and thin allodapic carbonates synchronously with the production of shallow water shoal facies in the Lexington platform. However, the Sebree was largely infilled with fine-grained siliciclastics (mainly black and dark-gray graptolite-bearing shale) by Maysvillian time.

In general, the local background sedimentation was dominated by carbonate deposition, often accumulated as lime mud and silt (micrite) in relatively calm water environments. However, storm effects, such as graded bedding and erosion surfaces with intraclasts, are widely evident, especially in Ordovician strata (Jennette and Pryor, 1993; Dattilo et al., 2012). Still, the widespread persistence and complexity of shell beds in many muddy successions indicate that while storms mediated the development of these beds, their principal cause may have been periods of basin-wide sediment starvation associated with climatic change and/or sea-level rise (Brett et al., 2008b; Dattilo et al., 2008, 2012).

In many Silurian successions, such as the Laurel and Louisville formations, these carbonates show alternating horizons of heavily burrow mottled, sparsely fossiliferous lime mudstone (wackestone fabrics). Thalassinoides burrow galleries in the beds may be accentuated by local rusty weathering dolomite and/or chert (Sheehan and Schiefelbein, 1984; Watkins and Coorough, 1997), the latter probably locally sourced from siliceous organisms such as sponges. (However, note that non-biogenic chert is well known from lower Upper Ordovician strata in central Kentucky, co-occurring with many K-bentonite ash beds; see Brett et al., 2018a, for examples in the Tyrone Formation.)

Although these intrabasinal carbonates form the primary sediment, thin, sheet-like, mudstone-dominated packages are very widespread through much of the Ordovician–Devonian. These include parts of the trilobite-rich “butter shales” of the Cincinnatian (Aucoin et al., 2015, 2016) and the Silurian-age Massie and Waldron shales. Such intervals show evidence of episodes of relatively abrupt input of siliciclastic muds into the basin. The source areas for these major sediment influxes were almost certainly the eastern orogens: the Taconic in the Middle to Late Ordovician (Ettensohn, 1991; Fitzgerald, 2016), the Acadian in the Devonian (Ettensohn, 1985, 1987, 2004), and the Alleghanian in the Carboniferous (Gray and Zeitler, 1997). However, the processes responsible for deposition of widespread mudstones remain somewhat enigmatic. Certain beds were likely the result of broadly dispersed plumes of fine-grained sediments, spread on the sea surface or along internal boundary surfaces (Aucoin et al., 2016). These pulses possibly followed extreme flooding events, oversized storms, or tsunamis, which produced mass inundation and offshore-directed hyperpycnal sediment flows. Fossil taphonomy shows that some of these mud deposition events were very rapid indeed, literally burying benthic organisms alive in regional obrution deposits resulting in pristine fossil preservation. However, the larger causes for the thicker packages of shale remain poorly resolved. They appear to be associated with (or following) eustatic highstands and/or tectonic pulses that delivered significant amounts of siliciclastic debris to the basin (Aucoin et al., 2016).

SEQUENCE AND CYCLE STRATIGRAPHY

The Upper Ordovician to Middle Devonian strata exposed in the Cincinnati Arch and adjacent regions are divisible into a series of small- or meter-scale cycles (0.5–2 m thick, perhaps representing a few tens of thousands of years; 5th- and 6th-order), medium-scale cyclothems (3–10 m thick, representing hundreds of thousands of years; 4th-order), and large-scale sequences (typically 10–100 m, ranging from 0.5 to 5 million years in duration; 3rd order) (Coe, 2005; Embry, 2009, Catuneanu, 2006; Figs. 2, 3). These are interpreted in the context of sequence stratigraphy, following general concepts outlined by Sloss (1963, 1988), Vail et al. (1977), Van Wagoner et al. (1990), Van Wagoner and Bertram (1995), and more recently updated in Coe (2005) and Catuneanu (2006). While the widespread nature of many depositional sequences is typically attributable to eustatic processes (Catuneanu, 2006) the larger scale 2nd- and 3rd-order sequences may have a tectonic origin or may be strongly modified by regional tectonics (Ettensohn, 1994, 2004).

Figure 2.

Comparison of idealized stratigraphic motifs of 3rd-, 4th-, and 5th-order cycles for mixed carbonate-siliciclastic cratonic ramp successions. Note many analogous aspects of sequence patterns across scales. Abbreviations: ETST—early transgressive systems tract; FRS—forced regression surface; FSST—falling stage systems tract; HST—highstand systems tract; LST—lowstand systems tract; LTST—late transgressive systems tract; MFS—maximum flooding surface; MSS—maximum starvation surface; SB—sequence boundary; TST—transgressive systems tract. MSS contacts are marked by mineralized corrosion surfaces or hardgrounds. Modified from McLaughlin et al. (2008b).

Figure 2.

Comparison of idealized stratigraphic motifs of 3rd-, 4th-, and 5th-order cycles for mixed carbonate-siliciclastic cratonic ramp successions. Note many analogous aspects of sequence patterns across scales. Abbreviations: ETST—early transgressive systems tract; FRS—forced regression surface; FSST—falling stage systems tract; HST—highstand systems tract; LST—lowstand systems tract; LTST—late transgressive systems tract; MFS—maximum flooding surface; MSS—maximum starvation surface; SB—sequence boundary; TST—transgressive systems tract. MSS contacts are marked by mineralized corrosion surfaces or hardgrounds. Modified from McLaughlin et al. (2008b).

Figure 3.

Idealized stratigraphic column of the Ordovician, Silurian, and Devonian succession in the region of Louisville, Kentucky. Note that the Wabash Formation, represented north of the Ohio River, is apparently absent at Louisville. Abbreviations: Lland.—Llandovery; Mays.—Maysvillian. Sequence designations based on Brett et al. (2018a) for the Ordovician; Brett et al. (1990) and Brett and Ray (2005) for the Silurian; and Brett et al. (2011) for the Devonian. Basic figure adapted from Conkin et al. (1992b).

Figure 3.

Idealized stratigraphic column of the Ordovician, Silurian, and Devonian succession in the region of Louisville, Kentucky. Note that the Wabash Formation, represented north of the Ohio River, is apparently absent at Louisville. Abbreviations: Lland.—Llandovery; Mays.—Maysvillian. Sequence designations based on Brett et al. (2018a) for the Ordovician; Brett et al. (1990) and Brett and Ray (2005) for the Silurian; and Brett et al. (2011) for the Devonian. Basic figure adapted from Conkin et al. (1992b).

Each depositional sequence commences with a sharp, typically nearly planar erosion surface known as a sequence boundary (SB; Fig. 2). In many cases, this surface demonstrably truncates subjacent strata forming a regionally (i.e., manifest over tens of kilometers) angular unconformity. Some of the unconformities present in the Louisville area (e.g., the Cherokee, Wallbridge, and Taghanic unconformities) are major megasequence bounding surfaces with several million years unrepresented (Sloss, 1963, 1988; Dennison and Head, 1975). These large gaps record both far-field tectonic (epeirogenic uplift and subsidence) and large-scale eustatic lowstand erosion effects, which produced extended periods of exposure, karst, and erosion. Counterintuitively, the most significant unconformities can also be the least remarkable, manifest as “peneplain” style surfaces devoid of relief or topography. For example, the Wallbridge unconformity (Louisville paraconformity) that omits some 30 million years of late Silurian and Early Devonian time—an interval longer than the entire Silurian Period—often appears as a simple bedding plane.

Many of these disconformities are composite surfaces; they reflect the convergence of multiple separate unconformities onto relatively positive areas associated with the inner platform and/or forebulges (see McLaughlin and Brett, 2004, 2007; Brett and Ray, 2005). In many cases, when the disconformity is minor, the surface displays a sharp contact between deeper and shallower water facies, i.e., facies dislocation. Most disconformities are erosion/transgression (E/T) surfaces, i.e., combined lowstand erosion surfaces and transgressive ravinement (shoreface erosion) surfaces; in most cases, the latter have likely erased any record of subaerial exposure (but see Brett et al., 2014, for an example of preserved karst surfaces). Similarly, the record of true lowstands is typically absent in this setting.

Transgressive systems tracts (TSTs) in mixed siliciclastic-carbonate successions are typified by compact skeletal packstones or grainstones and rudstones, a few meters thick, sometimes with stacked burrowed firmgrounds or hardgrounds. Such beds are typically enriched in stenotopic benthic taxa, such as corals, bryozoans, stromatoporoids, and large crinoids. In deeper siliciclastic-dominated successions, such as the Devonian New Albany Shale (Fig. 3), TSTs are minimally developed. Within such successions, the sequence boundary, transgressive surface, and maximum flooding (starvation) surfaces are very nearly juxtaposed. Highly condensed TSTs are represented only by thin (mm to a few cm) lag beds of reworked phosphatic nodules, pyrite, fish bones, crinoid ossicles, and/or glauconite (Brett et al., 2003b).

A second type of surface, easily identified in most middle Paleozoic sequences on the Cincinnati Arch, is a sharp contact between compact, usually skeletal carbonates and overlying shaly, nodular carbonates or shales reflecting low-energy, deeper water facies (Brett et al., 2015a; McLaughlin et al., 2004, 2008a). These surfaces are commonly marked by hardgrounds with phosphatic or pyritic crusts, shelly lags, or corrosion of older carbonates (McLaughlin and Brett, 2007; McLaughlin et al., 2008a). In many cases, there is evidence for further back-stepping of minor cycles above these surfaces in the late transgression to early high-stand. Hence, they do not represent the true end of the TST but rather a maximum sediment starvation surface (also known as a surface of maximum starvation or MSS; Brett, 1995; Brett et al., 2011; McLaughlin et al., 2004; Fig. 2). These probably formed during the time of maximum rate of sea-level rise, sequestering of siliciclastics in the nearshore areas, and drowning of carbonate platforms. Interestingly, biostromes or small bioherms are typical of these intervals.

Highstand systems tracts (HSTs; Fig. 2) are typified by deep, offshore successions that show some tendency to shallow upward from deepest facies near their bases. Highstands may be characterized by relatively thick pure claystone or mudstone deposits including the so-called butter shales, which though sparsely fossiliferous may yield spectacularly preserved trilobites and mollusks (Aucoin et al., 2015, 2016). For pure carbonates, HSTs may be recorded in thinly bedded skeletal hash and micritic limestone beds or simply as fine-grained, tabular silty dolomicrites typically with abundant bioturbation, especially Thalassinoides (Sheehan and Schiefelbein, 1984) and firmground horizons that may be accentuated by layers of chert nodules. In mixed siliciclastic carbonate sequences, they may be very shaly nodular carbonates, although erosion at disconformities often produces a stacking of early transgressive successions upon one another with limited preservation of later highstand phases. In deep offshore facies such as the New Albany, HSTs are mainly black shales, generally with knife-sharp boundaries that reflect maximum sediment starvation and/or maximum flooding surfaces (Schieber and Lazar, 2004).

A third type of surface, developed in some but not all sequences, is a somewhat irregular to channelized surface overlain by sandy skeletal carbonates (calcarenites), laminated calcisiltites, and, in some cases, quartz siltstones. These erosive surfaces are not sequence boundaries, as they do not show evidence of subaerial exposure nor major regional truncation, and they can lie well below identifiable sequence boundaries. Overlying beds are typically sparsely fossiliferous except for highly abraded/corroded skeletal grains, though widely scattered, well-preserved fossils may occur. Such intervals are interpreted as falling stage (forced regressive) systems tracts (FSST; Fig. 2); their sharp basal surfaces are marine erosion surfaces associated with forced regression that focused wave and current erosion on the sea floor. They may often yield discrete, well-preserved ichnofossils such as escape traces, Planolites, Skolithos, and others. In Devonian and younger successions, silty beds are typically rich in Zoophycos; however, these traces have not been identified in the older sediments of the Cincinnati Arch region. Synsedimentary deformation is also especially typical of these FSST packages and may include intervals of ball-and-pillow deformation, broken and rotated slabs, synsedimentary slumping, mud diapirs, and flame structures (McLaughlin and Brett, 2004; Brett et al., 2008a). These are interpreted as seismically induced deformation related to foundering and minor slumping on slightly steepened ramps (Pope et al., 1997; McLaughlin and Brett, 2004; Ettensohn et al., 2002; Jewell and Ettensohn, 2004). The mixture of rapidly deposited carbonate/clastic silts and interbedded thixotropic muds may have made these intervals especially prone to deformation during seismic shocking from local movement along basement faults associated with far-field tectonic stresses. Deformed beds are commonly cut by sequence boundaries.

Recent research has emphasized the use of principles of sequence stratigraphy to classify depositional packages in local strata into a series of numbered sequences that can be correlated eastward into the Appalachian Basin, where they become nearly conformable, although the larger facies dislocations can still be identified as successions become increasingly conformable (Brett and Ray, 2005; Brett et al., 2011). For example, Holland (1993) and Holland and Patzkowsky (1996, 2007) subdivided the Cincinnatian succession into a series of six depositional sequences labeled C1 to C6; these correspond roughly to some of the previously recognized lithostratigraphic units. Recent study by the authors and our colleagues has been directed toward clarification and refinement of this well-established and widely used schema and has revealed the need for critical revisions. For example, study of the Maysvillian (mid-Katian) strata by Schramm (2011) and Malgieri (2015) and Richmondian (upper Katian) strata by Aucoin (2014) and Schwalbach (2017) identified previously undescribed sequence boundaries within Holland and Patzkowsky’s (1996) 3rd-order sequences and reclassified strata into a total of eight sequences (C1 through C8); these are considered to represent 3rd-order sequences on the basis of estimated durations (>0.5 Ma), and because each shows demonstrable regional truncation beneath their basal sequence boundaries. These eight sequences subdivide into 4th-order sequences (Brett et al., 2018a).

Similarly, the Silurian and Devonian 3rd-order sequences identified in Ontario, New York, and the central Appalachians (e.g., Brett et al., 1990, 1998, 2011) have been extended into the cratonic successions of the Cincinnati Arch (Brett and Ray, 2005; McLaughlin et al., 2008b; Sullivan and Brett, 2013; Sullivan et al., 2014, 2016). In both the Silurian and Devonian, what is preserved on the proto-Cincinnati Arch largely constitutes a stacking of the transgressive to early highstand carbonates, with much of the shaly highstands removed by erosion beneath the next successive sequence boundary. Thus, the concept of “TST-stacking” (Brett, 1995) is particularly well demonstrated in these strata.

These large- and medium-scale cycles (3rd- and 4th-order sequences of Catuneanu, 2006, and Embry, 2009) provide useful approximate chronostratigraphic units, and their widespread distribution across cratonic and foreland basin successions strongly implicates a eustatic origin. However, local thickening, especially in areas of minor structural basins and monoclines, and enhanced erosion at local arches, demonstrates the importance of far-field tectonics during the Ordovician Taconic and Silurian-Devonian Salinic-Acadian orogenies (Ettensohn, 1992b, 2008; Ettensohn and Brett, 2002). Depocenters and minor arches were not stationary—they were dynamic features that shifted through time, probably through variable uplift and subsidence of crustal blocks separated by reactivated basement faults (e.g., Root, 1996), as eastern Laurentia responded to changing stresses during numerous orogenic phases. High-resolution regional surface and subsurface mapping of chronostratigraphically precise units (e.g., Waid, 2018a) is necessary to fully understand the complex interplay between eustatic and regional, tectonically driven changes in depositional environment.

Many of the larger depositional sequences preserve internal frameworks of smaller, meter-scale cycles, and certain intervals show distinctive patterns of rhythmic bedding that appear to represent a diagenetic overprint of carbonate redistribution on primary cycles. Most of these occur in the late highstands of sequences when conditions in the interior seaway were positioned between carbonate and siliciclastic clay deposition. We have noted that distinct patterns of alternating carbonates and shales can be traced over vast distances. Consequently, we suggest that these rhythmic bedding patterns reflect climate oscillations that may have resulted in alternating periods of clastic sedimentation or starvation, coupled with relative decreases and increases in local carbonate production. Further study of astrochronology of these small-scale cycles is revolutionizing chronostratigraphy in many parts of the stratigraphic column.

BIOSTRATIGRAPHY AND CHEMOSTRATIGRAPHY

Relatively new stratigraphic techniques such as magnetic susceptibility and stable carbon isotope chemostratigraphy can provide valuable paleoclimate information. Furthermore, when coupled with biostratigraphy, these techniques can further refine chronostratigraphic correlations, sometimes to precisions of ca. 500 k.y. (e.g., Cramer et al., 2010a, 2010b, 2015). These approaches have been widely applied in recent years, but textbook examples are well represented in the Cincinnati Arch region and deserve further note.

Local biostratigraphic research is largely focused on conodonts, as graptolites are lacking in most carbonate units and only rarely found in certain shales (notably the Upper Ordovician Kope Formation). The Upper Ordovician of the Louisville area may be assigned to the Amorphognathus superbus (middle Chatfieldian to lowest Richmondian) and A. ordovicicus (lower Richmondian and above) North Atlantic conodont zones, with the zonal boundary high in the Arnheim Formation (Goldman and Bergström, 1997; Fig. 4). These conodont zones correlate to the Amplexograptus manitoulinensis (upper Maysvillian to middle Richmondian) and Dicellograptus complanatus (upper Richmondian) graptolite zones, although to our knowledge zonally significant graptolites have not been reported from the field-trip area.

Figure 4.

Schematic north to south time-rock diagram of the Upper Ordovician (Cincinnatian) sequence stratigraphy of the western Cincinnati Arch, using the revised sequence stratigraphic nomenclature of Brett et al. (2018a). Colors signify a combination of systems tracts and facies (see legend at top of figure). If not otherwise designated, the unit names refer to member-scale divisions of Cincinnatian strata. A.—Amorphognathus; FSST—falling stage systems tract; HST—highstand systems tract; TST—transgressive systems tract.

Figure 4.

Schematic north to south time-rock diagram of the Upper Ordovician (Cincinnatian) sequence stratigraphy of the western Cincinnati Arch, using the revised sequence stratigraphic nomenclature of Brett et al. (2018a). Colors signify a combination of systems tracts and facies (see legend at top of figure). If not otherwise designated, the unit names refer to member-scale divisions of Cincinnatian strata. A.—Amorphognathus; FSST—falling stage systems tract; HST—highstand systems tract; TST—transgressive systems tract.

Global Silurian conodont biozonation has been updated considerably since the classic regional studies by Rexroad (1967, 1980), Rexroad et al. (1965), Nicoll and Rexroad (1968), Rexroad and Kleffner (1984) and Kleffner and Ausich (1988). Precise biozonations based on Baltic conodont faunas, developed by Jeppsson (1997) and Männik (1998, 2007), have greatly increased the chronostratigraphic precision of Silurian correlations. Kleffner (in McLaughlin et al., 2008b, and Kleffner et al., 2012), has made substantial progress in refining the conodont zonation of Silurian rocks along the Cincinnati Arch by updating the classic conodont studies into the modern zonations, and through additional specimen collection.

Analyzing the stable isotope chemostratigraphy of these successions is another major boon to the understanding of correlations and global environmental processes. The ratio of 13C to 12C in carbonate rocks (δ13Ccarb) follows the ratio in seawater at the time of deposition. Well-mixed oceans with respect to these isotopes result in patterns of δ13Ccarb that form reliable chronostratigraphic markers (Saltzman and Thomas, 2012). Despite dolomitization and other diagenetic effects, stable carbonate carbon isotopes yield relatively consistent patterns in sections already roughly correlated via independent means (Glumac and Walker, 1998). The generation of δ13Ccarb data for numerous intervals widespread across different paleocontinents has led to the identification of distinctive negative and positive δ13Ccarb excursions of global extent (Saltzman and Thomas, 2012). These excursions appear to be related to changes in the global carbon cycle. The rapid burial of organic matter in the global oceans can lead to correspondingly rapid increases in δ13Ccarb values in carbonates (Kump and Arthur, 1999).

Work pioneered by Bergström et al. (2010a, 2010b) is leading to a standardized isotopic curve for the Upper Ordovician (Mohawkian and Cincinnatian; uppermost Sandbian and Katian) strata of the Cincinnati Arch and beyond. These studies identify major positive δ13Ccarb excursions such as the Guttenberg (GICE), Kope, Fairview, Waynesville, Whitewater, and Elkhorn (the latter five named for classic Cincinnatian formations). An additional excursion, the HICE, is characteristic of the terminal Ordovician Hirnantian Stage.

In like manner, Silurian studies by Cramer and Saltzman (2005, 2007); Cramer et al. (2006a, 2006b, 2010a, 2010b, 2011), McLaughlin et al. (2008b, 2018), and Sullivan et al. (2014, 2016) have enabled identification of the Telychian Valgu, the Sheinwoodian Ireviken, the Homerian Mulde, and the major Ludfordian Lau positive δ13Ccarb excursions. Even more minor shifts in the δ13Ccarb data, such as a widespread early Sheinwoodian negative shift (Cramer, 2009; Cramer et al., 2010a, 2010b; McLaughlin et al., 2012), may be identifiable within these rocks.

Several important δ13Ccarb excursions and associated bioevents have been identified in Devonian rocks of equivalent age to those exposed in the Falls of the Ohio area, including positive excursions in the earliest Eifelian (Chotec Event), the late Eifelian (Bakoven Event), earliest Givetian (Kačák Event) and late Givetian to early Frasnian (Taghanic and Frasnes events) (see Becker et al., 2012, for a summary). Unfortunately, to date, little chemostratigraphic work has been done on the Devonian strata of the Falls of the Ohio area itself; this would clearly be a useful addition and might help to clarify some correlations.

REGIONAL STRATIGRAPHY

Situated on the western flank of the Cincinnati Arch, the greater Louisville metropolitan area overlaps the Ordovician, Silurian, Devonian, and Mississippian outcrop belts. A summary of Upper Ordovician to Middle Devonian stratigraphic units relevant to the field-trip area is presented here, organized in ascending order by geologic period and depositional sequence (Fig. 3).

A brief forenote on stratigraphic nomenclature is warranted. Because the study region is on the Kentucky-Indiana border, “state line geology” comes into play: a unit may have one name (and/or rank) on one side of the border, but a completely different name (and/or rank) on the other. For example, the Saluda Member of the Drakes Formation of Kentucky is equivalent to the Upper Ordovician (Richmondian) Saluda Member of the Whitewater Formation in Indiana. Nearby Ohio, with its own historical lexicon for correlative units, also contributes to this confusion (or helps clarify it, depending on one’s philosophical allegiance). Furthermore, these parochial units may differ in their boundaries and vertical extent. For example, the Dillsboro Formation of Indiana encompasses the entirety of the Fairview, Grant Lake, Arnheim, Waynesville, and Liberty formations of Ohio and the Fairview/Calloway Creek, Grant Lake, Bull Fork, and (in part) Drakes formations of Kentucky. Often, these differences are due to lithostratigraphic unit definitions—particularly in the Ordovician, a southeast-northwest-trending paleogradient between Kentucky, Indiana, and Ohio meant that shallow water facies in the south differed markedly from deeper water facies in the north. These lithological changes may even be present within state boundaries. For example, the gray shales of the Waynesville Formation of Ohio (upper Dillsboro Formation of Indiana) grade into the rubbly limestones of the Bull Fork Formation in northern Kentucky, which eventually become the greenish, peritidal dolosiltites of the Rowland Member of the Drakes Formation in central Kentucky.

In most cases, we defer to the standard terminology of Kentucky. However, we diverge on several occasions, primarily because we establish long-distance correlation and allostratigraphic (rather than lithostratigraphic) unit definitions. These differences are noted and explained, and the corresponding local lithostratigraphic names and ranks will be given for reference (Fig. 3).

Upper Ordovician

The Upper Ordovician of the Cincinnati Arch is among the most famous Paleozoic deposits in the world (Meyer and Davis, 2009). A well-preserved, diverse fauna coupled with extensive, well-exposed strata has inspired nearly two centuries of study. Ordovician strata exposed on the west side of the Cincinnati Arch are exclusively Cincinnatian (Katian, uppermost Ka1 to Ka4 stage slices) in age. The older Mohawkian Series (upper Turinian to Chatfieldian; Sandbian, Sa2 to Katian, Ka1) High Bridge Group and Lexington Limestone are primarily exposed around the Jessamine Dome to the east, outside the field-trip area.

Seminal work by Holland and Patzkowsky (1996) divided the Cincinnatian Series into six 3rd-order depositional sequences, C1 through C6. Our research has led us to reinterpret and revise these sequences into C1 through C8, with many of the sequences further subdivided into 4th-order subsequences, each assigned a letter suffix (e.g., C5A, C5B, etc.). The current revised version debuted in Brett et al. (2018a) and is summarized below, with emphasis on the interval featured on the field trip (Figs. 3, 4).

Sequences C1 and C2: Kope Formation and Fairview Formation

The oldest well-exposed beds on the west side of the Cincinnatian Arch are those of the lower Cincinnatian Series, commencing with the Kope Formation (sequence C1) and Fairview Formation (sequence C2). The Kope represents the entire Edenian Stage (lower Cincinnatian) and is typified by cyclic alternations of medium-gray, sparsely fossiliferous shales (~75%), siltstones, and thin shell hash limestones. Time-equivalent strata that record shallower depositional environments are mapped as the Clays Ferry Formation (in part) and Garrard Siltstone in central Kentucky. The Fairview Formation is considerably more limestone rich and marks the base of the middle Cincinnatian Maysvillian Stage (middle Katian, lower Ka2), overlying the Kope at the C1/C2 sequence boundary. This interval is locally mapped as the Calloway Creek Limestone in central parts of Kentucky. These units have been the subjects of numerous studies of sedimentology (Tobin, 1982; Jennette and Pryor, 1993), faunal gradients (Holland et al., 2001; Miller et al., 2001), microstratigraphy, sequence stratigraphy (Brett et al., 2003a, 2008b), chemostratigraphy (Bergström et al., 2010a), and magnetic susceptibility (Ellwood et al., 2007, 2012). Much of this research was summarized in detail by McLaughlin et al. (2008c) and papers therein, and Brett et al. (2012c), and the reader is referred to those volumes. These units will not be observed on the present field excursion and are not further considered herein.

Sequence C3 (Revised): Bellevue and Corryville Members of the Grant Lake Formation

The oldest unit reviewed in detail on this field trip is the Grant Lake Formation (Schumacher et al., 1991), a thick package of limestone and minor shale that forms the upper half of the Maysvillian Stage (middle Cincinnatian; middle Katian, upper Ka2). Although its type region is on the east side of the Cincinnati Arch, near Maysville, Kentucky, the western Grant Lake is quite similar in most regards, with a rubbly weathering, argillaceous, fossiliferous limestone being the predominant lithology. In northwestern Kentucky, the unit is best exposed along I-71 at the Carroll/Trimble County line and on various state highways near Shelbyville and Taylorsville. Southward, the facies record shallower depositional environments, and correlative strata are mapped as various members of the Ashlock Formation in central Kentucky (Weir et al., 1965, 1984). The lower Grant Lake Formation constitutes the C3 depositional sequence. Its basal subunit, the Bellevue Member, is a transgressive package of coarse crinoidal grainstones or brachiopod packstones, locally with herringbone cross-stratification. Along Kentucky Route 55 north of Shelbyville, the member contains a major deformed bed, one of the youngest in the local succession. The Bellevue thickens southward and becomes considerably more argillaceous, transitioning into the greenish, peritidal Tate Member of the Ashlock Formation. Near Bedford, Kentucky, the Bellevue Member is overlain by the oncolitic packstones and shaly, nodular limestones of the Corryville Member (middle Grant Lake Formation; the C3 HST), often including the large brachiopods Vinlandostrophia (formerly Platystrophia) ponderosa, Rafinesquina, and Hebertella, along with massive bryozoans (e.g., Monticulipora). The Bellevue-Corryville contact is interpreted as a major flooding surface and locally shows evidence for submarine corrosion indicative of sediment starvation (e.g., at Shelbyville, Kentucky).

Sequence C4 (Revised): Mount Auburn Member of the Grant Lake Formation and Arnheim Formation

The uppermost Grant Lake Formation (sensu stricto) comprises the Mount Auburn Member. In the Louisville area, the Mount Auburn is a 1.5- to 3-m-thick, coarse, phosphatic skeletal grainstone interpreted to be the TST of sequence C4 (Fig. 4) in contrast to Holland and Patzkowsky (1996), who included it within their sequence C3. Thus, although the Mount Auburn Member is technically defined as the uppermost unit of the Maysvillian Stage, we consider it genetically linked to the major transgressive systems tract of the lower Richmondian Stage (i.e., lowermost upper Cincinnatian; Katian, uppermost Ka2 to lower Ka3). However, we do not redefine the Maysvillian-Richmondian stage boundary, leaving it at the base of the Arnheim Formation.

The thick, shaly Arnheim Formation of Ohio overlies the Mount Auburn Member at a major flooding surface and is interpreted as the C4 HST (Fig. 4). This interval of interbedded greenish-gray shale and skeletal pack- and grainstone is commonly mapped as the lower part of the Bull Fork Formation in Kentucky (e.g., Kepferle, 1977). Alternately, near Louisville, it is mapped as the uppermost part of the Grant Lake Formation based on its lithology (Kepferle, 1976a, 1976b, 1976c, 1977). However, its identity, based on its position in the succession and brachiopod fauna, is still open to question. According to Butts (1915), the lower Arnheim Formation in the Louisville area comprises a 9–10 m interval, the “Platystrophia ponderosa zone” (now “Vinlandostrophia ponderosa zone”), and is a thickened, shale facies of the Sunset Member of the eastern side of the Cincinnati Arch; if so, this interval has undergone substantial thickening and facies change. At present, we interpret the “V. ponderosa zone” as the upper part of the Grant Lake Formation or Corryville Member (sequence C3B). An overlying 1.5-2.5-m-thick cross-bedded, orange weathering grainstone, seen prominently on the new outcrops on U.S. Highway 31E visited herein, is interpreted as the Mount Auburn Member. By this interpretation, the Mount Auburn is overlain by a very condensed (or absent?) Sunset Member interval and the undisputed Oregonia Member, ~3-7 m thick. This is more in line with relative thicknesses seen on the eastern side of the Cincinnati Arch (Brett et al., 2018a). However, further study is required to confirm these correlations, so they are only tentatively identified in our diagrams.

The Oregonia Member of the Arnheim Formation is readily identifiable as Butts’s (1915),“Rhynchotrema dentatum zone.” Not only are there relatively few Vinlandostrophia ponderosa in this interval (rather, V. cypha becomes dominant), but the presence of Leptaena richmondensis, Rhynchotrema dentatum, and/or rare Retrorsirostra carleyi clearly fingerprint this interval as the Oregonia Member. Thus, to avoid confusion of our allostratigraphic definition for the Grant Lake Formation and improve multistate correlation, we prefer to refer to this interval as the Arnheim Formation. The thick grainstone of the Mount Auburn Member forms a suitable marker bed for the base of sequence C4. The Arnheim is regionally notable as the lowermost unit of the provincial Richmondian Stage. Furthermore, the zonally significant conodont Amorphognathoides ordovicicus first appears in the uppermost Arnheim (Bergström et al., 2010a), marking the beginning of the A. ordovicicus Zone and the base of the Katian, Ka3 stage slice. See Foerste (1912) for an extensive review of the Arnheim interval, including regional comparisons.

Sequence C5 (Revised): Lower Rowland Formation

The C5 sequence of Holland and Patzkowsky (1996) included the entire middle Richmondian, consisting of the Waynesville, Liberty, and Whitewater formations. Extensive field study has shown the presence of previously unrecognized unconformities within this interval, leading us to split it into revised sequences C5, C6, and C7 (Brett et al., 2018a; Fig. 4).

The middle Richmondian (upper Katian, Ka3) Waynesville Formation is traditionally divided into three members: Fort Ancient, Clarksville, and Blanchester, all named for locations in southwest Ohio. The formation was recently reviewed and revised by Aucoin and Brett (2016) and we follow their sub-member nomenclature. The lower two members, and correlative strata, are herein assigned to the C5 sequence, which is broken down into 4th-order C5A, C5B, and C5C subsequences. Where typically developed in Ohio and Indiana, the Waynesville Formation commences with a compact, phosphatic, Cincinnetina-rich grainstone that unconformably overlies the Arnheim Formation. This bed or package of beds, dubbed the South Gate Hill submember of the Fort Ancient Member by Aucoin and Brett (2016), has been interpreted as a condensed transgressive package sitting on the C4/C5 sequence boundary (the C5A TST). It is overlain by mostly barren lower Fort Ancient shale, which, in turn, is overlain by the ledgy Bon Well Hill submember (the C5B TST), typically rich in the brachiopods Rafinesquina and Cincinnetina meeki. The upper Fort Ancient shale (the Harpers Branch submember of Aucoin and Brett, 2016; the C5B HST) is a more sparsely fossiliferous butter shale that was termed the Treptoceras duseri shale or “trilobite shale” by Frey (1987, based on the abundance of this nautiloid cephalopod or well-preserved Flexicalymene and Isotelus trilobites. The Fort Ancient Member, specifically the Bon Well Hill submember, shows peak values of δ13Ccarb in the globally recognized Waynesville positive δ13Ccarb excursion of Bergström et al. (2010a); see (Aucoin et al., 2018).

In Kentucky, the lower Waynesville (Fort Ancient) Formation is a distinctive chalky weathering, somewhat rhythmically bedded limestone variously mapped as the middle or upper part of the Bull Fork Formation or the lower part of the Rowland Member of the Drakes Formation. Our field observations indicate that the Rowland is nearly equivalent to the Waynesville Formation (contra Holland and Patzkowsky, 1996, who considered it equivalent to the upper Arnheim Formation and a part of their sequence C4). Herein we refer to the Rowland with the nonstandard rank of “formation” (lower case) based on its close correlation to the Waynesville Formation, distinctive lithology, and considerable thickness (typically on the order of 15–20 m).

The lower member of the Rowland formation locally comprises distinctive subunits. First, in the Louisville-Mount Washington area, a lower, 30–60-cm-thick highly phosphatic, brachiopod-rich pack- to grainstone is overlain by richly fossiliferous muddy packstones, typically with whitish silicified brachiopods, and was referred to by Butts (1915) as the “Constellaria polystomella zone”; its thickness appears to be locally variable from ~4-9 m. This interval is likely equivalent to the South Gate Hill submember at least in part and thus we consider it the base of the Rowland formation as defined herein (the C5A TST). Second is a mostly barren lower shaly package (the C5A HST), which in the Mount Washington area contains hummocky laminated calcisiltites with amoebiform chert nodules (in some quadrangles this has been mapped by the USGS [U.S. Geological Survey] as the base of the Rowland). Third, the Fisherville submember is a 1.5-2-m-thick package of very rhythmic decimeter-scale micritic lime mudstone or wackestone, alternating with dark, algae(?)-bearing shale, named after a town east of Louisville where this unit was well exposed. This interval is very distinctive and has also been used to demarcate the base of the Rowland formation in several quadrangle maps (e.g., Kepferle, 1976b, 1976c, 1977). The Fisherville submember locally contains Tetradium and Cyathophylloides (a colonial rugose coral, often called Columnaria or Favistella in older literature) in what is sometimes known as the Columnaria zone (Butts, 1915), or the “Fisherville reef” (Foerste, 1909; Browne, 1964). We argue that the Fisherville is equivalent to the Bon Well Hill submember (and thus the C5B TST) based on its carbon isotope patterns (Aucoin et al., 2018). Finally, fourth, the Fisherville is overlain by greenish-gray shales that are often full of the small domal trepostome bryozoan Cyphotrypa and thus called the “Cyphotrypa shale” by Butts (1915). To the north, these beds are overlain by yet more fossiliferous dolomitic mudstone that may represent the middle Waynesville Formation (the Clarksville Member of Indiana and Ohio; our C5C).

Sequence C6 (Revised): Upper Rowland Formation and Bardstown Formation

Southward from Mount Washington, the Cyphotrypa bed, Fisherville rhythmites, barren shales, South Gate Hill-equivalent beds, and upper Arnheim Formation appear to be successively truncated beneath the massive upper member of the Rowland formation at the “mid Richmondian” unconformity (Brett et al., 2015b; Aucoin and Brett, 2016; Fig. 4), the C5/C6 sequence boundary. Recognition of this heretofore-unrecognized angular erosional surface is a major driver for our subdivision of Holland and Patzkowsky’s (1996) C5 sequence (e.g., Brett et al., 2015b). This unconformity lies within the Waynesville Formation, roughly at the Clarksville/Blanchester member boundary in Ohio and Indiana, where it is rather cryptic. However, it becomes increasingly noticeable southward (up-ramp). Eventually, near Bardstown, Kentucky, the upper Rowland rests on the Leptaena-and Rhynchotrema-bearing beds of the Oregonia Member of the Arnheim Formation, locally termed the Reba Member of the Ashlock Formation (Brett et al., 2015b).

Our revised C6 sequence sits atop this unconformity and comprises the Blanchester Member of the Waynesville Formation (and its lateral equivalents in the upper Rowland formation) as well as the overlying Liberty Formation. The latter is equivalent to the Bardstown Member of the Drakes Formation. As with the Rowland, we informally promote the Bardstown to formational rank in this chapter to improve consistency across state lines, using “formation” in lower case to signify this informality.

In northern Kentucky, near Bedford, a set of gastropod-rich grainstones (the Marble Hill beds of Swadley, 1979) abruptly pass laterally into the upper Rowland, a 5–15 m-thick succession of cream-colored, moderately fossiliferous nodular to massive, burrowed, dolomitic argillaceous wackestone with sporadic dark shale partings. The interval has a moderate fauna of brachiopods, especially Hebertella, Rafinesquina, and Vinlandostrophia. Corals are somewhat common, with rugose (horn) corals (Grewingkia, Streptelasma), colonial rugosans (Cyathophylloides), and Tetradium at one or two horizons, especially in the upper layers.

Southward, near Mount Washington, these become massive, bioturbated to laminated, sparsely fossiliferous lime mudstones. A few levels of greenish shaly micrites contain abundant domal bryozoans (Cyphotrypa). Intervals of vertical burrows filled with a dark-green mineral (verdine) alternate with laminated beds. The exact meaning of these time-specific facies (sensu Brett et al., 2012b; Ferretti et al., 2012) remains incompletely understood, but they grade further southward (up-ramp) into wavy laminated, greenish shaly micrites with desiccation cracks that surely record lagoonal to inter- and supratidal environments, possibly an early transgressive systems tract in which sedimentation kept pace with slow base-level rise.

In contrast to the sparsely fossiliferous upper member of the Rowland formation (C6A), C6B—the Liberty Formation and correlative Bardstown formation—is significantly more limestone rich and highly fossiliferous. It also shows much less facies change up-ramp (southward): the gray, lenticular to tabular wackestones and packstones of the Liberty are not dissimilar to the brown-weathering rubbly packstones of the Bardstown formation, and both carry a diverse marine fauna. In its type region near Bardstown, Kentucky, the lower 2 m of the Bardstown formation feature two closely spaced coral biostromes, the “Bardstown reef(s)” (Butts, 1915; Browne, 1964), correlative to the Otter Creek coral bed of Simmons and Oliver (1967), which, in part, forms the C6B TST. These are packed with large hemispherical heads of colonial rugosans (Cyathophylloides), Calapoecia, favositids, and Tetradium. Locally, the lower bed also contains an abundance of large conical aulacerid stromatoporoids (Aulacera, formerly Beatricea). Upward, the Bardstown formation transitions into interbedded fossiliferous shales and packstones (the C6B HST) with a rich typical Richmondian fauna, especially the brachiopods Strophomena, Hiscobeccus, Hebertella, and Plaesiomys and the solitary rugose coral Grewingkia. Finally, the uppermost Bardstown formation comprises blocky, sparsely fossiliferous silty dolomudstones with abundant burrows and modiolopsid bivalves, interpreted as the C6 FSST. This interval may be correlated with the upper Liberty Formation to the north, which often features silty, argillaceous limestone with a comparatively meager fauna characterized by trace fossils.

Sequence C7 (New): Lower Whitewater Formation

The Whitewater Formation of Ohio and Indiana (upper Richmondian; Katian, Ka3-Ka4) is a fossiliferous limestone-dominated unit that overlies the Liberty Formation. It is often broken into two semi-formal members, the lower Whitewater and upper Whitewater, locally with a major dolostone package, the Saluda Member, in between (Hatfield, 1968). Originally part of Holland and Patzkowsky’s (1996) C5 and C6 sequences, we consider most of the Whitewater Formation to represent its own sequence, C7 in our revised Cincinnatian classification (Fig. 4). Note that we prefer the term “Whitewater” (Nickles, 1903), as used in Indiana and Ohio, instead of the “Drakes” Formation (Weir et al., 1965), as formally mapped in Kentucky, based on precedence and because its facies and subunits are very similar across the state lines within the field-trip area.

Along the west side of the Cincinnati Arch, the lower Whitewater Formation is sharply set off from the underlying dolomitic mudstones by a surface interpreted as the C6/C7 sequence boundary. At the base, a distinctive package of limestone to dolostone, full of orange-weathering, and recrystallized bryozoans is interpreted as a transgressive succession and informally named the Buckner submember for exposures at Buckner, Kentucky (Stop 2-2A). This is overlain by two or more closely spaced colonial coral biostromes previously known as the “Madison reef (Browne, 1964) for typical occurrences near Madison, Indiana, where they contain massive (sometimes over 1 m in diameter) heads of the coral Cyathophylloides stellata (formerly Columnaria or Favistella alveolata). Tetradium is also present in certain layers, particularly near the top, and the sponge Dystactospongia madisonensis is found locally. These fossiliferous beds were historically included in the Saluda Member of the Whitewater Formation (Hatfield, 1968). We informally refer to them as the “lower Saluda submember,” for lack of a better name, whereas the massive “upper Saluda submember” (or “true Saluda”) forms the bulk of the unfossiliferous, or sparsely fossiliferous dolostone typical of the member. In turn, these biostromes are overlain by a thin, widespread succession of alternating dark shales and dolostones (sometimes containing black strap-like remains, possibly algae) interpreted as the highstand deposits of C7A, which may be truncated in the south by an erosion surface beneath the overlying upper Saluda submember (i.e., the C7A/C7B sequence boundary).

Near Louisville, the upper Saluda consists of massive, rhythmically laminated, desiccation cracked pale orange-buffweathering, silty dolostones up to ~12 m thick. We interpret the massive dolostones of the Saluda Formation to represent the early transgressive systems tract of the C7B cycle. This laminated dolostone facies does not extend to the east side of the Cincinnati Arch, but time-equivalent strata are likely represented in the greenish dolomitic shales of the Preachersville Member of the Drakes Formation (in part). Neither does the facies persist to the north, where it thins markedly down-ramp, apparently passing laterally into a bundle of limestones in the middle of the Whitewater Formation.

The highstand of the C7B sequence consists of the rubbly packstones of the upper Whitewater Formation. The typical expression of these beds is exposed near Richmond, Indiana, and adjacent Ohio, where they are famously fossiliferous. The typical upper Whitewater fauna includes bryozoans, brachiopods (especially Vinlandostrophia acutilirata, Rhynchotrema dentatum, Holtedahlina sulcata, and Hebertella), bivalves, cephalopods, and gastropods, some coral- or bryozoan-encrusted. Southward, this unit thins and becomes more dolomitic, possibly transitioning into the Hitz beds (or Hitz Member of the Whitewater Formation), a poorly known unit best exposed near Madison, Indiana, and into adjacent northern Kentucky. However, this correlation is not certain and the Hitz could also be slightly younger.

Sequence C8 (New): Uppermost Whitewater Formation and Elkhorn Formation

The uppermost Cincinnatian depositional sequence, only fully developed near Richmond, Indiana, was originally designated C6 by Holland and Patzkowsky (1996). Following the renumbering of underlying sequences, we revise it to C8 (Fig. 4). This latest Katian (Ka4) sequence consists of at least two smaller-scale carbonate-shale cycles. The lower C8A has a thick basal transgressive carbonate portion (presently mapped as the uppermost Whitewater Formation) with abundant bryozoans and brachiopods, especially Rhynchotrema dentatum, which is followed by an interval of nearly barren, relatively pure blue-gray clay (the basal Elkhorn Formation shale). Locally, a sharp contact with a compact grainstone bed and marly wacke- to packstone, sometimes with Tetradium and stromatoporoids, marks the base of a poorly known highest Cincinnatian sequence (C8B). The latter unit grades upward into greenish-gray, sparsely fossiliferous shale. In southwestern Ohio and northern Kentucky, this upper shale contains a thin tongue of maroon sediment, the feather edge of the Queenston delta complex creeping in from the east. These beds have long been known as the Elkhorn Formation but are currently mapped as part of the Preachersville Member of Drakes Formation in Ohio and Kentucky. Siltstones assigned to the Hirnantian(?) Centerville Formation overlie the Preachersville Member on the eastern flank of the Cincinnati Arch. However, both units are eroded out at the Cherokee unconformity on the western flank, except for local patches of dolomitic pack- and rudstone, bearing stromatoporoids and a distinctive molluscan fauna that rest sharply on the Saluda Formation. This unit, the Hitz Member of the Whitewater Formation, requires further study, but may represent either upper C7 or C8 strata.

Silurian

The Silurian geology of southeastern Indiana and adjacent west-central Kentucky has a long history of study, beginning with the pioneering efforts of Owen (1838, 1839, 1857). Stratigraphic and paleontological studies that examined the entire Silurian succession in this region were completed by Foerste (1897, 1898, 1904, 1906, 1931, 1935), Busch (1939), and Kovach (1974). French (1968) studied the lithostratigraphy and petrography of the Silurian (and Devonian) rocks of southeastern Indiana, and Peterson (1981) and Ettensohn et al. (2013) extended those studies into west-central Kentucky. Surprisingly, the Silurian strata of this area have received more detailed study than those of west-central Ohio, though several studies have stretched from southeastern Indiana into that region (e.g., Busch, 1939; Kovach, 1974; Ettensohn et al., 2013), exploiting the great similarity in the strata on either side of the state line. The Silurian strata of the Appalachian Basin and surrounding areas have been assigned to a continuous series of 3rd-order sequences, each assigned a Roman numeral (see also Brett and Ray, 2005; McLaughlin et al., 2008b; Cramer, 2009; Cramer et al., 2006a, 2006b; Sullivan et al., 2014, 2016; Waid, 2018b) (Fig. 5). New work in northern Indiana (McLaughlin et al., 2018) has slightly modified the sequences of the upper Silurian (especially sequences VII through X) and those modifications have been adopted in this paper as well (Figs. 3, 5, 6).

Figure 5.

Schematic stratigraphic column of the Silurian formations in the region of Louisville, Kentucky, and correlative units in southwestern Ohio. Not scaled to absolute time. Adapted from McLaughlin et al. (2008b).

Figure 5.

Schematic stratigraphic column of the Silurian formations in the region of Louisville, Kentucky, and correlative units in southwestern Ohio. Not scaled to absolute time. Adapted from McLaughlin et al. (2008b).

Figure 6.

Idealized stratigraphic column, chronostratigraphy, and sequence stratigraphy of the Silurian and Devonian succession in the region of Louisville, Kentucky. Abbreviations: A. ramosa—Amphipora ramosa; Fm—formation; Ls—limestone; Mbr—Member; Sh—shale. Absolute dates from Melchin et al. (2012) and Becker et al. (2012),in Gradstein et al. (2012). Adapted from figure 3 of Goldstein et al. (2009).

Figure 6.

Idealized stratigraphic column, chronostratigraphy, and sequence stratigraphy of the Silurian and Devonian succession in the region of Louisville, Kentucky. Abbreviations: A. ramosa—Amphipora ramosa; Fm—formation; Ls—limestone; Mbr—Member; Sh—shale. Absolute dates from Melchin et al. (2012) and Becker et al. (2012),in Gradstein et al. (2012). Adapted from figure 3 of Goldstein et al. (2009).

Cherokee Unconformity

The Cherokee unconformity marks the Ordovician-Silurian boundary, separating the Creek (lower Tippecanoe) and Tutelo (upper Tippecanoe) megasequences. With a gap that stretches from the late Katian to the Rhuddanian or even Aeronian, this horizon represents roughly 3–5 million years of missing time, the result of erosion and nondeposition due to the global sea-level drawdown during the latest Ordovician (Hirnantian). Particularly good examples of the irregular, karst unconformity are present in the vicinity of Crestwood, Kentucky (Stop 2-3), which feature irregular, backfilled, and steep-sided to undercut pockets. These are interpreted as epikarst fills on the unconformity surface (Brett et al., 2014).

Sequence S-I: “White” Brassfield Formation

Sequence S-I (Silurian I) is represented on the Cincinnati Arch by the mid- to upper-Rhuddanian informal “white” member/lithofacies of the Brassfield Formation in western/southwestern Ohio and eastern Indiana, and correlates to the type Brassfield of central Kentucky (Foerste, 1906; Brett and Ray, 2005; McLaughlin et al., 2008b; Sullivan and Brett, 2013; Sullivan et al., 2016). So-named for its pale, locally cherty crinoidal limestones, the “white” Brassfield is best exposed near Dayton, Ohio, and is progressively truncated to the south and west (Foerste, 1904) by another informal member/lithofacies, termed the “golden” Brassfield. Although possibly present near Bardstown, Kentucky, S-I is absent in the Louisville area.

Sequence S-II: “Golden” Brassfield Formation

The Brassfield Formation of the western Cincinnati Arch is primarily represented by the golden member/lithofacies, a relatively thin (often only about a meter thick) unit of pinkish-to-yellowish coarse grainstone. Bedding is often cryptic or highly irregular. The unit typically lies atop Upper Ordovician strata (usually Whitewater Formation) at the Cherokee unconformity, locally with up to 2 m of relief (Brett et al., 2014). Fossils are typically highly fragmented, but identifiable corals, brachiopods, gastropods, and echinoderm debris may be found sporadically.

Based on carbon isotope data, the golden Brassfield likely correlates to the “red” Brassfield of western/southwestern Ohio, which in turn correlates with the middle-to-late Aeronian Oldham Member of the Drowning Creek Formation (sensu Sullivan et al., 2016) of central Kentucky and southern Ohio. This is consistent with conodont evidence (Rexroad et al., 1965; Rexroad, 1967, 1980; Nicoll and Rexroad, 1968; Brett et al., 2014). Brett and Ray (2005) consider the Oldham Member to represent the transgressive phase of the second 4th-order cycle within the 3rd-order S-II of the Appalachian Basin. Thus, S-II is only partially preserved west of the Cincinnati Arch.

An additional Brassfield lithofacies, the “cherty” Brass-field, is also present on the west side of the Cincinnati Arch, near Bardstown, Kentucky, and southward into Tennessee. This manifestation of the Brassfield Formation is often considerably thicker than the golden Brassfield (e.g., Rexroad, 1967, reported a ~6.7 m measurement at Bardstown) and may contain discernible subunits, including a lower massive, fine-grained dark-gray bed ~1.5 m thick (Rexroad, 1967; K. Hartshorn, 2017, personal observation). Research into the precise age and correlation of this southwestern Brassfield is ongoing; it may represent parts of both S-I and S-II. Further information regarding regional facies variation in the Brassfield Formation can be found in Gordon and Ettensohn (1984) and Norrish (1991).

Sequence S-III: Lee Creek Formation

A relatively thin unit (usually less than 1 m thick) composed of heavily bioturbated green, red, or tan weathering dolosiltite, the Lee Creek Formation was originally identified by Foerste (1897) and later described as the Lee Creek Member of the Brassfield Formation by Nicoll and Rexroad (1968). However, the occurrence of conodonts diagnostic of the Pterospathodus eopennatus Superzone indicate a Telychian age (Te2 or younger) for this unit, notably younger than the underlying golden Brassfield and likely separated by a significant unconformity (several conodont zones). Therefore, Brett et al. (2012a) removed the Lee Creek from the Brassfield and elevated it to formational rank, as it is distinguishable both lithostratigraphically and biostratigraphically (Figs. 5, 6).

The Telychian age and lithological similarities of the Lee Creek Formation to the two-part, orange-weathering dolostones of the Waco Member of the Alger Formation in central Kentucky and southern Ohio (Sullivan et al., 2014) suggest that the units are chronostratigraphically equivalent, and were likely coextensive across the Cincinnati Arch. The Waco is made up of three informal subunits in southern Ohio—the “white,” “orange,” and “upper shaly” Waco—that represent two small-scale transgressive/regressive cycles superimposed on the TST of S-III. Since all of the subunits of the Waco are within the Pterospathodus eopennatus Superzone, it is unclear which bed(s) the Lee Creek Formation correlates to. Subsurface correlations of the Waco by Waid (2018b) in southern Ohio suggest that the white Waco may be truncated under the orange Waco by a slight, regionally angular unconformity. If the orange Waco truncates underlying strata up the Cincinnati Arch, it is more likely that the Lee Creek, deposited high on the arch, correlates to the orange Waco strata. Additionally, the presence of a slight angular unconformity within the Waco Formation provides additional evidence that far-field tectonic influence from an early phase of the Salinic orogeny (see Ettensohn et al., 2013) combined with eustasy to influence the depositional patterns of S-III throughout the Appalachian Basin and surrounding regions.

Sequence S-IV: Osgood Formation

The Osgood Formation (restricted usage, formerly the lower member of the Osgood Shale; see Brett et al., 2012a, for discussion and revisions) is a conspicuous lithological unit in the Louisville, Kentucky, area and surrounding region, where it is composed of up to ~10 m of rhythmically alternating decimeter-scale dolostones and dolomitic shales (Figs. 5, 6). These beds show a distinctive stacking pattern and have been studied in detail by Thomka (2015); careful measurements suggest that individual beds may be widely traceable, providing strong evidence for a primary origin, as opposed to a diagenetic origin as suggested for some similar rhythmites (Munnecke and Samtleben, 1996). Many of the limestones show ichnofossils, including Chondrites and Planolites, but are otherwise sparsely fossiliferous, owing, in part, to dolomitization. The upper parts of the formation occasionally contain pelmatozoan ossicles and in the type area near Osgood and Napoleon, Indiana, the unit is less strongly dolomitic and carries a moderately diverse fauna of brachiopods (Atrypa, Eospirifer, Leptaena, Coolinia), small bryozoans, and echinoderms, of which the minute disparid crinoid Pisocrinus is particularly typical (Tillman, 1961; Frest et al., 1999). Conodonts from the Osgood Formation belong to the Pterospathodus amorphognathoides Zonal Group, spanning the latest Llandovery (late Telychian) to earliest Wenlock (Sheinwoodian).

In Indiana, the Osgood (sensu lato) and Laurel formations are considered members of the Salamonie Dolostone (Pinsak and Shaver, 1964). However, in Kentucky the same interval is referred to as the Osgood Formation and that practice is followed herein. The Osgood Formation grades to the southeast into the thick greenish-gray to maroon shales of the Estill Member of the Alger Formation (or Estill Shale) of central Kentucky and southern Ohio. The Estill is typically set off from the underlying “upper shaly” Waco strata by a few centimeters of dark-green pelletal glauconite. This horizon is the distal facies of the similarly glauconitic Dayton Formation of western Ohio, interpreted as the highly condensed TST of S-IV (Sullivan et al., 2016). A glauconite-bearing dolostone at the top of the Lee Creek Formation at Thixton, Kentucky (Stop 1-8), may be equivalent to this interval.

South of Louisville, the lower few meters of the Osgood Formation become a zone of alternating maroon and olive-gray shale, like the Estill Shale to the east. This color banding persists southward to Bardstown, Kentucky, and even ranges into northern Tennessee (e.g., along U.S. Highway 31E south of Westmoreland). Similar coloration is present to some extent west of Nashville, near Pegram, Tennessee (Thomka, 2015), though the facies is more carbonate rich and mapped as a part of the Wayne Group (Barrick, 1983). Indeed, reddish and green offshore marine facies are widespread during the Llandovery, especially in the upper Telychian (Ziegler and McKerrow, 1975), and form an outstanding example of a time-specific facies that has been associated with “oceanic oxic events” (Brett et al., 2012b; McLaughlin et al., 2012).

The Osgood/Estill interval records the largest sea-level highstand of the Silurian (the S-IV HST), associated with the onset of the major Ireviken bioevent. This event is concurrent with a major disturbance in the global carbon cycle, reflected in the rock record by a major positive δ13C excursion often termed the “Ireviken Excursion” (Cramer and Saltzman, 2005, 2007; Cramer and Munnecke, 2008). The Osgood Formation contains the ascending limb of this excursion, with steadily rising values through much of the unit. An initial peak is present within the uppermost 1–2 m, roughly coincident with a ledge-forming carbonate package designated the “Crestwood beds” for exposures near Crestwood, Kentucky (Thomka, 2015; see Stop 2-3).

Sequence S-V: Lewisburg Formation and Massie Formation

The Osgood Formation is overlain by a thin package of compact dolostone and dolomitic limestone, formerly termed the “middle Osgood limestone” (Foerste, 1897), “upper Osgood carbonate,” or even the “Laurel Dolomite” in Ohio (see discussion in McLaughlin et al., 2008b, and Brett et al., 2012a; Figs. 5, 6). To improve regional correlation and clarify terminological ambiguities, McLaughlin et al. (2008b) and Brett et al. (2012a) assigned this carbonate to the Lewisburg Formation, reintroducing a name used by Kovach (1974). Based on its lithology, the unit may also be styled the Lewisburg Dolostone.

The Lewisburg sharply overlies the Osgood Formation at a contact we interpret as the S-IV/S-V sequence boundary. Though the original fabric is largely altered by diagenesis, weathered surfaces suggest that the unit was a pelmatozoan packstone to grainstone. Brachiopods, especially Atrypa, Meristina, and Whit-fieldella, are locally common. Near the top, small bioherms, apparently composed of algal/microbial boundstone and fistuliporoid bryozoans, may extend upward from slightly below the Lewisburg contact into the overlying shale for up to 0.5 m, demonstrating the conformable nature of this contact (Thomka and Brett, 2015a, 2015b).

These superjacent dolomitic gray shales and mudstones are assigned to the Massie Formation, commonly called the Massie Shale, and formerly known as the “upper Osgood shale” until recent promotion to formational rank (McLaughlin et al., 2008b; Brett et al., 2012a). The Massie is rather thin, typically less than 2 m in Ohio, Indiana, and northern Kentucky; southward, it is truncated to less than 20 cm at Bardstown, Kentucky. Although frequently unfossiliferous, the Massie Formation is noted for an extremely rich macrofauna at a few localities that have escaped dolomitization, particularly in Ripley County, Indiana. A handful of highly productive quarries and natural exposures have yielded more than 160 taxa, including small corals, bryozoans, brachiopods, mollusks, trilobites, and echinoderms (Frest et al., 1999, their tables 45.41 and 45.43; Thomka and Brett, 2015a, 2015b; Thomka et al., 2016).

The Massie Formation is best known for the latter, which include unusual disparid crinoids (Paracolocrinus paradoxicus, Calceocrinus spp., Eohalysiocrinus cf. stigmatus, etc.), coronoids (Stephanocrinus and Cupulocorona), the hemicosmitid Caryocrinites, the youngest known eocrinoid (Ampheristocystis;Frest, 2005), and a diverse assemblage of diploporitan “cystoids” collectively known as the Holocystites Fauna (Frest et al., 2011). These squatty, globular echinoderms have been extensively studied in recent years, with research focusing on their taphonomy (Thomka et al., 2016) and paleoecology (Frest et al., 2011; Thomka and Brett, 2015a, 2015b), as well as their taxonomy and phylogeny (Sheffield, 2017; Sheffield and Sumrall, 2017). The Holocystites Fauna appears to have been endemic to the Indiana region, as it is rarely found elsewhere. In contrast, the associated coronoids and hemicosmitids are more widespread; these groups likely originated around other paleocontinents and only arrived in the seas of Laurentia during the Silurian (Frest et al., 1999, 2011).

This macrofauna has long been used to correlate the Lewisburg Formation and Massie Formation with the Irondequoit Limestone and Rochester Shale (respectively) of New York. Bassler (1906) reported that the Massie bryozoan fauna, with over 50 species, almost completely overlaps with that of the Rochester. Similarly, the occurrence of coronoids and Caryocrinites forms another link between the two regions. However, conodont biostratigraphic data seemingly do not support this correlation, rendering it controversial. Conodonts from the upper Lewisburg and Massie in Ohio include Kockelella walliseri, the nominal species of the lower K. walliseri Zone. In contrast, the Rochester Shale contains a fauna indicative of the upper K. ranuliformis Zone to Ozarkodina sagitta rhenana Zone. Both the upper K. ranuliformis and O. s. rhenana Zones are, based on current understanding, stratigraphically lower than the K. walliseri Zone (Cramer et al., 2010a, 2010b). Thus, conodont evidence would appear to correlate the Lewisburg and Massie not with the faunally similar Irondequoit-Rochester (S-V) succession of the Appalachian Basin, but rather with the upper Goat Island Formation of the Lockport Group (S-VI). This hypothesis further requires major removal of strata within or at the base of the Lewisburg Formation, for which there is little or no field evidence. These contrasting data indicate that either the nearly identical macrofauna of the Rochester and Massie formations is due to facies similarities of little correlation significance, or that the first appearance of K. walliseri is lower than previously thought. Given evidence for the diachronous first occurrence of this taxon between Baltica and Laurentia (Cramer et al., 2010b), the latter case seems most parsimonious.

Carbon isotope studies do not provide conclusive evidence on one side or other in the debate. Steadily rising δ13Ccarb values in the Osgood Formation indicate that these beds preserve the rising limb of the Ireviken (early Sheinwoodian) Excursion. A sharp drop in the overlying upper Lewisburg and basal Massie is variably interpreted. Cramer (in McLaughlin et al., 2008b) interprets this as indicating a strong truncation of section with a near absence of sequence S-V of the Appalachian Basin at a major unconformity within the Lewisburg Formation. Conversely, McLaughlin and Brett (in McLaughlin et al., 2008b) find no evidence for a major unconformity at this level, argue that fauna are fundamentally similar from the basal Lewisburg into the Massie, and interpret this negative shift in δ13Ccarb values as the preservation of an unnamed negative excursion in the lower Sheinwoodian of Gotland, New York, and elsewhere. High-resolution δ13Ccarb data (P. McLaughlin, 2018, personal observation) indicate strong similarities in the detailed δ13Ccarb patterns between sections separated by tens of kilometers. This consistency suggests that stratigraphic correlations of sequences across the Cincinnati Arch may be valid despite discrepancies in the first occurrence data of conodont taxa. Further data may help resolve these conflicting interpretations.

Sequence S-VI: Laurel Formation

A sharp erosional contact separates the shaly carbonates of the upper Massie from the overlying 10–13-m-thick, massive Laurel Formation or Laurel Dolostone (Figs. 5, 6), mapped farther north in Indiana as the Laurel Member of the Salamonie Formation. Locally, the basal Laurel is a package of tabular bedded dolomudstone or dolowackestone. This is overlain by a massive vuggy dolostone, originally fine-grained, grainstone, and wackestones with layered chert nodules that locally pass into limestone. Fossils are generally scarce, probably owing to diagenetic destruction, but near St. Paul, Indiana, where the Laurel is only slightly dolomitized, this interval yields a highly diverse and unique echinoderm fauna with more than 60 species of crinoids, including many unique genera (Frest et al., 1999). Brachiopods, bryozoans, and corals are surprisingly infrequent. This lower vuggy Laurel Dolostone is similar to and likely coeval with the Euphemia Dolostone of Ohio (McLaughlin et al., 2008b); we herein refer to it as the Euphemia Member.

The upper Laurel subunit is a conspicuously tabular, medium-bedded, pale buff dolostone with a fine-grained sucrosic texture and occasional white chert bands. This interval is sparsely fossiliferous but locally yields fully articulated calymenid trilobites. The distinctive lithological and taphonomic characteristics of this unit closely resemble those of the Springfield Dolostone of Ohio and we tentatively term it the Springfield Member. These facies represent a deeper shelf, low-energy setting with intermittent resuspension of sediments. However, an abundance of pentamerid brachiopods in the Springfield of Ohio suggests a BA-3 position for these tabular beds as with the underlying, more bioturbated Euphemia. Both units may show chert-filled Thalassinoides galleries. An uppermost unit of the Laurel Formation, equivalent to the Cedarville Formation of Ohio, is present in eastern Indiana but not readily identifiable in the Louisville, Kentucky, area, where it may be lithologically indistinguishable from the tabular Springfield Member, thinned, or missing.

The precise age of the Laurel Formation remains somewhat obscure owing to a sparsity of diagnostic conodonts. Its δ13Ccarb values are rather flat to slightly descending (~1.0-0.5‰), like those of the Euphemia and Springfield formations of Ohio. This nondescript profile suggests correlation with the upper Lockport Group (S-VI) in New York. However, this interpretation is in part contingent on the correlation of the Lewisburg-Massie interval to the Irondequoit-Rochester, and is thus controversial.

Sequence S-VIIA: “Limberlost” Oolite, Waldron Shale, and “Lower Louisville” Formation

The top of the Laurel Formation is locally developed into a thin (0-30 cm), oolitic dolostone. This unit is thought to rest unconformably on the underlying Laurel Dolostone as a thin tongue of the Limberlost Member of the Pleasant Mills Formation in Adams County, Indiana (Droste and Shaver, 1976; Figs. 5, Fig. 6). Large favositid corals occur at this level, which forms a bench in the Sellersburg Quarry. Small trilobite and crinoid fragments are found locally. The contact with the overlying Waldron Shale is abrupt and is developed as an encrusted hardground at the Waldron type section (Halleck, 1973), although it is obscured by being “welded” to the overlying dolomudstone at Sellersburg. This contact is interpreted as a maximum starvation surface.

The Waldron Shale comprises medium dark-gray to greenish-gray calcareous mudstone, shale, and argillaceous limestone ranging from 1.2 to 4 m thick. The formation has been famed as a source of exceptionally preserved Silurian fossils since its initial documentation by Hall (1879, 1882) and most detailed studies pertain to its macrofauna (e.g., Halleck, 1973; Rigby et al., 1979; Frest and Strimple, 1982; Peters and Bork, 1998, 1999; Watkins and McGee, 1998). However, the Waldron ranges from essentially barren to highly fossiliferous and can vary between these extremes over relatively short distances (Feldman, 1989). The fauna, where present, is highly diverse and includes more than 25 species of brachiopods, small rugose and favositid corals, fistuliporoid, fenestrate, and ramose trepostome bryozoans, gastropods, small bivalves, and trilobites (notably dalmanitids, Calymene, and Trimerus). The unit is also known for excellently preserved cystoids (Caryocrinites) and crinoids, especially Eucalyptocrinites, Lyriocrinus, and Periechocrinus, among other echinoderms. Bioherms are developed near the bottom and top of the Waldron Shale (Archer and Feldman, 1986; Schmidt, 2006). Small, micritic fistuliporoid bryozoan bioherms occur locally up to about a meter above the base. A second set of bioherms occurs in the upper meter of the Waldron, typically resting upon grainstone lenses a few tens of centimeters thick and a few meters wide that may represent small channel fills.

Certain beds contain exceptionally well-preserved fossils including fully articulated trilobites and complete crinoid crowns; these have provided important insights into tiering and paleoecology (Peters and Bork, 1998, 1999; Watkins and McGee, 1998). Furthermore, the taphonomy of these fossils indicates that Waldron muds accumulated in episodic pulses, either due to resuspension of local muds during storms or offshore-directed mud plumes derived from strong flooding of coastal source areas. The greenish-gray mudstones themselves are commonly very rich in euhedral pyrite, which occurs as minor burrow-fill replacements, small nodules, and crusts on many fossils. The large cubic crystals, as opposed to framboidal, fine-grained pyrite, point to a later diagenetic origin. Evidently, sulfate reduction commenced at substantial depth within the sediments (fossils are rarely, if ever, in-filled with pyrite framboids), and was followed by prolonged growth of pyrite crystals, which seem to have commonly nucleated on calcitic skeletons (Beier and Feldman, 1991). Another intriguing feature of Waldron taphonomy is the tendency of enclosed, articulated brachiopods, and crinoids to occur as uncrushed, calcite-spar-filled skeletons. The robust preservation of these fossils points to very early diagenesis of calcite fillings within the enclosures of rapidly buried skeletal remains. In this case, the calcite diagenesis appears to have predated pyritization and likely occurred in the upper zones of the sediment.

The surface and subsurface correlation of the Waldron Shale has received considerable attention (e.g., Price, 1900; Kindle and Barnett, 1909; Esarey et al., 1947; Esarey and Bieberman, 1948; Browne et al., 1958; Peterson, 1981; Conkin et al., 1992a, 1992b) and the unit has been considered a key for understanding the broader sequence stratigraphic patterns of the Silurian in the Great Lakes region (Shaver, 1996). Microfossil studies have included chitinozoans (Chaiffetz, 1972; Boneham and Masters, 1973), arenaceous foraminifera (McClellan, 1966), and ostracodes (Coryell and Williamson, 1936). Historical conodont sampling has revealed few diagnostic species (Rexroad et al., 1978). However, the age of the unit is constrained to the upper Wenlock (Homerian Stage).

More recently, δ13Ccarb studies of the Waldron near Newsom, Tennessee, revealed the presence of a dual-peaked positive δ13Ccarb excursion (Cramer et al., 2006a; Cramer, 2009). Subsequently a nearly identical, two-peaked excursion has been documented in the Waldron of southern Indiana (Danielsen, 2017). The distinctive nature of the δ13Ccarb excursion recorded in the Waldron, coupled with the relatively sparse conodont data from correlative strata in Tennessee (Barrick, 1983), indicates that this is the Mulde Excursion. The Waldron Shale is regarded as a widespread highstand deposit of the Homerian depositional sequence (i.e., the S-VIIA HST).

Sequences S-VIIB, C: Louisville and Wabash Formations

The Louisville Formation (typically called the Louisville Limestone), comprising 12–26 m of pale gray, medium- to thick-bedded, fine-grained dolomitic limestone, is well exposed in numerous new and older quarries around the Louisville, Kentucky, area and was used extensively in the past for building and paving stones. The Louisville’s total thickness varies substantially, as it is often truncated beneath the Jeffersonville Limestone by the major Wallbridge unconformity and locally by the younger sub-Beechwood unconformity. Its basal contact has been variably placed, but Conkin et al. (1992a) recognized an unconformity ~60 cm above the traditional (lithological) base and reassigned the intervening strata to the upper Waldron. The unconformity, which locally has slight channeling, is tentatively correlated with the sub-Guelph unconformity (the S-VIIA/S-VIIB sequence boundary) of the Appalachian Basin (Brett et al., 1990; McLaughlin et al., this volume).

The Louisville Limestone and adjacent units have been documented in considerable detail based on exposures at the Atkins Quarry near Jeffersonville, Indiana (Conkin, 2002). The basal 3–4 m of the Louisville, assigned to the informal Big Rock member by Conkin (2002), is an argillaceous, crinoidal, and locally cherty dolostone that is divided into about three packages (cycles) by thin but prominent shale seams. Bioherms are locally present in the lower 2–3 m (Anderson, 1980). An interval of ~2 m of massive skeletal packstone, rich in pentamerid brachiopods (Conchidium?), is present ~3 m above the base of the Louisville Limestone. Small silicified pentamerids and rugose corals may dissolve out freely from this zone in strongly weathered outcrops. Although this interval is assigned to the middle Big Rock member by Conkin (2002), the sharp basal contact of the pentamerid limestone may represent a minor sequence boundary, and the shell hash concentrates a TST. The overlying beds of this member consist of a series of rather even, medium-bedded, medium-to dark-tan limestone beds, which were given informal names by quarrymen (e.g., the “Granddad,” “Great Granddad,” and “Three Foot” ledges, each ~30-40 cm thick). The lower of these beds is fossiliferous and contains small corals. The uppermost 3 m of the Big Rock member is somewhat thicker bedded, and is a glauconitic and pyritic, somewhat fossiliferous wacke- to packstone containing abundant Arachnophyllum (colonial rugosans). These beds may reflect highstand carbonate deposition.

Higher beds in the Louisville Limestone, assigned by Conkin (2002) to the Shanks Quarry member, are flaggy (base) to very thick, bioturbated olive-gray to bluish-gray, sparsely fossiliferous dolostone (also with informal bed names that reflect their former use as curbing and paving stones because of a tendency to break into distinctive blocks: “Paving ledge,” “Blue Captain,” and “22 Inch ledge”). These facies are difficult to interpret because of the nearly complete absence of body fossils and sedimentary structures. They may reflect shallow burrowed lagoonal muds associated with regression.

The stratigraphy, sedimentology, and macrofaunal composition of the Louisville Limestone has been studied in southern Indiana and west-central Kentucky by Butts (1915), Browne et al. (1958), Conkin et al. (1992a, 1992b), and Conkin (2002), among others. These authors published many stratigraphic columns of the Louisville Limestone and other regional strata (one of which forms the basis for Fig. 3). Phelps (1990) recognized seven distinct lithofacies within the Louisville that suggested that this unit represents depositional environments ranging from peritidal to subtidal (above storm wavebase). Anderson (1980) studied the reefs of the Louisville Limestone in Bullitt County, Kentucky. Butts (1915) recorded a high diversity of corals (113 species). With synonymy, the richness can probably be trimmed to 70 species, still one of the most diverse partially silicified Silurian coral faunas in North America, including many tabulates (e.g., Favosites niagarensis, halysitids, and heliolitids) and both colonial (e.g., Arachnophyllum) and solitary rugosans. The Louisville also carries unusually well-preserved small stromatoporoids (Stock et al., 1997), which surprisingly escaped notice by Butts (1915); these are under study by C. Stock (2018, personal commun.). Other fauna includes diverse mollusks, rare trilobites, crinoids, and plates of the hemicosmitid rhombiferan “cystoid” Caryocrinites.

The formation also yields diverse brachiopods (61 species according to Butts, 1915), some of which are of biostratigraphic importance. For example, Droste and Shaver (1976) reported Pentamerus sp. in the lower (Big Rock) member, suggesting an upper Wenlock (Homerian) position. Meanwhile, the occurrence of the pentamerids Kirkidium and Ectorhipidium trilobatum in the upper few meters, as well as other macrofauna in the Louisville, indicates an early Ludlow (Gorstian) age for these beds.

The overlying Wabash Formation, locally removed by erosion at the Wallbridge unconformity in the Louisville, Kentucky, area, is ~5 m thick at Sellersburg, Indiana. It consists of alternating pale buff gray, argillaceous, blocky dolostone beds, which carry only very sparse body fossils and burrows, alternating with light-gray limestone with wacke- to packstone fabrics that contain abundant thin laminar stromatoporoids, favositid, heliolitid, and halysitid corals, crinoid debris, brachiopods, and other fossils. These beds typically contain alternating thin bands of bluish-gray to cream-colored chert.

The Wabash Formation has primarily been studied in the central and northern part of Indiana (e.g., Pinsak and Shaver, 1964; Rexroad et al., 1978), where it is divided into the Mississinewa and Liston Creek members. The Wabash present in southern Indiana is believed to be a calcareous lateral equivalent of the Mississinewa Member. Throughout this region, the Wabash and even most of the Louisville Limestone are truncated beneath Devonian strata; only four exposures (quarries) of the Wabash are currently known in southern Indiana.

The Wabash Formation is somewhat constrained to the lower Ludlow by the occurrence of the brachiopod Kirkidium and the graptoloid Monograptus bohemicus in the (lower) Mississinewa Shale Member in northern Indiana (Berry and Boucot, 1970). Conodonts further bolster this interpretation (Rexroad et al., 1978). A thin K-bentonite near the base of the Wabash Formation has yielded zircons, which are being processed for U/Pb dating.

Middle Devonian

The Louisville, Kentucky, and Falls of the Ohio (Clarksville, Indiana) area is one of the classic exposures of Middle Devonian rocks in North America (Fig. 6). Although the succession is thin and incomplete, with numerous unconformities, the fossils are exceptionally diverse and well preserved, with silicified remains weathering freely from the limestones in immense quantities. Studies of these faunas include some of the earliest descriptions of fossils in the United States (Rafinesque and Clifford, 1820, and Leseur, 1821, published prior to the naming of the Devonian System by Sedgewick and Murchison, 1839). Documentation of taxonomy and paleoecology of these diverse invertebrate faunas, especially corals, has continued for nearly 200 years (Davis, 1887; Nettelroth, 1889; Girty, 1898; Savage, 1930; Oliver, 1960; Stumm, 1964; Conkin and Conkin 1976, 1980; Bulinski, this study). Similarly, their stratigraphy, sedimentology, and depositional environments have been documented in numerous studies (Perkins, 1963; Stumm, 1964; Kissling and Lineback, 1967; Droste and Shaver, 1975, 1986a, 1986b, 1986c, 1986d, 1986e; Conkin and Conkin, 1975, 1976, 1980; Conkin et al., 1973, 1976, 1998).

The entire local Devonian succession spans from the late Emsian to the late Famennian, some 40 million years, with the Middle Devonian being the focus of the present studies. The Devonian succession in the region commences above one of the most famous mapped disconformities, the Louisville paraconformity, remarkable in its featureless and nearly cryptic expression and yet reflecting more than 30 million years of erosion and non-deposition. It is a local manifestation of one of the great boundaries in North American stratigraphy, the Wallbridge unconformity used by Sloss (1963) to divide his Tippecanoe and Kaskaskia megasequences. A second distinctive, though less temporally significant (less than 1–3 million years), unconformity separates the fossil-rich Middle Devonian (Eifelian-Givetian) Jeffersonville and Sellersburg (North Vernon) carbonate and calcareous mudstone from the sparsely fossiliferous dark brownish-gray, green, and black shale succession of the New Albany Formation (New Albany Shale; upper Givetian to Famennian). The latter is arguably one of the most important petroleum source rocks in the Illinois Basin and its facies have received intensive study (see Lineback, 1968, 1970; Cluff et al., 1981; Schieber and Lazar 2004; Nuttall, 2013).

Recent work has attempted to correlate the sequences and bioevents recorded in the Louisville area with Eifelian to Givetian sequences in the Appalachian Basin (Fig. 6). Thin and incomplete representatives of about six sequences have been identified (Brett et al., 2011), though new data on conodonts and detailed studies of sequence stratigraphy in Kentucky and Indiana have raised important questions about the precise synchroneity of bioevents and/or biostratigraphic zonations (Brett et al., 2018b). However, to a first approximation, the major sea-level and biotic events recognized in the Appalachian Basin are also recognized on the western flank of the Cincinnati Arch, suggesting extrinsic, possibly global causes. Aspects of this complex and interesting stratigraphy and paleoecology are summarized below.

Louisville Paraconformity (Wallbridge Unconformity)

The Silurian strata near southeastern Indiana extend no higher than the Wabash Formation, as higher units, if once present, have been truncated by the Louisville paraconformity or Wallbridge unconformity of Dennison and Head (1975). This exemplar of a paraconformity is a nearly planar contact of two carbonates (packstone/rudstone) of similar color and weathering characteristics: the Louisville or Wabash formations of Silurian (Ludlow) age and the overlying Jeffersonville Limestone of Middle Devonian (latest Emsian to Eifelian) age. Both under- and overlying units may be rich in corals, but whereas the Louisville and Wabash have abundant syringoporids, small favositids, and Halysites, the Jeffersonville contains the large rugose corals and Favosites of the famed Falls of the Ohio coral bed. Thus, this contact, which represents a hiatus of 30–35 million years, is often surprisingly difficult to locate in the field. Its uniform topography was probably created during transgressive ravinement associated with the Devonian sea-level rise.

Sequences Eif-1 and Eif-2: Jeffersonville Formation

The Jeffersonville Formation (or Jeffersonville Limestone) comprises roughly 11 m of fossiliferous limestone, primarily packstone and grainstone with minor chert (Droste and Shaver, 1986c; Fig. 6). These beds are exceptionally well exposed at the Falls of the Ohio in Clarksville, Indiana, and adjacent Louisville, Kentucky. North of the Louisville area, the Jeffersonville interfingers with dolomitic peritidal facies (Geneva Dolostone; see Droste and Shaver, 1986b; Hendricks et al., 1994) and is mapped as a part of the Muscatatuck Group. The unit is of latest Emsian to early Eifelian age based upon conodonts, the majority being assigned to the costatus Zone (Orr, 1971). It represents the initial transgression of the Kaskaskia Megasequence.

In the Falls of the Ohio region, the Jeffersonville is divided into informal subunits, some regionally traceable (Perkins, 1963). At the base is a 2.5–3 m interval of pinkish-gray crinoidal rudstone, grainstone, and packstone that contains abundant, diverse, and large tabulate and rugose corals including some of the largest known solitary rugosans: Siphonophrentis gigantea, up to nearly a meter long and exceeding 10 cm in diameter. Conkin et al. (1998) divided this so-called “Coral Zone” into lower and upper subzones. The lower 1.5 m, which contains distinctive solitary rugosans (e.g., Aemulophyllum exiguum, Homalopyllum ungulum) and the largest hemispherical heads of the favositid Emmonsia, is considered by Oliver (1958) to be of late Emsian age. The upper coral subzone, slightly less than a meter thick, contains very large flattened stromatoporoids (up to 2 m in diameter), large colonial rugosans (Acinophyllum, Prismatophyllum), favositid tabulates, and stromatoporoids, some overturned. Stumm (1964) reviewed the fauna and synonymized many previously used names, but still recognized more than 200 species at the Falls of the Ohio (see Hendricks et al., 1994, for excellent illustrations, and “Paleoecology of the Jeffersonville Limestone Coral Zone biostrome at the Falls of the Ohio” section, for review).

The Coral Zone is gradationally overlain by the roughly 2-m-thick Amphipora ramosa Zone characterized by abundant medium-sized branching and head corals and thin, mat-like stromatoporoids, including the unusual ramose form Amphipora ramosa, packed in a fine-grained grainstone matrix.

This subunit is abruptly overlain by a darker-gray, fine-grained and somewhat argillaceous wackestone to packstone with thin bands of pale gray to cream-colored chert that is packed with silicified valves of the small spiriferid brachiopod Brevispirifer gregarius, as well as the “kneecap” coral Favosites turbinatum, small solitary rugose corals (especially the claw-like Zaphrentis phrygia), and the large gastropod Turbinopsis. It also contains the zonally significant charophyte Moellerina greenei, which has been correlated into northern Indiana and Ohio. This distinctive marker interval, termed the Brevispirifer gregarius Zone, can be traced widely. It occurs in the middle (unit F) of the correlative Columbus Limestone of Ohio and retains its identity northward in Indiana, where it is both underlain and overlain by peritidal dolomitic carbonates. The Brevispirifer Zone is interpreted as an offshore, low-energy facies, possibly associated with the “False Nedrow” of the upper Moorehouse sequence Eif-2 (Ver Straeten, 2007). A silicified zone near the top of this unit was identified by Conkin et al. (1998) as the Onondaga Indian Nation, or “Tioga B,” K-bentonite of New York, which has been precisely dated at 390 ± 0.5 Ma (Roden et al., 1990; Tucker et al., 1998; Ver Straeten, 2004). On this basis, Brett et al. (2011) suggested that the Brevispirifer Zone marks a pulse of transgression near the base of sequence Eif-2 and overlies a cryptic sequence boundary. This is further suggested by the fact that in the Louisville area, Conkin et al. (2005) demonstrated that this zone locally oversteps the Amphipora and Coral Zone to rest directly on the Silurian Louisville Formation at one location.

The Brevispirifer Zone is followed by the Bryozoan-Brachiopod Zone, a more highly fossiliferous, somewhat cherty interval of crinoidal packstone to grainstone that contains a diverse fauna of solitary rugosans, fenestrate and Coscinotrypa bryozoans, brachiopods (Megastrophia sp., Strophodonta demissa, Pholidostrophia, and atrypids), and the blastoid Elaeocrinus (which, under a former name, gave rise to an older term for this interval, the “Nucleocrinus Zone”). This interval and the overlying Paraspirifer Zone would seem to record somewhat deeper shelf conditions than the Brevispirifer Zone, suggesting continued transgression equivalent to the Seneca Member in New York. To the north, this zone may be replaced laterally by the peritidal fenestral micrites of the Vernon Fork Member.

The uppermost 2–3 m of the Jeffersonville Formation records a more widespread interval, the upper Paraspirifer Zone. This highly fossiliferous light pinkish-gray pack- to grainstone contains a diversity of brachiopods, typically replaced by white silica. These are characterized by a fauna like the underlying beds, but with an abundance of the large spiriferid Paraspirifer acuminatus in addition to Megastrophia sp., Strophodonta demissa, Pholidostrophia, and atrypids. Phacopid trilobites as well as fenestrate and Sulcoretepora bryozoans are also common, as are the blastoid Heteroschisma and various crinoid columnals and plates, especially those of the camerate Dolatocrinus. In weathered outcrop these silicified fossils, typically bright orange in color, are found in residual terra rossa soils covering karst surfaces in the Jeffersonville.

The Paraspirifer Zone can be traced northward where it overlies the Vernon Fork Member and eastward into Ohio where it forms the uppermost unit of the Columbus Limestone. The epibole of Paraspirifer acuminatus even extends farther eastward into the Appalachian Basin, although this interval appears to be younger than occurrences in the Moorehouse Member of the Onondaga Limestone of New York. Based on lateral relationships and evidence for shallower facies than those of the Brevispirifer Zone, we tentatively interpret the Paraspirifer Zone as a later phase of the Eif-2 highstand.

Conkin and Conkin (1984) noted and correlated in detail several horizons of fragmentary fish bones within the Jefferson-ville, attributing them to minor discontinuities. We interpret these bone beds as minor condensed horizons associated with marine flooding surfaces. The most significant of these lies near the base of the overlying Sellersburg Formation.

Sellersburg Formation (North Vernon Formation)

The Jeffersonville Formation is sharply overlain by ~5–15 m of medium- to darker-gray argillaceous limestone and crinoidal grainstone known as the Sellersburg Formation in Kentucky and the North Vernon Formation in Indiana (Droste and Shaver, 1986d; ironically, the Sellersburg type section is in Indiana; we refer to the unit as the Sellersburg Formation). This formation is of latest Eifelian to Givetian age (Eif-2 to Giv-3?) and thus it coincides with the famed Hamilton Group of the Appalachian Basin, although exact chronostratigraphic relationships are still debated.

Sequence Eif-2/Eif-Giv: Speed Member of the Sellersburg Formation

A thin (0.1–4.5 m) interval of highly fossiliferous, phosphatic, dark-gray argillaceous limestone sharply overlies the Jeffersonville Formation in southern Indiana (Fig. 6). This unit is termed Speed (or Speeds) Member (Droste and Shaver, 1986f) for its typical occurrence in quarries at Speed, Indiana, and assigned to the base of the Sellersburg or North Vernon Formation (Droste and Shaver, 1986d). This shaly limestone contains small, black, phosphate-impregnated clasts and sporadic glauconite, suggesting strong condensation. Locally these basal lag beds fill small scour channels on top of the Jeffersonville, suggesting a regional unconformity associated with a sediment-starved flooding surface, perhaps the Eif-2 maximum flooding surface. Notably, this lag contains abundant saber-like onychodont fish teeth. A similar thin bone bed with onychodont teeth occurs near the Onondaga-Marcellus boundary in New York (see Baird and Brett, 1991) and is interpreted as roughly coeval with the basal Speed lag (DeSantis and Brett, 2007, 2011; Brett et al., 2011). Conkin and Conkin (1975, 1984) and Conkin et al. (2005) correlated a thin silica-rich zone near the base of the Speed Member with the widespread Tioga K-bentonite of the Appalachian Basin, further supporting this interpretation.

The rich fossil content of this interval is reminiscent of the fauna of the middle Delaware Formation of central Ohio and includes the small rugose “button coral” Hadrophyllum dorbignyi, crinoid columnals, and the brachiopods Athyris cf. fultonensis, Rhipidomella vanuxemi, Schizophoria sp., Strophodonta cf. demissa, and Leptaena “rhomboidalis.” The shells are mainly disarticulated and many are fragmented and/or corroded. Thus, the Speed Member is interpreted as an extremely condensed equivalent of the upper Eifelian Delaware Formation and represents a thin vestige of the highstand of depositional sequence Eif-2 and almost the entirety of Eif-Giv (the lower Marcellus sequence, which spans the Eifelian-Givetian boundary). The Speed is correlated with the dark shale and thin tabular carbonate of the Dublin Member of the Delaware Formation in Ohio, and its lateral equivalent in the Union Springs and lower Oatka Creek formations (Marcellus Shale subgroup) in the Appalachian Basin (DeSantis and Brett, 2007, 2011; Brett et al., 2011).

Sequence Eif-Giv: Silver Creek Member of the Sellersburg Formation

The overlying Silver Creek Member, which ranges from 0.5 to 8 m thick, comprises medium-gray to pale gray argillaceous limestone and dolostone (Conkin et al., 1973, 1976; Droste and Shaver, 1986e). Cream-colored chert nodules, often following burrows, are typical near the top of the unit (locally called the New Chapel chert). The mudstone is typically heavily bioturbated and weathered surfaces reveal evidence of Zoophycos, Chondrites, and Planolites. Thin lenses and stringers of concentrated shell and bryozoan debris occur within the Silver Creek. These skeletal hash layers probably represent storm winnowed lag beds and contain abundant small brachiopods, especially “Chonetes” yandellanus, Ambocoelia cf. umbonta, Cyrtina sp., Mucrospirifer (Alatiformia) sp., and the atrypid Pseudoatrypa, commonly with spirallia preserved via silicification. Other taxa include Sulcoretepora bryozoans, Eldredgeops trilobites, and mollusks such as nuculid bivalves, Modiomorpha concentrica, Paracyclas sp., Palaeoneilo spp., as well as the gastropod Bembexia sulcomarginata. The latter is restricted to the lower Givetian lower Hamilton Group in the Appalachian Basin, and suggests correlation of the Silver Creek Member with the Oatka Creek Formation (upper Marcellus), although conodont data are sparse and non-diagnostic. To the north of the Louisville area, the lower Silver Creek is locally exceptionally rich in spiriferid brachiopods Orthospirifer, Mediospirifer, and Mucrospirifer (Alatiformia), and atrypids; this facies was termed the Deputy Member by Campbell (1942). The Silver Creek has also yielded placoderm plates and occasional articulated heads of Macropetalichthyes.

The argillaceous Silver Creek interval represents the highstand systems tract (HST) of sequence Eif-Giv (DeSantis and Brett, 2007, 2011; Brett et al., 2011). This major influx of siliciclastic mud onto the craton was associated with the onset of the second tectophase of the Acadian orogeny. This interval may be correlated with the upper cherty Delaware Formation in Ohio, the Chittenango Black Shale Member of the Oatka Creek Formation in the Appalachian Basin, and the Bell Shale in the Michigan Basin.

Sequence Giv-1: Swanville Member of the Sellersburg Formation

The upper beds of the Silver Creek Member locally pass abruptly upward into a pale packstone and grainstone, termed the Swanville Member by Campbell (1942). This unit contains abundant brachiopods, especially the widespread orthid brachiopod Tropidoleptus carinatus, Devonochonetes coronatus, and “Orthospirifer” euryteines. This triad of brachiopods, representing an important faunal incursion, is widely recognizable throughout the Midwest, including the basal “Blue Limestone” beds of the Silica Formation in northern Indiana and Ohio. Bartholomew and Brett (2007) and Brett et al. (2011) correlated the lenticular Swanville with the Stafford-Mottville Member in the Appalachian Basin, making it the TST of sequence Giv-1. This unit is erosionally removed at a significant unconformity beneath the Beechwood Limestone Member at many sites. Strangely, it is present mainly in sections where the latter is lacking, perhaps owing to later erosional truncation. These sites may represent areas where the Swanville Member lay in erosional pockets that escaped subsequent peneplanation during the sub-Beechwood lowstand.

Sequence Giv-2? to Giv-3?: Beechwood Member of the Sellersburg Formation

The Beechwood Member of the Sellersburg Formation (Butts, 1915; Conkin et al., 1973, 1976; Droste and Shaver, 1986a) rests sharply on underlying beds and in places erosional truncation of subjacent strata is evident. The significance of this unconformity becomes increasingly evident south of Louisville, Kentucky, where the entire Sellersburg and Jeffersonville formations have been removed and typical Beechwood rests directly on the Silurian Louisville Formation at an irregular unconformity (Droste and Shaver, 1986f).

Up to 3 m thick, the Beechwood is a composite unit with two main divisions, each commencing with a phosphatic bed interpreted as a basal transgressive lag deposit. The base of the member is particularly striking with cobble-sized, phosphate-impregnated clasts of dolomitic carbonate, some encrusted by bryozoans. These clasts are embedded in a matrix of coarser crinoidal grainstone with quartz sand grains (Orr and Pollock, 1968; this is bone bed 12 of Conkin et al., 1998). The overlying limestone is exceptionally rich in fossils and contains a diverse fauna of corals, brachiopods, bryozoans, trilobites, blastoids, and crinoids. Calyces and “cogwheel columnals” of Dolatocrinus are particularly notable in the lower Beechwood (Cooper et al., 1942; see Brett et al., 2011).

At some localities, a middle interval of shaly limestone carries a profusion of the small spiriferid Ambocoelia umbonata. The overlying upper submember, another fossiliferous packstone, also features a basal phosphatic limestone and the sharp lower contact of this unit is another erosion surface. Both lower and upper phosphatic clast limestones of the Beechwood Member are interpreted as basal lowstand/early transgressive lag beds overlying sequence boundaries. Although possibly diachronous with respect to basal TST skeletal limestones in the foreland basin, these two divisions have been tentatively related to the TSTs of the Ludlowville and Moscow formations (the Center-field and Tichenor members, respectively). Unlike those more basinal successions, local highstand deposits are thin and probably largely removed by later erosion. However, they may be represented in thin Ambocoelia-rich beds (as in the case of the middle shaly unit).

Nearly all species present in the lower Beechwood fauna are common to the lower to middle Hamilton Group of the Appalachian Basin, and distinctive macrofossil elements such as Fimbrispirifer divaricatus and Ancyrocrinus are typical of, or even restricted to, the lower Hamilton in the Appalachian Basin. At least the lower unit of the Beechwood has long been correlated with the widespread Centerfield Limestone of New York. However, recent conodont studies reported in Brett et al. (2018b) suggest that all the Beechwood in its type area falls into the middle Givetian middle varcus Zone (now Polygnathus ansatus Zone), although probably not including the upper, Tully-equivalent, part of that zone. This would imply that the unit is entirely equivalent to the Moscow Formation, which is problematic both in terms of sequence stratigraphy and macrofauna. Future research will attempt to resolve these discrepancies.

Phosphatic lag beds at the top of the Beechwood Member have yielded different conodont assemblages in different localities, with middle varcus Zone (high ansatus Zone) elements found at the Sellersburg Quarry, whereas other sites have yielded both reworked middle varcus elements and conodonts as young as the late Givetian cristatus-ectypus to disparilis zones or even rare early Frasnian Ancyrodella (Orr and Pollock, 1968; see summary in Brett et al., 2018b). These lags provide a testament to prolonged sediment starvation during the late Givetian to earliest Frasnian interval.

Taghanic Unconformity

The top of the Beechwood is irregular and locally the entire member is truncated such that overlying Blocher Member of the New Albany Shale rests directly on the upper beds of the Silver Creek Member. The Sellersburg Quarry once exposed a pocket of probable residual reddish-brown silicified fossils at this level, roofed by a layer of hard black shale. This brownish unconsolidated clay unit is interpreted as a residual paleosol preserved in a small solution feature on the karst erosion surface. The irregular surface and putative paleosol reflect a short-lived but strong low-stand within the Middle Devonian (upper ansatus Zone), during which older carbonate deposits underwent karst processes. We equate this sharp contact with the Taghanic unconformity that underlies the Tully Limestone in the Appalachian foreland basin (New York and Pennsylvania; see Brett et al., 2003b; Baird and Brett, 2008; Baird et al., 2012; Zambito et al., 2012, 2016) and laterally equivalent Portwood Formation in Kentucky (Brett et al., 2018b). This unconformity divides the Kaskaskia Mega-sequence into two subintervals.

Sequence Giv-5: Blocher Member of the New Albany Shale

In sharp contrast to the carbonates below, the overlying unit comprises black, platy, organic-rich shale: the basal or Blocher Member of the New Albany Shale (Campbell, 1946; Lineback 1968, 1970). A thin (~10 cm) basal lag deposit including green glauconitic stained dolomitic carbonate clasts, quartz sand grains, phosphatic nodules, and sparse fish bones (including onychodont fish teeth) rests on the underlying limestone surface. It is capped by a crust of euhedral pyrite at the sharp contact with the overlying black shale. This contact is a maximum starvation surface (MSS) associated with major eustatic/tectonic sea-level rise (cf. Baird and Brett, 1991).

The overlying black shale contains meager fauna of small lingulid and orbiculoid brachiopods, as well as rare fish bones and wood fragments. These dysoxic to anoxic facies represent a major tectonic and eustatic induced transgression, forming an early highstand systems tract associated with the widespread Taghanic Onlap (Johnson, 1970). The mud is a distal record of a major influx of siliciclastics originating from the third and most significant tectophase of the Acadian orogeny (Ettensohn, 1992a, 1992b). The Blocher Member has yielded conodonts of the hermanni and disparilis zones (Over, 2002), indicating a late Givetian age, roughly equivalent to the Geneseo Formation of New York. We regard it as the strong highstand phase of sequence Giv-5 (Brett et al., 2011).

SUMMARY DISCUSSION

The Paleozoic succession of the Louisville region is readily divisible into 3rd-order depositional sequences, as well as smaller 4th-order cycles (Figs. 3-6). We have refined the Upper Ordovician Cincinnatian Series sequence stratigraphic classification originally put forward by Holland and Patzkowsky (1996), clarifying existing sequence boundaries and recognizing several new regionally angular unconformities that have resulted in sequence splitting and renumbering (Brett et al., 2015b, 2018a; Fig. 4). The succession begins with the C1 (Kope Formation; Edenian) and C2 (Fairview Formation; basal Maysvillian) sequences, followed by the more limestone-rich C3 sequence (Bellevue and Corryville members of the Grant Lake Formation). The Mount Auburn Member of the Grant Lake is newly recognized as the TST of sequence C4, with the lower Richmondian Arnheim Formation, forming the C4 HST. The old C5 sequence has been radically revised based on the discovery of a major erosional surface within Waynesville Formation–equivalent strata (Rowland formation, as used herein) in Kentucky, the mid-Richmondian unconformity (Brett et al., 2015b) and higher disconformities. The lower to middle Waynesville/Rowland (Fort Ancient and Clarksville member equivalents) is considered to represent the new C5 sequence, whereas the upper Waynesville/Rowland formations (Blanchester Member equivalent) and Liberty/Bardstown formations comprise a revised C6 sequence. The C7 sequence consists of much of the Whitewater Formation (and equivalent strata to the south). Finally, an uppermost Cincinnatian C8 sequence (mostly the same as the old C6) is represented by the uppermost Whitewater Formation and Elkhorn Formation. A megasequence boundary, the Cherokee unconformity, separates the Upper Ordovician from the Silurian above.

The basal Silurian sequence S-I, extended from the work of Brett et al. (1990, 1998), consists of most of the Brassfield Formation sensu stricto on the east side of the Cincinnati Arch; it may or may not be present on the west side, as the western golden Brassfield is likely younger than the type Brassfield, equivalent to the Oldham Limestone of central Kentucky. S-II is made up of the upper Brassfield, Plum Creek Shale, Oldham Limestone, and Lulbegrud Shale in eastern Kentucky; the golden Brassfield is believed to represent S-II in western Kentucky and Indiana. S-III is represented by the Lee Creek Formation (equivalent to the Waco Member of north-central Kentucky), and S-IV consists of the Osgood Formation and correlative Estill Shale on the western and eastern sides of the Cincinnati Arch, respectively. The equivalents of the higher S-V and S-VI sequences (Figs. 5, Fig. 6), while readily recognizable along the southeastern Cincinnati Arch (foreland basin) sections, are somewhat more controversial on the western side. Brett and Ray (2005) and McLaughlin and Brett in McLaughlin et al. (2008b) identify the Lewisburg Formation (the mid-Osgood carbonate of earlier workers) and overlying Massie Shale as equivalents of S-V Irondequoit and Rochester formations, while conodont and carbonate carbon isotope studies of Cramer and Kleffner (also reported in McLaughlin et al., 2008b) suggest that these units may instead belong to S-VI, making them equivalent to parts of the Lockport Group of New York. Ongoing work is directed toward the resolution of this dilemma.

In the Middle Devonian, Eifelian sequences Eif-1 and Eif-2 are identified within the Jeffersonville Formation and separated by a cryptic, but regionally angular disconformity below the Brevispirifer gregarius Zone (Fig. 6). The highstand of Eif-2, recorded in the lower Marcellus or Union Springs Formation (Ver Straeten, 2007; Brett et al., 2011) of the Appalachian Basin and present in the lower Delaware Formation in Ohio, is absent or very strongly condensed at the basal phosphatic bone bed of the Speed Member of the Sellersburg Formation (North Vernon Formation). However, an equivalent of the upper Marcellus Oatka Creek Formation (Eif-Giv of Brett et al., 2011, so-named as it spans the Eifelian-Givetian boundary) is recorded in the Hadrophyllum-rich beds of the Speed, interpreted as the TST, equivalent to a similar Hadrophyllum bed in the Delaware Formation of Ohio (DeSantis and Brett, 2007, 2011), and the overlying, argillaceous limestone of the Silver Creek Member. A thin and lenticular vestige of sequence Giv-1 may be present in the Swanville Member of Campbell (1942), and the overlying Beechwood Member may record the stacked, condensed remnants of Giv-2 and Giv-3 (Brett et al., 2011, 2018b). An unconformity at the top of this carbonate succession and a shift to dark-gray to black pyritic shale (the Blocher Member of the New Albany Formation) may reflect the major Taghanic unconformity and Taghanic (Geneseo) transgression of the late Givetian in the Appalachian Basin, but several of these correlations require further testing.

The widespread distribution of these sequences permits their use as approximate chronostratigraphic units to facilitate correlation in multiple basins and, locally, across state lines. Although not perfect (diachronous correlations and local variations are possible and even expected), these cycles, particularly those of decameter scale, offer the tantalizing possibility of establishing an extremely high-resolution stratigraphic understanding of the North American, and perhaps global, geologic record.

FIELD TRIP: GEOLOGY AND PALEONTOLOGY OF THE WESTERN CINCINNATI ARCH NEAR LOUISVILLE, KENTUCKY

This two-day field trip showcases the Upper Ordovician, Silurian, and Middle Devonian strata of the greater Louisville area; younger rock may be encountered in passing. Stops follow an ascending stratigraphic order where possible to improve the sense of a narrative, although some “time traveling” is unavoidable due to the geographic availability of outcrops. Some localities have been selected to feature fresh exposures and new findings, particularly those related to our revised sequence stratigraphic interpretation of the Cincinnatian. Others are older and already documented in the literature, but critical to the understanding of the regional geologic history. Certain units are richly fossiliferous limestone and shale, bursting with brachiopods, bryozoans, sponges, or corals, whereas others are mostly barren and interesting in their own way. Wide-ranging discussions at selected stops will cover approaches to paleoenvironmental interpretation, the stratigraphic context of reefs and biostromes, proximal and distal comparisons of facies, and the local manifestation of global biotic and geochemical events, including major carbonate carbon isotope excursions.

Day 1: Upper Ordovician and Silurian Strata along U.S. Highway 31E/U.S. Highway 150

Christopher B.T. Waid, Kyle R. Hartshorn, and Carlton E. Brett

The first day of the field trip explores a transect along U.S. Highway 31E/U.S. Highway 150 south of Louisville, near Mount Washington, Kentucky (Fig. 7). This highway, already replete with outcrops, was recently the subject of construction, with a major section of the road rerouted just south of the Salt River. This resulted in roughly nine new roadcuts, including several of moderate size (with two or three benches). We assign these new outcrops letter designations, starting with Outcrop A for the northernmost outcrop and proceeding along the alphabet as one goes southward (note that stops have their own designations; see Fig. 7). These informal names are intended to help with wayfinding during the excursion, as the actual itinerary crosses back and forth along the route to maintain ascending stratigraphic order.

Figure 7.

Regional geological map of the Mount Washington, Kentucky, area showing the location outcrops to be visited during Day 1. The small black numbers are stop numbers; “opt” indicates an optional stop. Abbreviations: Dol—Dolostone; Fm—Formation; KGS—Kentucky Geological Survey; Ls—Limestone; Sh—Shale.

Figure 7.

Regional geological map of the Mount Washington, Kentucky, area showing the location outcrops to be visited during Day 1. The small black numbers are stop numbers; “opt” indicates an optional stop. Abbreviations: Dol—Dolostone; Fm—Formation; KGS—Kentucky Geological Survey; Ls—Limestone; Sh—Shale.

All the new outcrops expose the Upper Ordovician Cincinnatian Series, ranging from the uppermost Maysvillian Stage (middle Cincinnatian; lower upper Katian, Ka2) through the Richmondian Stage (upper Cincinnatian; upper Katian, Ka2–Ka4). The full regional succession includes the Grant Lake Formation (Corryville and Mount Auburn members; respectively the HST of sequence C3 and the TST of sequence C4), the Arnheim Formation (locally mapped as the uppermost Grant Lake Formation or Bull Fork Formation; the HST of sequence C4), the Rowland Formation (locally mapped as the Rowland Member of the Drakes Formation; sequences C5 and C6, in part), the Bardstown formation (locally mapped as the Bardstown Member of the Drakes Formation; sequence C6, in part), and the Whitewater Formation (especially the Saluda Member, locally mapped as the Saluda Member of the Drakes Formation; sequence C7). The correlation and sequence stratigraphy of these units will be discussed in detail.

Afterwards, the trip will visit several complementary outcrops to the north, near Mount Washington proper (Fig. 7). These roadcuts expose the middle to upper Richmondian, the Ordovician-Silurian boundary, and much of the regional Silurian succession (including Brassfield, Lee Creek, Osgood, Lewisburg, Massie, and Laurel formations; sequences S-II through S-VI), providing an excellent primer on these slightly younger strata.

Road Log

Day 1’s road log begins and ends at I-265 Exit 17 (for Mount Washington). The entire excursion is spent on U.S. Highway 31E/U.S. Highway 150 between Mount Washington and Coxs Creek, Kentucky. Brief descriptions are provided within the road log for stops and other outcrops. Note that a lunch stop at Broad Run Park is planned but not included in the road log mileage (due to the proximity of all the day’s sections, the exact timing of lunch can be ad hoc). All distances are given in miles.

Cum. mileageMileageDescription
0.00.0Take Exit 17 from I-265 (the Gene Snyder
Freeway) then turn south onto U.S. Highway
31E/U.S. Highway 150/Bardstown
Road (henceforth U.S. 31E); note extensive
outcrops of the Louisville Limestone
around the interchange.
3.03.0Pass Thixton Lane (to the west), marking
the town of Thixton, Kentucky.
3.20.2Beginning of a section of Silurian on both
sides, with the massive Laurel Dolostone
overlying the Massie, Lewisburg, and
Osgood formations; this is the upper end
of Stop 1-8.
3.70.5Lower end of the Thixton roadcut; here the
Upper Ordovician Saluda Member of the
Whitewater Formation is overlain by the
Silurian Brassfield, Lee Creek, and overlying
maroon and green shales of lower
Osgood Formation (notable for their similarity
to the mostly correlative Estill Shale
on the east side of the Cincinnati Arch);
this is the lower part of Stop 1-8.
3.80.1Outcrop on the west side of the road,
across from Bardstown Bluff, exposing
the upper Bardstown and/or lower Whitewater
Formation.
4.10.3Pass the entrance to Broad Run Park (to the
east); this is the lunch stop; the park contains
a stream bank and waterfall outcrops
of Rowland, Bardstown, and Whitewater
strata, particularly along the Limestone
Gorge Trail, but there will not be time to
visit them during this field trip.
4.20.1Cross the bridge over Floyds Fork.
4.50.3Outcrop of Rowland Formation on the left
(east) side of the highway.
4.90.4Cross the Jefferson/Bullitt County line just
south of junction with Kentucky Route
660, entering Bullitt County.
5.20.3Outcrop of Bardstown Formation on left
(east) at junction with U.S. 31EX (N.
Bardstown Road); begin long roadcut of
Bardstown through Laurel (Stop 1-7).
5.70.5Upper end of Stop 1-7, showing the Silurian
part of the section (Brassfield, Lee
Creek, Osgood, Lewisburg, Massie, and
Laurel formations).
6.81.1Travel through the outskirts of Mount
Washington, passing junction with Kentucky
Route 44.
7.30.5Outcrop of Whitewater Formation
(Buckner-Saluda) on the right (west).
7.80.5Outcrops of Rowland formation (?) along
Whittaker Run on the right (west) side of
the road, just north of the junction with
(U.S.) S 31E Loop on the left (east).
8.00.2Outcrop of Fisherville submember (lower
member of Rowland) overlain unconformably
by upper member of Rowland
(Stop 1-6).
8.20.2Outcrop of upper Arnheim Formation
overlain by probable South Gate Hill bed
at base of the Waynesville-equivalent lower
Rowland shales (the C4/C5 boundary of
Holland and Patzkowsky, 1996).
8.70.5Ledgy limestone in Whittaker Run on the
west side of the highway.
9.50.8High outcrop on left (east) in the Grant
Lake and Arnheim formations, the latter
containing Leptaena and Rhynchotrema.
9.90.4Roadcut on the left (north) exposing Grant
Lake Formation (with prominent, ledge-forming
grainstone of the Mount Auburn
Member) and Arnheim Formation; very
rich in the brachiopods Vinlandostrophia
ponderosa and Hebertella spp. A
1.5-m-thick, phosphatic grainstone near
the bridge may be the Flemingsburg bed, a
distinctive limestone marker mapped on
the east side of the Cincinnati Arch.
10.00.1Cross bridge over the Salt River, which
marks the Bullitt/Spencer County line;
immediately thereafter, in Spencer County,
begin following the new section of U.S.
31E/U.S. 150 completed in 2017.
10.70.7North end of a large, fresh roadcut starting
in the rubbly gray limestones of the upper
Grant Lake Formation (outcrop A); pull off
for Stop 1-1.
Cum. mileageMileageDescription
0.00.0Take Exit 17 from I-265 (the Gene Snyder
Freeway) then turn south onto U.S. Highway
31E/U.S. Highway 150/Bardstown
Road (henceforth U.S. 31E); note extensive
outcrops of the Louisville Limestone
around the interchange.
3.03.0Pass Thixton Lane (to the west), marking
the town of Thixton, Kentucky.
3.20.2Beginning of a section of Silurian on both
sides, with the massive Laurel Dolostone
overlying the Massie, Lewisburg, and
Osgood formations; this is the upper end
of Stop 1-8.
3.70.5Lower end of the Thixton roadcut; here the
Upper Ordovician Saluda Member of the
Whitewater Formation is overlain by the
Silurian Brassfield, Lee Creek, and overlying
maroon and green shales of lower
Osgood Formation (notable for their similarity
to the mostly correlative Estill Shale
on the east side of the Cincinnati Arch);
this is the lower part of Stop 1-8.
3.80.1Outcrop on the west side of the road,
across from Bardstown Bluff, exposing
the upper Bardstown and/or lower Whitewater
Formation.
4.10.3Pass the entrance to Broad Run Park (to the
east); this is the lunch stop; the park contains
a stream bank and waterfall outcrops
of Rowland, Bardstown, and Whitewater
strata, particularly along the Limestone
Gorge Trail, but there will not be time to
visit them during this field trip.
4.20.1Cross the bridge over Floyds Fork.
4.50.3Outcrop of Rowland Formation on the left
(east) side of the highway.
4.90.4Cross the Jefferson/Bullitt County line just
south of junction with Kentucky Route
660, entering Bullitt County.
5.20.3Outcrop of Bardstown Formation on left
(east) at junction with U.S. 31EX (N.
Bardstown Road); begin long roadcut of
Bardstown through Laurel (Stop 1-7).
5.70.5Upper end of Stop 1-7, showing the Silurian
part of the section (Brassfield, Lee
Creek, Osgood, Lewisburg, Massie, and
Laurel formations).
6.81.1Travel through the outskirts of Mount
Washington, passing junction with Kentucky
Route 44.
7.30.5Outcrop of Whitewater Formation
(Buckner-Saluda) on the right (west).
7.80.5Outcrops of Rowland formation (?) along
Whittaker Run on the right (west) side of
the road, just north of the junction with
(U.S.) S 31E Loop on the left (east).
8.00.2Outcrop of Fisherville submember (lower
member of Rowland) overlain unconformably
by upper member of Rowland
(Stop 1-6).
8.20.2Outcrop of upper Arnheim Formation
overlain by probable South Gate Hill bed
at base of the Waynesville-equivalent lower
Rowland shales (the C4/C5 boundary of
Holland and Patzkowsky, 1996).
8.70.5Ledgy limestone in Whittaker Run on the
west side of the highway.
9.50.8High outcrop on left (east) in the Grant
Lake and Arnheim formations, the latter
containing Leptaena and Rhynchotrema.
9.90.4Roadcut on the left (north) exposing Grant
Lake Formation (with prominent, ledge-forming
grainstone of the Mount Auburn
Member) and Arnheim Formation; very
rich in the brachiopods Vinlandostrophia
ponderosa and Hebertella spp. A
1.5-m-thick, phosphatic grainstone near
the bridge may be the Flemingsburg bed, a
distinctive limestone marker mapped on
the east side of the Cincinnati Arch.
10.00.1Cross bridge over the Salt River, which
marks the Bullitt/Spencer County line;
immediately thereafter, in Spencer County,
begin following the new section of U.S.
31E/U.S. 150 completed in 2017.
10.70.7North end of a large, fresh roadcut starting
in the rubbly gray limestones of the upper
Grant Lake Formation (outcrop A); pull off
for Stop 1-1.

Stop 1-1: Outcrop A—New U.S. 31E/U.S. 150 South of the Salt River in Spencer County, Kentucky

This outstanding fresh roadcut (Figs. 8, 9) begins with an 11-m-thick succession of the “Vinlandostrophia ponderosa zone” (Butts, 1915), tentatively assigned to the upper Corryville Member of the Grant Lake Formation, but considered to be correlative to the lower or Sunset Member of the Arnheim by Butts (1915), one of the last researchers to study this interval in detail. The basal interval comprises thin and poorly bedded shaly nodular gray packstone beds, rich in large V. ponderosa and Hebertella sp. brachiopods, as is typical of the uppermost Corryville Member. These beds are capped by a 1.5-m-thick massive, faintly orange weathering grainstone, herein tentatively assigned to the grainstone (Straight Creek) facies (Schumacher et al., 1991) of the Mount Auburn Member of the Grant Lake Formation. The sharp base of this conspicuously ledge-forming limestone is tentatively interpreted as the lower boundary of the redefined sequence C4, with the Mount Auburn as a condensed TST. However, it is also conceivable that this instead represents the 4th-order sequence boundary of C4B; i.e., making the grainstone a thick example of the Tilton submember of the Arnheim Formation (Brett et al., 2018a). Additional regional study is required to further constrain the identity of these beds.

Figure 8.

Labeled outcrop photo showing the units exposed at outcrop A (Stop 1-1). Note road for general scale.

Figure 8.

Labeled outcrop photo showing the units exposed at outcrop A (Stop 1-1). Note road for general scale.

Figure 9.

Stratigraphic column for Outcrop A (Stop 1-1), with base of section on the lower left. Note the tentative identity of the lower Vinlandostrophia ponderosa zone as the Corryville Member of the Grant Lake Formation. Third column gives third- and fourth-order sequence designations and systems tract interpretation. Abbreviations: HST—highstand systems tract; FSST—falling stage systems tract; LST—lowstand systems tract; TST—transgressive systems tract. L.—Leptaena; V.—Vinlandostrophia. Bar scale in meters.

Figure 9.

Stratigraphic column for Outcrop A (Stop 1-1), with base of section on the lower left. Note the tentative identity of the lower Vinlandostrophia ponderosa zone as the Corryville Member of the Grant Lake Formation. Third column gives third- and fourth-order sequence designations and systems tract interpretation. Abbreviations: HST—highstand systems tract; FSST—falling stage systems tract; LST—lowstand systems tract; TST—transgressive systems tract. L.—Leptaena; V.—Vinlandostrophia. Bar scale in meters.

The abrupt upper contact of the grainstone with the shaly nodular beds above represents a flooding surface and the base of Arnheim Formation. The typical Sunset Member (basal Arnheim) is missing, though that interval may be cryptically represented in the 1–2 m of beds overlying the grainstones of the Mount Auburn. This absence is anomalous within an otherwise predictable succession and requires additional study.

We assign the thick (~8 m) succession of medium-gray mudstone and muddy packstone to the Oregonia Member of the Arnheim Formation (C4 HST). This zone was mapped as the upper Grant Lake Formation by Kepferle (1976a), who recognized it as the Arnheim of older workers (particularly Foerste, 1912) but assigned it to the Grant Lake based on its nearly identical lithology. The Oregonia yields abundant small Vinlandostrophia cf. cypha, as well as less common Leptaena richmondensis. The latter brachiopod is an iconic member of the “Richmondian Invasion,” a late Cincinnatian bioevent characterized by an influx of non-native fauna into the basin. Leptaena and Rhynchotrema dentatum (known from correlative localities just north of the Salt River and likely present at this roadcut as well) seem to have been the vanguards of this invasion. Easily identifiable and widely distributed across both sides of the Cincinnati Arch, their cooccurrence (sometimes, as here, mixed with rare V. ponderosa) is a reliable biostratigraphic indicator for the Oregonia.

Higher beds visible near the top of the section belong to the basal Rowland Formation, which is better exposed at subsequent stops.

Cum. mileageMileageDescription
11.00.3Outcrop B, a long exposure of Rowland
formation; we will visit this section later as
Stop 1-3.
11.30.3Outcrop C, featuring a low outcrop of
upper Rowland.
11.40.1Pass junction with Kentucky Route 48.
11.70.3Upper end of a long cut (outcrop D) in the
lower to middle Rowland (we will walk
back up to this exposure); the south end
of the outcrop is near the Bullitt/Spencer
County line.
11.80.1Gap in outcrop; the east side of the road is
just west of a triple point between Bullitt
(west), Nelson (south), and Spencer (northeast)
counties; the road passes through
Bullitt County for less than 100 m before
entering Nelson County.
11.90.1Beginning of a large, high roadcut (outcrop
E); pull over near sign and continue along
the shoulder to the base of the outcrop.
12.00.1Passengers disembark for Stop 1-2A;
vehicles will proceed to Rummage Road (just
to the south), turn around, and drive back
~0.3 mi uphill (north) to reload passengers
at the top of Stop 1-2B.
Cum. mileageMileageDescription
11.00.3Outcrop B, a long exposure of Rowland
formation; we will visit this section later as
Stop 1-3.
11.30.3Outcrop C, featuring a low outcrop of
upper Rowland.
11.40.1Pass junction with Kentucky Route 48.
11.70.3Upper end of a long cut (outcrop D) in the
lower to middle Rowland (we will walk
back up to this exposure); the south end
of the outcrop is near the Bullitt/Spencer
County line.
11.80.1Gap in outcrop; the east side of the road is
just west of a triple point between Bullitt
(west), Nelson (south), and Spencer (northeast)
counties; the road passes through
Bullitt County for less than 100 m before
entering Nelson County.
11.90.1Beginning of a large, high roadcut (outcrop
E); pull over near sign and continue along
the shoulder to the base of the outcrop.
12.00.1Passengers disembark for Stop 1-2A;
vehicles will proceed to Rummage Road (just
to the south), turn around, and drive back
~0.3 mi uphill (north) to reload passengers
at the top of Stop 1-2B.

Stop 1-2A: Outcrop E—Large Roadcut on U.S. 31E Just North of Rummage Road, Nelson County, Kentucky

Like Stop 1-1, this tall roadcut (Fig. 10) commences with a few meters of shaly nodular limestone, typical of the “Vinlandostrophia ponderosa zone” of Butts (1915), herein tentatively assigned to the Corryville Member of the Grant Lake Formation. These shaly limestone beds are again sharply overlain by a massive coarse and partly cross-bedded grainstone tentatively assigned to the Mount Auburn Member. Note that this grainstone is about twice as thick as at Stop 1-1, just over a mile (~2 km) to the north. Also observe that the upper part of the grainstone has large-scale cross-bedding. The top of this interval shows a thin transitional interval into the overlying medium-gray shale and muddy wackestone; we interpret these beds as the basal Arnheim Formation, perhaps representing as local facies of the Sunset Member. The wrinkled strophomenid brachiopod Leptaena, diagnostic of the lower part of the Oregonia Member of the Arnheim Formation, can often be found in the overlying shaly/rubbly interval. Bryozoans, bivalves, nautiloids, and gastropods are also abundant.

Figure 10.

Stratigraphic column for outcrop E (Stop 1-2A), with base of section on the lower left. Scale in meters; abbreviations as in Figure 9.

Figure 10.

Stratigraphic column for outcrop E (Stop 1-2A), with base of section on the lower left. Scale in meters; abbreviations as in Figure 9.

Walk up the hill ~0.1 mi (~0.2 km) to the upper cut, Outcrop D.

Stop 1-2B: Outcrop D—Upper Roadcut on U.S. 31E North of the Bullitt/Spencer County Line

This cut, featuring a major exposure on the east side of U.S. 31E and one smaller on the west, provides an overview of the lower member of the Rowland formation (formerly Rowland Member of Drakes Formation; we use Rowland formation with lower case because this rank change is informal), approximately equivalent to the lower (Fort Ancient) member of the Waynesville Formation of Ohio (Fig. 11). The base of the cut, at the south end of the western outcrop, includes fossiliferous medium-gray packstone rich in small Vinlandstrophia cf. cypha and rare V. ponderosa, overlain by pale gray silty shale and calcisiltites that show small-scale hummocky cross-lamination and little “amoebiform” chert nodules. These silty beds represent the later HST of a small scale (5th-order?) cycle at the base of sequence C5A (revised).

Figure 11.

Labeled outcrop photo of the Rowland Formation at outcrop D (Stop 1-2B). Note geologists for scale.

Figure 11.

Labeled outcrop photo of the Rowland Formation at outcrop D (Stop 1-2B). Note geologists for scale.

These silt beds are sharply overlain by pale greenish, laminated dolostone and these, in turn, by a distinctively rhythmic succession of white weathering micritic wackestone and thin dark-gray soft, fissile shale beds. Note a dark shale layer full of small domal Cyphotrypa bryozoans and a thick upper 20 cm limestone ledge with scattered vuggy corals/stromatoporoids. This cyclic wackestone-shale interval has been termed the Fisherville submember from sections southeast of Louisville where the unit contains coral biostromes. It appears to represent a deepening upward (transgressive) succession; we tentatively interpret it as the TST of subsequence C5B. A pale greenish-gray shale (the Cyphotrypa shale of Butts, 1915) overlying the Fisherville at its type section is absent here, apparently removed at a cryptic unconformity at the contact with the overlying upper member of the Rowland, a package of buff-colored dolomitic mudstones that forms the upper half of the cut. In outcrops to the south, the upper Rowland first rests on the shaly and cherty siltstone beds and farther south, near Bardstown, Kentucky, on the Leptaena-bearing beds of the Arnheim Formation, which are there called the Reba Member of the Ashlock Formation.

Vehicles will reload passengers near the upper (northern) end of the roadcut, then resume the trip northward to Outcrop B to examine the upper Rowland formation.

Cum. mileageMileageDescription
13.10.8Retrace route northward to the lower
(northern) end of outcrop B, about a mile
north of Rummage Road and 0.4 mi north
of KY Rte. 48.
Cum. mileageMileageDescription
13.10.8Retrace route northward to the lower
(northern) end of outcrop B, about a mile
north of Rummage Road and 0.4 mi north
of KY Rte. 48.

Stop 1-3: Outcrop B—New Cut on U.S. 31E North of KY Rte. 48

This long outcrop exposes the entirety of the upper Rowland formation (some 10 m; Fig. 12). The gray micrites and dark shales of the upper Fisherville beds are poorly exposed in the grassy section at the north of the main roadcut. A basal blocky dolostone with dark-green glauconite or verdine(?) filled burrows is found in nearly all sections of the Rowland; it rests disconformably on the ribbon limestones of the underlying lower member of Rowland formation (Fisherville submember). This bed is interpreted as an initial transgression following a period of erosion, the mid-Richmondian unconformity (Aucoin and Brett, 2016), that marks the C5/C6 sequence boundary (revised). Most of the unit consists of blocky to massive dolomitic mudstone with thin shale partings. Fossils are sparse and dominated by the domal trepostome bryozoan Cyphotrypa. The upper Rowland is an enigmatic facies, possibly recording lagoonal to peritidal environments, that appears to pass northward first into the gastropod shoal grainstone of the Marble Hill Member (Swadley, 1979), and then into the brachiopodrich packstone and shale of the upper Waynesville Formation (Blanchester Member).

Figure 12.

Stratigraphic column for outcrop B (Stop 1-3), with base of section in the lower left. Scale in meters; abbreviations as in Figure 9.

Figure 12.

Stratigraphic column for outcrop B (Stop 1-3), with base of section in the lower left. Scale in meters; abbreviations as in Figure 9.

After inspecting the Rowland, vehicles travel south once again, past outcrops C through F, to continue stratigraphically upward.

Cum. mileageMileageDescription
14.11.0Proceed south past Rummage Road at the
south end of outcrop E.
14.20.1Cross the East Fork of Coxs Creek.
14.50.3Rather poor exposures (outcrop F) showing
possible grainstones.
14.70.2High Grove Lane on right (west); pull
off and park just beyond this junction for out
crop G.
Cum. mileageMileageDescription
14.11.0Proceed south past Rummage Road at the
south end of outcrop E.
14.20.1Cross the East Fork of Coxs Creek.
14.50.3Rather poor exposures (outcrop F) showing
possible grainstones.
14.70.2High Grove Lane on right (west); pull
off and park just beyond this junction for out
crop G.

Stop 1-4: Outcrop G—Cut in Bluff above U.S. 31E Just South of High Grove Lane, Nelson County, Kentucky

The main section is recessed from the road berm, with beds of the upper Rowland and basal Bardstown poorly exposed in the graded slope at the base. This low bluff shows the lower portion of the Bardstown formation (formally mapped in Kentucky as the Bardstown Member of the Drakes Formation; correlative to the Liberty Formation of Ohio and uppermost Dillsboro Formation of Indiana) and exposes two closely spaced coral biostromes, informally known as the “Bardstown reef.” These beds of calcareous mudstone contain large, well-preserved Tetradium, honeycomb-like heads of the colonial rugosan Cyathophylloides, the rare tabulate Calapoecia (easily recognizable with its round corallites), elongated aulacerid stromatoporoids, and others. The two biostromes are separated by calcareous silty mudstone with a layer of Tetradium. The overlying beds are poorly exposed nodular limestones that will be seen at Stop 1-7.

If time permits, continue south for optional Stop 1-5 (a more extensive exposure of the uppermost Rowland and basal Bardstown). Otherwise reverse direction and retrace route north to Stop 1-6.

Cum. mileageMileageDescription
15.30.6Proceed south; pass junction with Kentucky
Route 480 (Solitude Road).
16.41.1Pass junction with Kentucky Route 523
(Deatsville Road).
17.10.7Outcrop H, a large outcrop on both sides
of U.S. 31E in the Rowland formation; the
lower shale-rich member shows increased
amounts of white amoebiform chert
nodules—this facies persists to the south; the
Fisherville beds are still well represented
and resemble those in outcrop D.
18.11.0Outcrop I, a high roadcut on both sides
of the road; pull over.
Cum. mileageMileageDescription
15.30.6Proceed south; pass junction with Kentucky
Route 480 (Solitude Road).
16.41.1Pass junction with Kentucky Route 523
(Deatsville Road).
17.10.7Outcrop H, a large outcrop on both sides
of U.S. 31E in the Rowland formation; the
lower shale-rich member shows increased
amounts of white amoebiform chert
nodules—this facies persists to the south; the
Fisherville beds are still well represented
and resemble those in outcrop D.
18.11.0Outcrop I, a high roadcut on both sides
of the road; pull over.

Stop 1-5 (Optional): Outcrop I—U.S. 31E North of Kimmerly Road

This trench-like roadcut shows the upper half of the pale buff to gray Rowland formation overlain by thin-bedded darker-gray shales and thickly bedded muddy packstones of the lower Bardstown formation. These rhythmic beds are beneath the pair of coral-rich beds viewed at Stop 1-4. Here the coral biostromes are barely visible in the graded slope at the top of the cut, ~3 m above the base of the Bardstown. The rubbly nature of the upper benches makes for excellent collecting and small coral heads and aulacerid sponges are common.

Cum. mileageMileageDescription
18.20.1Use the junction with Kimmerly Road to
reverse direction and return north to outcrop
G (at High Grove Lane).
21.73.5Junction of High Grove Lane; note that
subsequent mileage assumes that the
optional stop was visited, otherwise subtract
7.0 mi from the total, i.e., starting at
14.7 mi instead of 21.7 mi.
26.44.7Retrace route to roadcut on the west side
of U.S. 31E near junction of S 31E Loop
(Route 877D), an outcrop of Fisherville
submember (lower Rowland) overlain
unconformably by upper member of the
Rowland formation.
Cum. mileageMileageDescription
18.20.1Use the junction with Kimmerly Road to
reverse direction and return north to outcrop
G (at High Grove Lane).
21.73.5Junction of High Grove Lane; note that
subsequent mileage assumes that the
optional stop was visited, otherwise subtract
7.0 mi from the total, i.e., starting at
14.7 mi instead of 21.7 mi.
26.44.7Retrace route to roadcut on the west side
of U.S. 31E near junction of S 31E Loop
(Route 877D), an outcrop of Fisherville
submember (lower Rowland) overlain
unconformably by upper member of the
Rowland formation.

Stop 1-6: Roadcut on West Side of U.S. 31E Just South of Junction with S 31E Loop, South of Mount Washington, Kentucky

This low outcrop shows the full succession of Fisherville submember of the lower member of Rowland formation, ~2 m of rhythmically bedded, pale weathering micritic wackestone and dark, fissile shale bands (Fig. 13). The basal 30+ cm, largely covered in talus, is considerably shalier than the overlying beds and a pale greenish color. Blocky, buff to green weathering beds are poorly exposed just below the grass line, representing the upper member of Rowland. The entire succession is interpreted to represent a shallow but relatively low-energy depositional environment, perhaps lagoonal.

Figure 13.

Outcrop photo and stratigraphic column (note: not aligned to one another) of the rhythmic micrites and organic-rich shales of the Fisherville beds of the lower Rowland formation, along U.S. 31E south of Mount Washington, Kentucky (Stop 1-6). Scale bar in meters.

Figure 13.

Outcrop photo and stratigraphic column (note: not aligned to one another) of the rhythmic micrites and organic-rich shales of the Fisherville beds of the lower Rowland formation, along U.S. 31E south of Mount Washington, Kentucky (Stop 1-6). Scale bar in meters.

Although only a few miles north of the previously visited cuts, the Fisherville is significantly more fossiliferous. This outcrop has yielded various ichnofossils, well-preserved modiolopsid bivalves, ramose bryozoans, Hebertella brachiopods, and a branching demosponge (Heterospongia?). A thicker bed near the top contains vuggy stromatoporoids and Tetradium. Additionally, some horizons are packed full of long, dark tubiferous fossils historically identified as the dendroid graptolite Inocaulis. However, they are understudied and may be dasyclad algae (S.T. LoDuca, 2002, personal commun.); additional research is pending to clarify their nature. They are particularly common within the dark, organic-rich layers, or at the contacts between the micrites and the dark shales. Uniquely, this outcrop also records three-dimensionally preserved specimens, which can be seen in cross section within some of the micrite beds.

Cum. mileageMileageDescription
29.22.8Proceed north to a ~0.5 mi long outcrop
ranging from Laurel (at the south) down
to upper Rowland (at the north); pull over
near junction with U.S. 31EX, next to an
old quarry, for best access to the lower part
of the section.
Cum. mileageMileageDescription
29.22.8Proceed north to a ~0.5 mi long outcrop
ranging from Laurel (at the south) down
to upper Rowland (at the north); pull over
near junction with U.S. 31EX, next to an
old quarry, for best access to the lower part
of the section.

Stop 1-7: Long Roadcut at Junction of U.S. 31E and U.S. 31EX (Old Route 31E) at Mount Washington, Kentucky

A low outcrop on the northeast corner of the U.S. 31E and U.S. 31EX intersection exposes the lower Bardstown coral beds (Fig. 14). As with Stop 1-4, this interval consists of calcareous mudstone and muddy packstone with large heads of the colonial rugose coral Cyathophylloides as well as Tetradium, the horn coral Grewingkia, aulacerid sponges, abundant Hebertella and other brachiopods, nautiloids, and bryozoans. The overlying pale, shaly weathering nodular beds yield abundant small colonies of Tetradium. Interestingly, certain specimens show attached small edrioasteroids, suggesting post mortem colonization prior to rapid burial.

Figure 14.

Stratigraphic column comparing the Bardstown biostromes at Stop 1-7 (A) and Stop 1-4 (B). Scale in meters. Row.—Rowland.

Figure 14.

Stratigraphic column comparing the Bardstown biostromes at Stop 1-7 (A) and Stop 1-4 (B). Scale in meters. Row.—Rowland.

The overlying beds, better exposed in the long roadcut on the southwest side of the road, belong to the richly fossiliferous packstone of the middle Bardstown formation. These facies trend upward into sparsely fossiliferous, silty, dolomitic mudstone with bivalves and bioturbation (the upper Bardstown, interpreted as the C6B FSST), which are sharply overlain by blocky buff dolomitic limestone with abundant poorly preserved bryozoans replaced by orange calcite or ankerite. The latter interval, informally named the Buckner bed, marks the base of the Whitewater Formation that forms sequence C7. It is locally overlain by a coral zone, the Madison biostrome or “Madison reef” of older reports. However, this biostrome is apparently absent at this outcrop, either truncated or missing due to paleoenvironmental conditions. In turn, the Buckner interval is sharply overlain by the upper Saluda submember of the Whitewater Formation (locally mapped as the Saluda Member of the Drakes Formation), a 7-m-thick, slightly greenish buff, brownish weathering laminated silty dolostone. This unit comprises a peritidal facies roughly analogous to the upper Rowland formation, and is largely devoid of fossils other than vertical burrows and other bioturbations. This succession will be observed to better advantage at the next stop, as well as at Stops 2-2 and 2-3.

ENCRUSTING ON A CORAL GRAVEYARD: A REWORKED CORAL BED FROM THE UPPER ORDOVICIAN (CINCINNATIAN, RICHMONDIAN) OF CENTRAL KENTUCKY

Timothy R. Paton, Rebecca L. Freeman, Benjamin F. Dattilo, and Carlton E. Brett

Availability of suitable substrate is a controlling factor for benthic marine organisms’ ability to establish in particular environments. Burrowers, deposit feeders, and sediment miners require soft substrates, whereas boring organisms such as clionid sponges and sipunculid worms and obligate encrusters such as most edrioasteroids, bryozoans, some sponges, certain brachiopods, and cnidarians require a hard surface for attachment. For this reason, substrate type can often be determined from both body fossils and traces. Hard substrates can be biotic (shells and skeletons) or abiotic (cobbles, rockgrounds, and hardgrounds).

We describe a new occurrence of edrioasteroid-encrusted tetradiid skeletons from the Bardstown formation (lower case indicates informal rank change; previously known as the Bardstown Member of the Drakes Formation; Upper Ordovician, middle Richmondian) near Mount Washington, Kentucky (Stop 1-7, Fig. 14). The Bardstown coral beds consist of mud-smothered, reworked specimens of the columnarid coral Cyathophylloides alveolata and the controversial “tabulate” Tetradium approximatum (Fig. 15). Researchers have long debated the taxonomic affinities of Tetradium, with recent workers variously suggesting that they are chaetetid-like sponges (Riding, 2004), red algae (Steele-Petrovich, 2009a, 2009b), or tabulate corals (Elias and Young, 2004). Trepostome bryozoans encrust the skeletons of both organisms, whereas stromatoporoids and isorophid edrioasteroids show a preference for encrusting T. approximatum.

Figure 15.

Bardstown coral bed fauna (1 cm scale bars): (A) fractured Tetradium approximatum skeleton displaying partial infilling of tabulae with carbonate mud; (B) two Isorophus cf. austini encrusting the top surface of a T. approximatum skeleton; (C) a stromatoporoid encrusting the skeleton of T. approximatum; and (D) three Isorophus cf. austini. The two individuals on the right are intercepted and disturbed by a burrow.

Figure 15.

Bardstown coral bed fauna (1 cm scale bars): (A) fractured Tetradium approximatum skeleton displaying partial infilling of tabulae with carbonate mud; (B) two Isorophus cf. austini encrusting the top surface of a T. approximatum skeleton; (C) a stromatoporoid encrusting the skeleton of T. approximatum; and (D) three Isorophus cf. austini. The two individuals on the right are intercepted and disturbed by a burrow.

Cincinnatian coral beds have long been referred to as reefs (e.g., Foerste, 1909; Butts, 1915; Browne, 1964), although the corals do not appear to be bound together or form mounded geometries and thus cannot be true reefs (see “Paleoecology of the Jeffersonville Limestone Coral Zone Biostrome at the Falls of the Ohio” section below for further discussion). These beds were deposited on the Lexington carbonate platform (a mixed siliciclastic-carbonate platform) in shallow, subtropical waters in an arid climate. Because of the aridity, many of these strata are dolomitized and vugs are common. The Bardstown coral beds are widely exposed in the Louisville area, for example at localities near Coxs Creek (Stops 1-4 and 1-5; Fig. 14). These other localities typically display corals that appear significantly less reworked, most appearing to be preserved in life position, and without encrusters.

Encrusting organisms typically require hard surfaces for attachment and use mineral or organic substances to cement themselves to the substrate. In muddy environments, such as that preserved in the lower Bardstown formation, encrusters usually occupy biotic hard substrates. While encrusted brachiopod valves are rare at the studied locality, up to 36% of Tetradium remains and 21% of Cyathophylloides remains host encrusters. The only taxa observed to encrust Cyathophylloides are trepostome bryozoans. Tetradium skeletons, however, host trepostomes, encrusting mamelose stromatoporoids, and isorophid edrioasteroids. Despite Cyathophylloides providing a greater total surface area for encrustation, Tetradium hosts both a greater total number and greater diversity of encrusters (Fig. 15B). The Cyathophylloides colonies are typically intact, although septae are frequently filled with carbonate mud. The Tetradium, in contrast, are variably fractured and have both mud- and spar-filled tabulae (Fig. 15A). Encrusters occupy the tops, bottoms, sides, and fractured edges of Tetradium. Modern corals possess allochemical defenses that prohibit organisms from encrusting them, and most Paleozoic corals are free of encrusters. Thus, multiple lines of evidence allow us to infer that the Bardstown corals were encrusted post mortem.

Tetradium skeletons below the upper coral bed host encrusters, which also overgrow the indurated carbonate mud that partially covers the skeleton. This indicates burial of the corals and cementation of a veneer of mud to the skeletal clast prior to being reworked, likely by storm-wave action. After reworking, these clasts behaved as hard substrate ‘islands’ for the encrusting fauna. Many of these clasts supported multiple individual edrioasteroids or bryozoan colonies. One Tetradium hosts a stromatoporoid that itself is encrusted by a bryozoan, indicating some period of residence on the sea floor before final burial. Available Cyathophylloides skeletons do not appear to have undergone significant reworking as they are unfractured and host fewer sclerobionts.

Encrusting trepostome bryozoans display two growth morphologies: sheet-like colonies and mound-like elevated colonies. These taxa are typically 1-3 cm in diameter and can reach 2 cm in height. In contrast, encrusting stromatoporoids are often large (up to 20 cm long and 15 cm tall) and cover entire sides of coral skeletons (Fig. 15C). These calcareous sponges possess mamelons but recrystallization obscures internal structures and hinders specific identification. Finally, isorophid edrioasteroids (Figs. 15B, 15D) are unusually common on Tetradium clasts and range in size from 1 to 16 mm (Fig. 16A). These edrioasteroids are characterized by four primary oral cover plates and double biserial ambulacral cover plates and are thus assigned to Isorophus Foerste, 1916. This species shares affinities with Isorophus austini Foerste, 1914, which is known from the Whitewater Formation. However, a more definite species designation will follow recovery of more complete material. Several previous reports have noted “Agelacrinites” encrusting Tetradium in the Cincinnati Arch region (Foerste, 1896; Williams, 1918). Recent work has restricted the genus Agelacrinites to the Devonian, and the two edrioasteroid occurrences share affinities with the Bardstown taxon. As such, both other occurrences are recognized here to belong to Isorophus.

Figure 16.

Bardstown coral bed encrusting fauna: (A) size frequency distribution of Isorophus cf. austini; and (B) proportion of encrusted corals and sclerobiont types.

Figure 16.

Bardstown coral bed encrusting fauna: (A) size frequency distribution of Isorophus cf. austini; and (B) proportion of encrusted corals and sclerobiont types.

The Bardstown coral beds contain variably reworked and encrusted corals that host a low diversity encrusting fauna, notably with isorophid edrioasteroids (Fig. 16). The pattern of higher species richness on Tetradium skeletons could be a function of its smaller septae and less irregular surfaces, which may have allowed edrioasteroids, with unplated basal surfaces and less flexible growth habits than bryozoans, to encrust these clasts (Fig. 16). Alternatively, the Cyathophylloides may occupy horizons that are characterized by less reworking, or were otherwise less hospitable to echinoderm growth.

Cum. mileageMileageDescription
30.81.6Proceed north to the next major outcrop
at Thixton; disembark near lower (southern)
end of cut, near a wall of massive Saluda;
vehicles will continue ~0.2 mi to the upper
end of the cut.
Cum. mileageMileageDescription
30.81.6Proceed north to the next major outcrop
at Thixton; disembark near lower (southern)
end of cut, near a wall of massive Saluda;
vehicles will continue ~0.2 mi to the upper
end of the cut.

Stop 1-8: Major Roadcut on Both Sides of U.S. 31E at Thixton, Kentucky

This long roadcut provides a magnificent, nearly continuous section from the uppermost unit of the Ordovician upward through the lower and middle Silurian (Llandovery to middle Wenlock; Fig. 17). Of the local Silurian units, only the Louisville Formation is absent here, and even that is exposed slightly north on the highway. The section begins with several meters of laminated, buff-weathering dolosiltite representing the upper part of the Saluda Member of the Whitewater Formation. As is typical, the Saluda here is unfossiliferous and apparently records aggradational tidal flat sediments deposited during an initial slow baselevel rise (the C7B TST).

Figure 17.

Stratigraphic column and carbon isotope curve for the Thixton U.S. 31E roadcut (Stop 1-8). Scale bar in meters; sequence abbreviations as in Figure 9. Brass—Brassville; Dol—Dolomite; Fm—Formation; Sh—Shale.

Figure 17.

Stratigraphic column and carbon isotope curve for the Thixton U.S. 31E roadcut (Stop 1-8). Scale bar in meters; sequence abbreviations as in Figure 9. Brass—Brassville; Dol—Dolomite; Fm—Formation; Sh—Shale.

A sharp but relatively low-relief erosional surface, the Cherokee unconformity, separates the upper Katian (upper Ka3 or Ka4) Saluda from the overlying lower Silurian formation informally termed the “golden Brassfield.” Despite its name, this yellowish weathering, medium-bedded, amalgamated grainstone-rudstone is apparently not equivalent to the Brassfield Formation of the eastern Cincinnati Arch. Rather, it is a mid-Llandovery (Aeronian?; Distomodus kentuckyensis conodont zone) unit, probably correlative to the Oldham Limestone exposed in central and eastern Kentucky, and represents a part of sequence S-II. The golden Brassfield shows numerous irregular, greenish (glauconitic?) mud-filled fractures, possibly associated with karst. Conodonts suggestive of a Telychian age have been obtained from the golden Brassfield in this area (M. Kleffner, 2017, personal commun.), raising the possibility that the golden Brassfield is a heavily condensed unit containing both Aeronian and lower Telychian strata.

The second Silurian unit, the Lee Creek Formation (formerly the Lee Creek Member of Brassfield; see Brett et al., 2012), is composed of ~1.2 m of pale orange weathering, burrow mottled argillaceous dolostone in three major beds (Fig. 17). Locally, the middle bed is separated, by ~15 cm of brick-red weathering silty dolostone, from the uppermost 30–40 cm blocky and slightly glauconitic dolostone. At most localities, the Lee Creek yields lower Telychian conodonts of the Pterospathodus eopennatus Superzone, suggesting at least partial equivalence to the Waco Formation in central and eastern Kentucky. Interestingly, however, the zonally significant conodont Pt. am. amorphognathoides was recovered from the Lee Creek at Mount Washington by Nicoll and Rexroad (1968, their table 1, locality 21). The range of Pt. am. amorphognathoides (Te4-Sh1) is considerably higher than Pt. eopennatus. This suggests the presence of a cryptic disconformity within the Lee Creek Formation. Unfortunately, Nicoll and Rexroad (1968) did not provide detailed sample measurements, so additional work is required to understand the position of the disconformity. We tentatively equate the glauconitic upper beds of the Lee Creek in this area with the glauconite-rich, Pt. amorphognathoides-bearing Dayton Formation of Ohio, of latest Telychian age. If these chronostratigraphic correlations are correct, the TSTs of both S-III and S-IV are represented in the Lee Creek Formation.

The upper bed of the Lee Creek (Dayton?) is abruptly but perhaps conformably overlain by the Osgood Formation (sensu stricto), ~5.5 m thick at this locality. The basal 2.5 m, partially covered, consists of distinctly banded maroon and green clay shales that are quite similar to the lower to middle Estill Shale (Alger Formation) in eastern Kentucky and southern Ohio. These rhythmic beds suggest possible redox cyclicity, perhaps recording precessional oscillations in climate. They are overlain by ~3 m of interbedded olive-gray dolomitic shale and thin- to medium-bedded, orange-brown silty argillaceous dolomudstone typical of the Osgood in this portion of Kentucky. Detailed study by J. Thomka (2015) demonstrates a bed-for-bed match of the distinctive carbonate shale rhythms between these and all other sections in the western Cincinnati Arch region, and possibly as far south as the Nashville Dome of Tennessee and as far northeast as Rochester, New York. The Osgood contains conodonts belonging to the Upper Pterospathodus am. amorphognathoides Zonal Group and Kockelella ranuliformis Superzone (which includes both the Lower and Upper K. ranuliformis zones), spanning latest Llandovery to earliest Wenlock (M. Kleffner, 2012, personal commun.). The δ13Ccarb data from this section show the distinctive rising limb of the early Shein-woodian (Ireviken) positive δ13Ccarb excursion (Fig. 17). The elevated δ13Ccarb values continue into the base of the overlying Lewisburg Formation.

The Osgood Formation is sharply and disconformably overlain by massive pale gray, vuggy dolostone, herein assigned to the Lewisburg Formation (formerly the “middle Osgood limestone”; Fig. 17). Conodonts suggest that at least the lower portion of this interval belongs to the K. ranuliformis Superzone and is consequently regarded as correlative with the Irondequoit Limestone, the TST of sequence S-V in the Appalachian Basin. A sharp negative shift, slightly above the initial peak, within the δ13Ccarb excursion and occurring in the middle of the Lewisburg has been recorded in all studied localities in the area and provides an excellent chronostratigraphic marker. Above this δ13Ccarb excursion, data show elevated values, suggesting that this interval is still within the peak of the Ireviken Excursion. The Massie Formation is slightly less than 1 m of dark-gray shale; it is sparsely fossiliferous but, at nearly all localities, shows small dolomicritic bioherms, some of which extend essentially through the unit. Tentatively, the Massie is regarded as the HST of S-V, but see Cramer and Kleffner in McLaughlin et al. (2008b) and Cramer (2009) for an alternate view.

The Massie is sharply overlain by beds that have been tentatively assigned as a member of the Massie. However, given that these units appear to overstep the shale to the south, we suggest that they record a distinct unit in the base of the Laurel Dolostone, separated from beds below by a discontinuity (interpreted as the S-V/S-VI sequence boundary). The remainder of the Laurel is massive to medium-bedded dolograinstone with small light-gray chert nodules. Its precise age is debated, but we tentatively correlate these beds with the upper Sheinwoodian Euphemia and Springfield Dolostone of Ohio. The upper, more tabular beds like the Springfield of Ohio locally display the same unique preservation of Gravicalymene trilobites as in the Springfield Member (Mikulic et al. inKleffner et al., 2012). The top of the massive, ~15-m-thick Laurel Formation is sharply overlain by a thin skim of “Limberlost” oolite and Waldron gray shale (S-VII).

Cum. mileageMileageDescription
34.43.6Reboard vehicles at the upper end of the
outcrop and proceed northward to the junction
with I-265; end road log for Day 1.
Cum. mileageMileageDescription
34.43.6Reboard vehicles at the upper end of the
outcrop and proceed northward to the junction
with I-265; end road log for Day 1.

Day 2: Upper Ordovician, Silurian, and Devonian Strata East and North of Louisville

Kyle R. Hartshorn, Christopher B.T. Waid, and Carlton E. Brett

The second day of the trip (Fig. 18) seeks to provide additional context to earlier localities, with several stratigraphically redundant stops to show examples of facies change within correlative strata as one heads toward the north (i.e., down paleoslope), as well as evidence for sequence-bounding regional unconformities that truncate underlying strata. Finally, a visit to the Falls of the Ohio and (hopefully) a local quarry will offer an introduction to the Middle Devonian carbonate succession of the Jeffersonville and Sellersburg formations.

Figure 18.

Regional geological map showing the Day 2 field-trip area northeast and north of Louisville, Kentucky (north of the Day 1 field-trip area shown in Fig. 7). Small black numbers are stop numbers. Abbreviations: dep.—deposits; Dol—Dolostone; Fm—Formation; Gp—Group; KGS—Kentucky Geological Survey; Ls—Limestone; opt—optional; Sh—Shale. Base map credit: ESRI.

Figure 18.

Regional geological map showing the Day 2 field-trip area northeast and north of Louisville, Kentucky (north of the Day 1 field-trip area shown in Fig. 7). Small black numbers are stop numbers. Abbreviations: dep.—deposits; Dol—Dolostone; Fm—Formation; Gp—Group; KGS—Kentucky Geological Survey; Ls—Limestone; opt—optional; Sh—Shale. Base map credit: ESRI.

Road Log

The second day’s road log starts at the hotel, off Blairwood Road on the east side of Louisville, and ends at the Falls of the Ohio State Park in Clarksville, Indiana. A subsequent quarry stop near Sellersburg, Indiana, is tentatively planned, but highly dependent on conditions and the permission of quarry owners, and thus cannot be included with certainty.

Cum. mileageMileageDescription
0.00.0Exit hotel parking lot and turn right (east)
onto Blairwood Road.
0.10.1Turn right (south) onto S. Hurstbourne
Parkway.
0.30.2Use left two lanes to merge onto
I-64 eastbound.
2.01.7Take I-64 Exit 17 for S. Blankenbaker
Parkway.
2.70.7Merge onto S. Blankenbaker Parkway and
head south (right).
4.11.4Safely make a U-turn at Rehl Road (on the
left/east).
4.30.2Pull off to the right onto incomplete roadway
with low roadcuts on the east side of
Blankenbaker Parkway (directly across
from the entrance to 2700 Blankenbaker
Parkway, currently featuring a sign for
Honeywell).
Cum. mileageMileageDescription
0.00.0Exit hotel parking lot and turn right (east)
onto Blairwood Road.
0.10.1Turn right (south) onto S. Hurstbourne
Parkway.
0.30.2Use left two lanes to merge onto
I-64 eastbound.
2.01.7Take I-64 Exit 17 for S. Blankenbaker
Parkway.
2.70.7Merge onto S. Blankenbaker Parkway and
head south (right).
4.11.4Safely make a U-turn at Rehl Road (on the
left/east).
4.30.2Pull off to the right onto incomplete roadway
with low roadcuts on the east side of
Blankenbaker Parkway (directly across
from the entrance to 2700 Blankenbaker
Parkway, currently featuring a sign for
Honeywell).

Stop 2-1: Roadcut on the East Side of Blankenbaker Parkway East at Jeffersontown, Kentucky

Small and unassuming, this low roadcut on the east side of Blankenbaker Parkway provides a rare opportunity to easily view a relatively obscure unit: the Limberlost Oolite. The basal meter or so of the outcrop exposes the uppermost Laurel Formation, with the unit’s typical massively bedded dolostone. The uppermost zone and overlying bench expose a slightly recessive, more readily weathering horizon with abundant ooids in a gray to locally rusty-red matrix. This is the Limberlost Oolite, a thin (typically less than 50 cm in this region) unit that we interpret as the shoaling and transgression of sequence S-VII. It is sparsely fossiliferous, with crinoid debris, trilobite fragments, and poorly preserved brachiopods.

Sloughed and highly weathered bluish-gray shale and sporadic siltstones at the north end of the roadcut are all that is exposed of the overlying Waldron Shale. Although richly fossiliferous in its type region near Waldron, Indiana, as well as certain localities west of Nashville, Tennessee, the Waldron of Kentucky is often barren, including at this location. Large limestone blocks, presumably Louisville Limestone, are scattered on the grassy hill upslope of the exposure.

Cum. mileageMileageDescription
0.00.0Reset mileage before continuing (for the
benefit of future users of this guide, who
may not be starting from the same hotel).
1.31.3Return north on Blankenbaker Parkway
to I-64, then turn right onto the eastbound
entrance ramp.
3.21.9Drive east on I-64 to the interchange
with I-265 and take Exit 19B for
I-265 northbound.
6.43.2Pass flooded quarry on the east (right) side
of I-265 just south of Old Henry Road with
excellent but inaccessible exposures of
Waldron Shale at the top of the highwall.
12.35.9Take I-275 Exit 35A for I-71 eastbound/
northbound toward Cincinnati.
14.62.3Cross the Jefferson/Oldham County line
into Oldham County.
16.01.4Small outcrop of Osgood Formation, showing
rhythmic banding, as well as Brassfield
and Saluda strata.
16.60.6Trench-like outcrop of Osgood, Lewisburg,
Massie, and especially Laurel formations.
17.20.6Outcrop of uppermost Osgood, Lewisburg,
Massie, and lower Laurel formations.
17.40.2High walls of upper Laurel Formation
capped by residual Waldron Shale at
the Exit 14 offramp for Kentucky
Route 329.
18.20.8Low outcrops of upper Laurel; note Waldron
and Louisville on the north side.
20.62.4Outcrops of upper Laurel and Waldron at
the top of the Exit 17 interchange for Kentucky
Route 146.
21.40.8Take Exit 18 for Kentucky Route 393
(Buckner, Kentucky).
21.70.3Pull over near the end of the exit ramp,
along the associated roadcut; passengers
will get out; vehicles will proceed right
(south) on KY 393 for ~0.2 mi to just
before Briar Ridge Road.
Cum. mileageMileageDescription
0.00.0Reset mileage before continuing (for the
benefit of future users of this guide, who
may not be starting from the same hotel).
1.31.3Return north on Blankenbaker Parkway
to I-64, then turn right onto the eastbound
entrance ramp.
3.21.9Drive east on I-64 to the interchange
with I-265 and take Exit 19B for
I-265 northbound.
6.43.2Pass flooded quarry on the east (right) side
of I-265 just south of Old Henry Road with
excellent but inaccessible exposures of
Waldron Shale at the top of the highwall.
12.35.9Take I-275 Exit 35A for I-71 eastbound/
northbound toward Cincinnati.
14.62.3Cross the Jefferson/Oldham County line
into Oldham County.
16.01.4Small outcrop of Osgood Formation, showing
rhythmic banding, as well as Brassfield
and Saluda strata.
16.60.6Trench-like outcrop of Osgood, Lewisburg,
Massie, and especially Laurel formations.
17.20.6Outcrop of uppermost Osgood, Lewisburg,
Massie, and lower Laurel formations.
17.40.2High walls of upper Laurel Formation
capped by residual Waldron Shale at
the Exit 14 offramp for Kentucky
Route 329.
18.20.8Low outcrops of upper Laurel; note Waldron
and Louisville on the north side.
20.62.4Outcrops of upper Laurel and Waldron at
the top of the Exit 17 interchange for Kentucky
Route 146.
21.40.8Take Exit 18 for Kentucky Route 393
(Buckner, Kentucky).
21.70.3Pull over near the end of the exit ramp,
along the associated roadcut; passengers
will get out; vehicles will proceed right
(south) on KY 393 for ~0.2 mi to just
before Briar Ridge Road.

Stop 2-2A: Roadcut on KY 393 Just South of 1-71 near Buckner, Kentucky

This relatively fresh outcrop exposes a thick section of the upper Cincinnatian (upper Katian; Richmondian) Bardstown and Whitewater formations (Fig. 19). The lower part of the cut, coincident with the eastbound off- and on-ramps to I-71, exposes the rubbly, brown-weathering limestones of the Bardstown formation (formerly the Bardstown Member of the Drakes Formation, equivalent to the Liberty Formation of Indiana and Ohio). A coarse cross-bedded grainstone occurs locally in the base of the Bardstown (Kepferle, 1977). The overlying bluish-gray limestone is equivalent to the Bardstown reef, a coral-rich biostrome that is especially well-developed south of Louisville (as seen on Day 1) and in the type area of Bardstown, Kentucky. The basal calcarenite and overlying Bardstown biostrome are interpreted as the C6B TST. The overlying section consists of interbedded wavy to nodular argillaceous packstones and gray shales, which we interpret as the C6B HST, overlying a flooding surface atop the biostrome. Both are very fossiliferous, with abundant brachiopods (Hebertella, Rafinesquina, Hiscobeccus), ramose bryozoans, and solitary rugose coral, mainly Grewingkia. Colonial corals are rarer in this interval, but occasionally present.

Figure 19.

Stratigraphic column for the Bardstown-Whitewater succession along KY 393 near Buckner, Kentucky; note that “Lower Whitewater” is equivalent to lower Saluda submember of text. The bryozoan-rich bed at 10.8-12.5 m is referred to as the Buckner submember. Scale in meters.

Figure 19.

Stratigraphic column for the Bardstown-Whitewater succession along KY 393 near Buckner, Kentucky; note that “Lower Whitewater” is equivalent to lower Saluda submember of text. The bryozoan-rich bed at 10.8-12.5 m is referred to as the Buckner submember. Scale in meters.

The upper 2.5 m of the Bardstown is a distinctive, blocky silty dolomitic mudstone, medium dark-gray on fresh surfaces but weathering to a light buff gray. This interval is sparsely fossiliferous but forms a distinctive taphofacies, with the soft substrate full of trace fossils such as Planolites and Chondrites. These burrows easily stand out, a result of their infillings being lighter colored than the surrounding matrix. Bivalves are also somewhat common. Although moldic, many preserve a black periostracal film, and some are articulated and in possible life position. Others are splayed or “butterflied,” suggesting relatively rapid rates of burial. A thin, dark-gray shale occurring near the top of this interval has yielded carbonized branching stains of possible dasyclad algae, like those seen in the Fisherville submember at Stop 1-6. We interpret this relatively abrupt shift from fossiliferous, shaly packstone to nearly barren mudstone as a late highstand to falling stage, with the latter recording a rapid base-level fall (forced regression) that triggered offshore deposition of mud and silt.

The base of the Whitewater Formation, the Buckner sub-member, is sharply set off from the underlying mudstone at an erosional contact we interpret as the C6/C7 sequence boundary (Fig. 19). The overlying shelly lag bed, a few centimeters thick, contains abundant rip-up clasts of dolomitic mudstone in a coarse matrix with abundant bryozoan fragments. Intact bryozoan colonies in possible life position appear above this basal lag. This interval is followed by ~7.5 m of blocky dolostone ranging from sparsely to highly fossiliferous. The uppermost 2 m are more compact and contain numerous lenses and stringers of white to pale orange recrystallized bryozoans: the Buckner submember, named for this locality and interpreted as the C7A TST. Small colonies of colonial corals are common near the top of this bed, about half of which are inverted; this may be an equivalent of the “Madison biostrome” better developed to the north. Silicified white specimens are particularly common at the upper contact with a distinctive dark-gray clay shale, ~10 cm thick. This thin shale is sharply overlain by a 90 cm blocky argillaceous dolostone with a few fossils (the Sligo bed, named for exposures near Sligo, Kentucky, some 20 km to the northeast) followed by a second 10-cm-thick shale zone. Intriguingly, these thin shales appear to be widely traceable as regional markers.

The upper submember of Saluda Member (or Saluda sensu stricto) consists of massive, pale orange-buff weathering, evenly laminated dolostone; vertical burrows, symmetrical ripples, and possible desiccation cracks are observable in cross section. We interpret its base as an erosion surface. Initial transgression brought conditions locally to peritidal environments, followed by an interval, perhaps representing little time, of approximate equilibrium between sedimentation, sea level, and subsidence during stillstand to slightly rising sea level (the C7B early TST). During this time, mixed siliciclastic and carbonate mud and silt were deposited rapidly in tidally influenced mudflats over much of the region.

Younger strata, represented by the Hitz or upper Whitewater beds, are absent at this locality and nearby where they have been removed by the Cherokee unconformity. However, this truncation is not uniform across the region, and the Hitz Member is still locally present at least as far south as Jeffersontown, Kentucky (e.g., along I-64 just east of I-265).

Cum. mileageMileageDescription
22.71.0Turn around at Briar Ridge Road and
return north; if time allows, continue north
past the highway junctions and under I-71
and up the hill to a small quarry or borrow
pit on the right (east) side of KY 393
(Stop 2-2B); otherwise take I-71
westbound onramp.
Cum. mileageMileageDescription
22.71.0Turn around at Briar Ridge Road and
return north; if time allows, continue north
past the highway junctions and under I-71
and up the hill to a small quarry or borrow
pit on the right (east) side of KY 393
(Stop 2-2B); otherwise take I-71
westbound onramp.

Stop 2-2B (Optional): Small Quarry East of KY 393 North of 1-71 near Buckner, Kentucky

This small man-made exposure just east of KY 393 provides quick and easy access to the uppermost Osgood, Lewisburg, Massie, and basal Laurel formations (Fig. 20). These beds overlie the top of the succession at Stop 2-2A, lacking only the golden Brassield, Lee Creek, and basal beds of the Osgood Formation, seen next at Stop 2-3. The upper, rhythmically bedded Osgood is exposed low in this section, sharply overlain by the ~3-m-thick Lewisburg, comprised of orange-weathered, crinoidal dolostone with occasional moldic atrypids and other brachiopods. About 90 cm of the dark-gray shaly Massie Formation follow. The centerpiece of this outcrop is a 2-3-m-wide bioherm in the Massie (Fig. 18). Another smaller bioherm occurs near the west side of the main north wall of the quarry. Note that the beds of the overlying Laurel form a gentle anticline as they are compactionally draped over the resistant micritic bioherm.

Figure 20.

View of the small roadside exposure along KY 393 north of I-71 near Buckner, Kentucky, showing a large bioherm in the ~90-cm-thick Massie Formation, draped by deformed basal Laurel Formation dolostone above.

Figure 20.

View of the small roadside exposure along KY 393 north of I-71 near Buckner, Kentucky, showing a large bioherm in the ~90-cm-thick Massie Formation, draped by deformed basal Laurel Formation dolostone above.

Cum. mileageMileageDescription
23.10.4Return south, then turn right (west) toward
the I-71 westbound entrance ramp.
24.00.9Roadcut exposing the Osgood, Lewisburg,
Massie, and Laurel formations.
24.20.2Exposures of tabular uppermost Laurel and
Waldron near Exit 17.
26.72.5Outcrop on the right (north) side of
the interstate descending through the
Louisville, Waldron, and upper
Laurel formations.
26.90.2Take Exit 14 for Crestwood and KY 329,
noting exposures of Osgood, Lewisburg,
Massie, and Laurel along the offramp and
adjacent KY 329.
27.10.2Turn left (south) onto KY 329, passing
under I-71.
27.40.3Find parking at a cluster of gas stations
and other small establishments or at a local
park-and-ride lot just to the south, then
proceed on foot to the conspicuous outcrop on
the east side of KY 329.
Cum. mileageMileageDescription
23.10.4Return south, then turn right (west) toward
the I-71 westbound entrance ramp.
24.00.9Roadcut exposing the Osgood, Lewisburg,
Massie, and Laurel formations.
24.20.2Exposures of tabular uppermost Laurel and
Waldron near Exit 17.
26.72.5Outcrop on the right (north) side of
the interstate descending through the
Louisville, Waldron, and upper
Laurel formations.
26.90.2Take Exit 14 for Crestwood and KY 329,
noting exposures of Osgood, Lewisburg,
Massie, and Laurel along the offramp and
adjacent KY 329.
27.10.2Turn left (south) onto KY 329, passing
under I-71.
27.40.3Find parking at a cluster of gas stations
and other small establishments or at a local
park-and-ride lot just to the south, then
proceed on foot to the conspicuous outcrop on
the east side of KY 329.

Stop 2-3: Roadcuts along KY 329 near Crestwood/Park Lake, Kentucky

Starting on the east side of KY 329 just south of its intersection with I-71, this series of roadcuts exposes almost the entire breadth of Silurian strata present on the western flank of the Cincinnati Arch. The base of the section starts in the Upper Ordovician (upper Richmondian; upper Katian) with several meters of laminated, buff-weathering dolostone belonging to the Saluda Member of the Whitewater Formation. The upper contact of the Saluda is a major erosion surface that forms the Silurian/Ordovician boundary: the Cherokee unconformity, studied here in detail by Brett et al. (2014). Low pockets on the surface are overlain by a 0.25-1.25-m-thick yellowish-brown weathering grainstone-rudstone, the mid-Llandovery golden Brassfield Formation (Aeronian?; D. kentuckyensis conodont zone; see Brett et al., 2014, for details). The contact is highly irregular and shows grainstone-filled borings that penetrate the underlying silty dolomudstone (Fig. 21).

Figure 21.

The karstified Cherokee unconformity at Crestwood, Kentucky, showing golden Brassfield in lateral relationship with the Saluda Member, and both erosionally truncated by the Lee Creek Formation. Note hammer for scale.

Figure 21.

The karstified Cherokee unconformity at Crestwood, Kentucky, showing golden Brassfield in lateral relationship with the Saluda Member, and both erosionally truncated by the Lee Creek Formation. Note hammer for scale.

The second Silurian unit, the Lee Creek Formation, is composed of ~0.6 m of orange weathering, greenish-tan, burrowed dolomudstone. This unit contains abundant glauconite and lacks macrofossils. Nicoll and Rexroad (1968) observed reworked Ordovician conodonts within the Lee Creek Formation in nearby sections, as well as evidence for a significant biostratigraphic gap between the golden Brassfield and Lee Creek. They found that the Lee Creek conodont assemblages had the greatest similarity with those of the Merritton Limestone (S-III) of western New York. The conodonts were assigned to the Pterospathodus Zone in pre-1997 terminology; present evidence suggests an assignment to the Pt. eopennatus Superzone and hence late Llandovery (early Telychian) age, in agreement with an S-III interpretation (McLaughlin et al., 2008b). This further supports correlation with the Waco Formation of east-central Kentucky and nearby regions of Ohio. However, it is unclear whether a thin, possibly Dayton-equivalent package, with Pt. am. amorphognathoides Zone conodonts, exists at the top of the Lee Creek here as it does at Thixton (Nicoll and Rexroad, 1968).

The Osgood Formation here is composed of ~5.5 m of greenish-gray shale and thin- to medium-bedded yellowish-brown silty argillaceous dolomudstone. Shelly fossils are rare, though burrows are common. The prominent red and green banding of the basal Osgood present at Mount Washington and Thixton is not apparent here. However, the upper Osgood is more consistent across long distances (Thomka, 2015), with rhythmic intercalations of shale and dolosiltite. The uppermost package contains a particularly distinctive set of resistant beds. These are the “Crestwood beds,” named for typical exposures in this immediate vicinity (Thomka, 2015). The δ13Ccarb data from this section (Fig. 22) show the distinctive rising limb of the early Sheinwoodian (Ireviken) positive excursion and can be readily correlated with the data from Thixton (Fig. 17). Meanwhile, δ13Ccarb values appear to generally decline through the Lewisburg and Massie formations, with a slight positive deflection in the upper Lewisburg and basal Massie.

Figure 22.

Stratigraphic column and δ13Ccarb data for the Crestwood (Park Lake) composite section. The lower positive excursion, coincident with the Osgood Formation, is the Ireviken Excursion; the upper positive excursion, coincident with the Waldron Shale, is the Mulde Excursion. VPDB—Vienna Pee Dee Belemnite. Scale in meters.

Figure 22.

Stratigraphic column and δ13Ccarb data for the Crestwood (Park Lake) composite section. The lower positive excursion, coincident with the Osgood Formation, is the Ireviken Excursion; the upper positive excursion, coincident with the Waldron Shale, is the Mulde Excursion. VPDB—Vienna Pee Dee Belemnite. Scale in meters.

The latter two units and the base of the overlying Laurel Formation are well exposed at the intersection of KY 329 with the Veterans Memorial Parkway. The Lewisburg is massive dolograinstone that shows molds of crinoid ossicles. An apparently minor parting within the unit is argued by Cramer (in McLaughlin et al., 2008b) to be a major disconformity at which early Sheinwoodian strata are removed. Although we recognize that unconformities can be deceptively cryptic, available evidence does not support such a major gap at this position. We note that the upper Osgood, Lewisburg, and Massie formations show close faunal similarities, including taxa only found in these units, making a significant disruption of their depositional history unlikely.

Continuing southeast around the bend in the road, the Laurel Formation (~15 m thick) exhibits a typical vuggy lower unit and more regularly bedded dolostone. The Waldron Shale is exposed at the top of the hill, apparently in its unfossiliferous phase. However, the weathered and grassy hill slope above reveals a reddish residual soil with abundant corals, perhaps sourced from now-eroded Louisville Limestone.

Cum. mileageMileageDescription
27.80.4Return north to I-71 and turn left (west)
onto the westbound onramp to return
to Louisville.
28.10.3Roadcut through the upper Laurel.
28.60.5An exceptional outcrop of Osgood (especially
note rhythmic bedding and the resistant
Crestwood beds near the top) capped
by Lewisburg, Massie, and Laurel strata.
29.10.5Another outcrop of Osgood, Lewisburg,
Massie, and lower Laurel just before the
exit ramp to a rest area.
29.30.2Low outcrops of Laurel along I-71 adjacent
to a rest area.
29.50.2Another good exposure of upper Osgood,
Lewisburg, Massie, and lower Laurel after
the rest area.
29.90.4Beginning of a long roadcut ascending
a hill, exposing the entire upper Osgood
Formation through lower Louisville
succession; excellent exposure of Waldron
Shale sharply overlain by Louisville.
30.91.0Pass the Oldham/Jefferson County line,
reentering Jefferson County.
35.14.2Many low outcrops of Louisville Lime
stone along this stretch of highway, includ
ing small bioherms.
37.32.2Put hazard lights on while coming around
a rightward curve in I-71, pull over to the
shoulder, and prepare to safely stop at one
of a series of vertical cuts on the northeast
side of the highway.
Cum. mileageMileageDescription
27.80.4Return north to I-71 and turn left (west)
onto the westbound onramp to return
to Louisville.
28.10.3Roadcut through the upper Laurel.
28.60.5An exceptional outcrop of Osgood (especially
note rhythmic bedding and the resistant
Crestwood beds near the top) capped
by Lewisburg, Massie, and Laurel strata.
29.10.5Another outcrop of Osgood, Lewisburg,
Massie, and lower Laurel just before the
exit ramp to a rest area.
29.30.2Low outcrops of Laurel along I-71 adjacent
to a rest area.
29.50.2Another good exposure of upper Osgood,
Lewisburg, Massie, and lower Laurel after
the rest area.
29.90.4Beginning of a long roadcut ascending
a hill, exposing the entire upper Osgood
Formation through lower Louisville
succession; excellent exposure of Waldron
Shale sharply overlain by Louisville.
30.91.0Pass the Oldham/Jefferson County line,
reentering Jefferson County.
35.14.2Many low outcrops of Louisville Lime
stone along this stretch of highway, includ
ing small bioherms.
37.32.2Put hazard lights on while coming around
a rightward curve in I-71, pull over to the
shoulder, and prepare to safely stop at one
of a series of vertical cuts on the northeast
side of the highway.

Stop 2-4: The Louisville Paraconformity along I-71 East of Louisville, Kentucky

These tall, vertical interstate cuts show the cement-gray Silurian Louisville Formation overlain by the pinkish-gray, crinoid and coral-rich Middle Devonian Jeffersonville Limestone. Their inconspicuous contact is the famed Louisville (Wallbridge) paraconformity, here representing a hiatus of over 30 million years. Beds below the disconformity are dolomitic packstones with abundant small favositid and especially halysitid tabulate corals. The latter group went extinct essentially at the Silurian-Devonian boundary; hence the persistence of these corals up to the disconformity and their absence above provide a local means of identifying its position. Without such aids, the contact looks deceptively like an ordinary parting, often less distinct than other partings within the Louisville.

Above the unconformity, the Jeffersonville contains a diverse assemblage of corals, especially large heads of Favosites up to a meter across; some of these colonies are overturned. Large solitary and colonial rugose corals are also abundant. These beds represent the late Emsian–earliest Eifelian Coral Zone, which are seen to good advantage at the Falls of the Ohio.

Cum. mileageMileageDescription
38.00.7Impressive man-made “gorge” exposing
the Louisville and Jeffersonville.
42.04.0Follow signs for I-65 northbound toward
Indianapolis.
43.01.0Cross the Abraham Lincoln Bridge over the
Ohio River (note: toll bridge as of 2018);
stay in the right lane.
43.60.6Enter Indiana and take the first exit
(Exit 0 for W. Court Avenue).
43.80.2Turn left (west) onto W. Court Avenue.
44.00.2Turn left (south) onto Missouri Avenue.
44.20.2Turn right (west) onto W. Market Street.
44.30.1Merge onto E. Riverside Drive,
heading west.
45.00.7Turn left at the entrance to the Falls of the
Ohio State Park Interpretive Center; note
geologically themed architecture.
45.10.1Park in the Falls of the Ohio Interpretive
Center parking lot and disembark.
Cum. mileageMileageDescription
38.00.7Impressive man-made “gorge” exposing
the Louisville and Jeffersonville.
42.04.0Follow signs for I-65 northbound toward
Indianapolis.
43.01.0Cross the Abraham Lincoln Bridge over the
Ohio River (note: toll bridge as of 2018);
stay in the right lane.
43.60.6Enter Indiana and take the first exit
(Exit 0 for W. Court Avenue).
43.80.2Turn left (west) onto W. Court Avenue.
44.00.2Turn left (south) onto Missouri Avenue.
44.20.2Turn right (west) onto W. Market Street.
44.30.1Merge onto E. Riverside Drive,
heading west.
45.00.7Turn left at the entrance to the Falls of the
Ohio State Park Interpretive Center; note
geologically themed architecture.
45.10.1Park in the Falls of the Ohio Interpretive
Center parking lot and disembark.

Stop 2-5: Falls of the Ohio State Park, Clarksville, Indiana

The Falls of the Ohio State Park and its recently renovated interpretive center afford an overview of the Early to Middle Devonian Jeffersonville Limestone (Fig. 23). A local anticlinal structure brings these resistant strata up to the level of the Ohio River, where the bedrock then formed great rapids that hindered river travel and led to the settlement of the surrounding region. The strata exposed here are among the most fossil-rich Paleozoic sections in the world, and one of the most classic regions for the study of midcontinent Paleozoic rocks (Fig. 23). The coral beds of the Early to Middle Devonian Jeffersonville Limestone are one of the most diverse coral assemblages in the entire geologic record, with hundreds of named species (Stumm, 1964).

Figure 23.

Stratigraphic column of the Jeffersonville Limestone at the Falls of the Ohio State Park, divided into five distinct biozones (figure modified from Perkins, 1963).

Figure 23.

Stratigraphic column of the Jeffersonville Limestone at the Falls of the Ohio State Park, divided into five distinct biozones (figure modified from Perkins, 1963).

These lowest beds are only exposed when the level of the Ohio River is exceptionally low—usually in the summer and probably not during this autumn field trip. These include a few restricted areas that expose the Louisville paraconformity and underlying Silurian Louisville Formation, again with telltale halysitid corals. These are overlain by the ledges of the Coral Zone (basal Jeffersonville) only exposed at low water. Ledges above the typical river level show the smaller corals and stromatoporoids of the Amphipora ramosa Zone, named for small pipe-like colonies characteristic of the interval. Higher ledges are packed with valves of the small spiriferid brachiopod Brevispirifer gregarius, often silicified and weathering in relief on the limestone surface. Just above a persistent chert layer, the fossiliferous beds of the Bryozoan-Brachiopod Zone and the Paraspirifer acuminatus Zone yield abundant large gastropods, small rugose corals, various brachiopods, and crinoid and blastoid thecae. The overlying Sellersburg Formation (mapped as the North Vernon Formation here in Indiana) is not exposed at this locality, though fragments of this unit may sometimes be found in the cobbles along the river bank.

If water levels allow, we will examine these fossiliferous beds in person and discuss their paleoecology. Note that fossil collecting is prohibited in the park. We will also visit the nearby interpretive center, with recently redesigned exhibits that feature both the natural and human history of the Falls and the surrounding area. Also note that, unless we can arrange a brief visit to a quarry (tentative Stop 2-6—readers visiting this stop on their own must obtain permission to visit this stop), this will be the last stop of the trip and will be followed by a return to I-65 and the drive north to Indianapolis.

PALEOECOLOGY OF THE JEFFERSONVILLE LIMESTONE CORAL ZONE BIOSTROME AT THE FALLS OF THE OHIO: A TWENTY-FIRST-CENTURY UPDATE

Katherine V. Bulinski

Overview

The presence of coral-dominated ecosystems, such as reefs, can often reveal much about environmental parameters, including nutrient levels, water depth, trophic structures, and hydrodynamics. The environmental conditions of Paleozoic biostromes, made up primarily of stromatoporoids with rugose and tabulate corals, can be more difficult to decipher, as they are a distinctly different ecosystem when compared to Mesozoic and Cenozoic reefal counterparts. Biostromes, while sometimes called reefs, are actually non-framework horizons composed of densely packed coral and sponges, and do not squarely fit into the classical definition of a true reef (Cumings, 1932; Kershaw, 1994). Additionally, fundamental aspects of the biology of tabulate and rugose corals and stromatoporoids are still not fully understood, which makes interpretation of ancient biostromes and their paleoenvironments more challenging.

The Falls of the Ohio State Park in Clarksville, Indiana, is an important fossil locality, best known for its extensive exposure of a Middle Devonian biostrome with high levels of coral diversity. Even though coral fossils from this well-exposed location can be found in museums around the world, there has been only one peer-reviewed study of the paleoecology of the biostrome (Kissling and Lineback, 1967). In 2017, a new research effort began to reexamine the paleoecology of this important location. Fossil abundance, size, and orientation data were used to address three research goals: (1) to reevaluate the findings of the 1967 Kissling and Lineback study, (2) to examine and document the relationships between organisms in the Coral Zone, and (3) to examine and document evidence for paleoenvironmental parameters. The information presented herein details some of the initial results of this ongoing project.

Background

The Paleoecology of Devonian Biostromes

Throughout much of the Phanerozoic, coral-rich assemblages were important ecosystems, known to influence the bio-geochemical cycling of nutrients and create complex physical and ecological structures in shallow marine environments. The term “reef” has been used broadly to describe these ecosystems, but there are many wide-ranging terms and definitions for reefs in the biological and geological literature (e.g., bioherm, biostrome, buildup, coral thicket, stratigraphic reef, and microbial mound, among others), which can sometimes lead to confusion about the nature of environments that support coral organisms. For the purposes of this research, the broad definition of a reef proposed by Wood (1999, p. 5) is useful for anchoring the discussion of coral-rich assemblages through time: “A reef is a discrete carbonate structure formed by in-situ or bound organic components that develops topographic relief upon the sea floor.” In this definition, the words “structure” and “relief” are particularly useful for understanding precisely how reefs relate to the geological term “biostrome.” In contrast, biostromes can be defined as a bedding plane of densely packed skeletal elements that do not necessarily have an internal framework or have relief off the sea floor (Cumings, 1932; Kershaw, 1994). Without the requirement of structure or relief, biostrome horizons would not be reefs sensu stricto, but rather reflect a distinctly different kind of coral-rich ecosystem that may not have an exact modern analogue.

There are several other notable distinctions that can be made between the environmental conditions that support mid-Paleozoic biostromes and modern reefs. These include differences in water circulation patterns (i.e., epicontinental versus open ocean), and differences in ocean chemistry (i.e., aragonitic versus calcite oceans; or the influence of newly developing terrestrial ecosystems on marine environments). Additionally, the amount and types of ecological interactions between organisms are different in Paleozoic ecosystems. While many complex interactions like symbiosis and predation are well documented in Paleozoic biostrome assemblages (Segars and Liddell, 1988; Kershaw, 1998; Tapanila, 2005; Vinn and Motus, 2014), these communities pre-date the Mesozoic Marine Revolution, which played a large role in developing the complexity of behavior exhibited in modern reefs. Specifically, bioerosion is very low in Paleozoic assemblages (Kiessling, 2001) and this has an impact not only in the interaction between organisms, but also in the rate that the physical reef-like structure grew and bound loose sediment.

Additionally, ancient coral ecosystems do not have the same biological constituents of their modern counterparts. Middle Paleozoic biostromes are largely composed of extinct organisms, namely rugose and tabulate corals as well as stromatoporoid sponges. These organisms were incredibly abundant during the Middle Devonian, and by some accounts were responsible for a Phanerozoic global maximum of reef-like assemblages in the Frasnian (Kiessling, 2001). Despite their abundance and importance in Paleozoic ecosystems, there are still major unresolved questions about the biology and habitat preferences of Paleozoic corals and stromatoporoids.

Rugose and Tabulate Corals

Rugose and tabulate corals are known from the Ordovician through Permian. They are major constituents of the reef or reef-like assemblages that achieve a Phanerozoic peak during the Devonian (Kiessling, 2001). Tabulate corals are exclusively colonial, producing forms that include branches, chains, mounds, and sheet-like growth forms (Oliver and Coates, 1987). Their sizes can range from a few millimeter-sized corallites, to colonies of up to several meters across. Rugose corals exhibit both colonial and solitary forms, with solitary individuals commonly growing to sizes of several centimeters, with exceptional specimens as long as a meter. Colonial rugose corals, like the tabulate corals, can also grow to several meters across (Oliver and Coates, 1987).

The large potential size of tabulate and rugose corals begs the question as to how these organisms were able to secrete such large amounts of calcite in their skeletal structures. Modern reef-building scleractinian corals typically contain symbiotic zooxanthellae, which allow the polyps to obtain food in warm, lower-nutrient environments while also secreting large amounts of carbonate (Wood, 1999). Evidence for photosymbiosis in scleractinian corals can be traced back as far as the Middle Triassic, where annual growth bands have been documented (Stanley and Helmle, 2010). The mechanism behind large quantities of carbonate production in Paleozoic corals is not as well understood. While evidence for photosymbiosis (based on carbon and oxygen isotopic signatures) has been documented in tabulate corals dating back as far as the middle Silurian (Zapalski, 2014), photosymbiosis has not yet been documented in rugose corals, although seasonal growth banding has been observed (Berkowski and Belka, 2008). High-nutrient levels have been proposed as a possible influence on the rapid production of carbonate in these ancient reef-like assemblages (Kiessling, 2001). Coral-rich assemblages in the Middle Devonian had a wider paleolatitudinal range than that of modern true reefs, which indicates that ancient corals may have occurred in cooler-water, more nutrient-rich environments (Kiessling, 2001). Elevated levels of available nutrients may have supplied the coral with the ability to secrete large quantities of carbonate (Corlett and Jones, 2011).

Stromatoporoids

Devonian biostromes very commonly contain a record of the associations between corals and stromatoporoids. These heavily calcified Paleozoic sponges occur in multiple growth forms, including layered structures, branched coenostea, and mounds (Kershaw, 2013). While reported in the literature from the Mesozoic and Cenozoic, these occurrences are likely polyphyletic when grouped with those occurring from the Ordovician through end-Devonian (Stock, 2001). Intergrowth of corals and stromatoporoids is documented in many Silurian and Devonian ecosystems (Vinn and Motus, 2014; Vinn et al., 2015; Vinn, 2016). Rugose corals within stromatoporoids benefitted from achieving higher tiering off the sea floor for feeding, and the stromatoporoids may have benefitted structurally from the presence of the intergrown rugose corals (Vinn, 2016). Some tabulate corals, like syringoporids, are also documented as symbionts within stromatoporoids with the organisms benefiting structurally from the association (Vinn, 2016). At the same time, endobiotic corals may have negatively impacted the flow of water through the stromatoporoid, thereby reducing the effectiveness of feeding through filtration (Vinn and Motus, 2014).

Geological and Paleoecological Setting of the Falls of the Ohio

The Falls of the Ohio State Park (Clarksville, Indiana) contains the type section of the Devonian Jeffersonville Limestone (Emsian–Eifelian; Kindle, 1899), which can be delineated into five distinct biozones, differentiated by their faunal constituents and lithological qualities (Figs. 23, Fig. 24; Perkins, 1963). This ongoing work is focusing on the lowest biozone, known as the Coral Zone. This horizon extends laterally in two major areas of extensive bedding planes, often referred to as the north and south flats (Fig. 25). These are submerged under the Ohio River most of the year. During August through October, the Army Corps of Engineers lowers the water level in this part of the river channel, temporarily exposing the Coral Zone for study.

Figure 24.

Relative fossil abundance and distribution through the five biozones at the Falls of the Ohio State Park (from Greb et al., 1993; after Perkins, 1963).

Figure 24.

Relative fossil abundance and distribution through the five biozones at the Falls of the Ohio State Park (from Greb et al., 1993; after Perkins, 1963).

Figure 25.

Map of the fossil beds at the Falls of the Ohio State Park made when the water levels of this portion of the Ohio River were low. The star on the map indicates the area of the current study, while the triangle indicates the area chosen for study by Kissling and Lineback (after Greb et al., 1993; used with permission). P—parking; VC—visitors center.

Figure 25.

Map of the fossil beds at the Falls of the Ohio State Park made when the water levels of this portion of the Ohio River were low. The star on the map indicates the area of the current study, while the triangle indicates the area chosen for study by Kissling and Lineback (after Greb et al., 1993; used with permission). P—parking; VC—visitors center.

The diversity of the fauna at the Falls of the Ohio is remarkable. By some accounts, more than 600 different species of fossils have been documented across the five biozones, many of which are type specimens known only from this location (Greb et al., 1993; Powell, 1999). The Coral Zone is a true biostrome because the horizon is composed of a layer of primarily rugose and tabulate corals and stromatoporoids with little evidence of framework building. However, some stromatoporoids and colonial mounded corals are very large, in some cases up to 4 m in diameter (Greb et al., 1993). These large specimens are preserved in situ and because of their sheer size, they undoubtedly created relief off the sea floor, which departs from the classical definition of a biostrome. As a result, this assemblage may have had a patch reef-like quality, creating some habitat differentiation across the bedding plane.

Previous Study: Kissling and Lineback (1967)

The Falls of the Ohio has been a location of geologic and paleontological interest since at least 1820 when Rafinesque and Clifford published a monograph of the fossils found in the region. Since that time, there have been many studies of the fossils and geology, most notably an extensive monograph of systematic paleontology by Stumm (1964); however, the only peer-reviewed paleoecological study was conducted in 1967 by Kissling and Lineback. In their work, they performed quadrat mapping of a portion of the upper Coral Zone (see Fig. 25), where they identified and measured more than 14,000 specimens, larger than 4 cm, according to their position on the fossil beds and, when applicable, their compass orientation.

The results of their sampling revealed that 70.8% of the unbroken organisms measured were tabulate corals, 25.5% were stromatoporoids, and the remaining 3.7% were colonial rugose corals (Kissling and Lineback, 1967). They noted additional faunal constituents including branching tabulate corals and solitary rugose corals, along with minor faunal elements primarily in the lower part of the Coral Zone, such as echinoderm ossicles, the trilobite Anchiopella anchiops, and brachiopods. Perkins (1963; see Fig. 24 herein) also noted bryozoans and ostracodes in the lower Coral Zone. The colonial corals and stromatoporoids were densely packed within the bed, with a minimum of 27 and maximum of 140 coral colonies, and sponges greater than 4 cm in size documented within 10 ft × 10 ft quadrats across the Coral Zone (Kissling and Lineback, 1967).

Kissling and Lineback inferred that most large colonial corals and stromatoporoids were in life position, with a few fossils lying on their sides or entirely overturned, and reported that only 0.4% of non-branching specimens were displaced. The more delicate organisms, such as the branching corals, were fragmented, and the authors interpreted their location on the coral bed to be “near their centers of growth.” As an extension of this interpretation, they asserted that the Coral Zone represents “contemporaneous population structure and distribution of stony colonial coelenterates at one moment of geologic history” (Kissling and Lineback, 1967, p. 158).

While life position was interpreted for these larger organisms, an east/west orientation was noted for elongate fragments with a mean azimuth along the 98 (278) degree axis. Kissling and Lineback presented several hypotheses for this orientation, including orientation perpendicular or parallel to paleocurrent, positioning by oscillatory wave energy, or orientation by bidirectional water motion, suggesting a tidal effect. Of these possibilities, they favored the interpretation of an east-west tidal current, based on the orientation of the fossils, the assumption of an ancient shoreline to the east, as well as the thinning of the Coral Zone of the Jeffersonville Limestone to the east. They also noted that certain coral taxa occurred in highest abundance in a linear pattern across the bedding plane according to this proposed tidal current (Kissling and Lineback, 1967).

Kissling and Lineback presented additional paleoenviron-mental interpretations. While they suggested that the sea floor was nearly flat with a slight slope toward deeper water to the west/southwest, this could not be ascertained based on faunal composition alone, as none of the organisms were especially useful for determining water depth. They interpreted the Coral Zone to be below fair-weather wave base since the larger colonies were only rarely displaced from life position. Based on the sizes of some large branching favositid corals, they estimated that water depth could be no shallower than 6 ft, though it could certainly be deeper. The sediment present in the biostrome is largely micritic mud, with very little evidence of terrigenous input and the potential for only moderate amounts of turbidity during storm events (Kissling and Lineback, 1967).

Current Research

Because it has been more than 50 years since the Kissling and Lineback study, the current effort revisits and expands upon their research. In this work, author Bulinski and her students performed transect measurements of a portion of the upper Coral Zone to determine the distribution and orientation of fossils across the bedding plane. The current effort included all fossils greater than 1 cm in size (in contrast to the 4 cm threshold of the Kissling and Lineback study). This smaller minimum size captured most branching tabulate corals and solitary rugose coral specimens, as well as the larger colonial corals and stromatoporoids that were the focus of the Kissling and Lineback work. Given that solitary rugose corals comprise most of the fossil abundance within the Coral Zone, this is a significant faunal element that had not been examined quantitatively before.

Methodology

Fieldwork was conducted during August through October 2017, when the Ohio River was low enough to continuously expose the Coral Zone of the Jeffersonville Limestone. As the Coral Zone is exposed over hundreds of square meters, it was necessary to choose a portion of the coral beds to examine in detail. For this study, the location was selected based on the following criteria: (a) the area selected represented a single horizon (i.e., did not slope down-section because of modern river erosion), (b) the area was not greatly obscured by pooling spring-fed water, and (c) the area was easily accessible from the river bank (i.e., did not require watercraft to access). The area chosen was a portion of the north flats of the Coral Zone, easily accessible from the Falls of the Ohio State Park Interpretive Center (Fig. 25). The site chosen, while on the same “flat” of the Coral Zone as the Kissling and Lineback study, was not in exactly the same location. Even if the current research was performed in the same location as the Kissling and Lineback study, the fossils examined would still be different because of the effects of river erosion on the fossil beds over the past 50 years.

Sampling Schema

The bedding plane is so densely packed with fossils that it was difficult to conduct systematic identifications and measurements without an organized sampling strategy. Transect sampling permitted the systematic identification and measurement of every single exposed specimen along portions of the bedding plane without bias. Measuring tapes were stretched across designated areas of the bedding plane (Fig. 26), and every fossil greater than 1 cm that touched the labeled edge of the measuring tape was identified and measured. If quadrat sampling had been utilized, it is likely that the larger specimens would have been preferentially identified and measured and smaller specimens would have been overlooked. In all, 2351 fossils, all greater than 1 cm in size, across 81 m of exposed bedding were identified, measured, and, if elongate in shape, their azimuth was recorded.

Figure 26.

Sampling schematic for transects in the present study. All transects, except for D, were oriented at 325 degrees. Transect D was perpendicular, oriented at an azimuth of 235 degrees. The orientation of transects was dictated partially by spring-fed pools on the fossil beds, which made data collection difficult in the area between transects C and E.

Figure 26.

Sampling schematic for transects in the present study. All transects, except for D, were oriented at 325 degrees. Transect D was perpendicular, oriented at an azimuth of 235 degrees. The orientation of transects was dictated partially by spring-fed pools on the fossil beds, which made data collection difficult in the area between transects C and E.

Fossils were identified to the genus level where possible. Paleozoic corals are notoriously difficult to identify without thin-sectioning (Webb, 1996), particularly in a location like the Falls of the Ohio where the fossils are embedded in limestone and cannot be removed. Additionally, the corals at the Falls of the Ohio have a long history of redundant nomenclature, but much of the synonymy was resolved by Stumm (1964). Still, many fossils at the Falls of the Ohio need reevaluation and may in fact be incorrectly named. The taxonomy used in the present report are primarily genera documented by Stumm (1964); however, the genus Tabulophyllum was used here according to personal correspondence between the late William Oliver Jr. and Alan Goldstein (geologist at the Falls of the Ohio State Park). Oliver communicated that some species of the solitary rugose genus Blothrophyllum that are present in the Coral Zone may be the coral Tabulophyllum, specifically T. sinuosum and T. greeni.

Initial Results

A total of 2351 specimens were identified and measured. The areas of specimens on the bedding plane were calculated (by multiplying length and width) and used as a proxy for relative biomass for each taxon (Table 1). While using the area on the bedding plane is not an exact representation of biomass because some fossils are oriented obliquely on the surface of the Coral Zone, this measurement gives an approximation of the amount of the Coral Zone occupied by each taxon. Stromatoporoids, while making up just 5.4% of the total counted organisms along the transects, represent nearly 73% of the biomass. While some of the stromatoporoids appeared on the fossil beds as small patches, many were quite large, seven coenostea stretched more than 0.5 m across. This is a lower estimate of stromatoporoid biomass, as there were portions of the Coral Zone with a hazy appearance that may have been weathered stromatoporoids but were not considered in this study.

TABLE 1.

ABUNDANCE AND BIOMASS OF FOSSILS ALONG THE TRANSECTS

FossilAbundance (% total)Biomass (cm2) (% biomass)
Acinophyllum288 (12.3%)237.9 (0.34%)
Cladopora432 (18.4%)391 (0.57%)
Cystiphylloides254 (10.8%)2550.1 (3.7%)
Emmonsia32 (1.4%)1529.8 (2.2%)
Enalophrentis17 (0.72%)179.8 (0.26%)
Eridophyllum3 (0.13%)13.7 (0.02%)
Favosites309 (13.1%)4222 (6.1%)
Heliophyllum674 (28.7%)6867.8 (9.9%)
Pleurodictyum3 (0.13%)573.5 (0.83%)
Siphonophrentis20 (0.85%)1127.5 (1.6%)
Stromatoporoid126 (5.4%)50,311.1 (72.8%)
Tabulophyllum*193 (8.2%)1098.5 (1.6%)
Total235169,102.7
FossilAbundance (% total)Biomass (cm2) (% biomass)
Acinophyllum288 (12.3%)237.9 (0.34%)
Cladopora432 (18.4%)391 (0.57%)
Cystiphylloides254 (10.8%)2550.1 (3.7%)
Emmonsia32 (1.4%)1529.8 (2.2%)
Enalophrentis17 (0.72%)179.8 (0.26%)
Eridophyllum3 (0.13%)13.7 (0.02%)
Favosites309 (13.1%)4222 (6.1%)
Heliophyllum674 (28.7%)6867.8 (9.9%)
Pleurodictyum3 (0.13%)573.5 (0.83%)
Siphonophrentis20 (0.85%)1127.5 (1.6%)
Stromatoporoid126 (5.4%)50,311.1 (72.8%)
Tabulophyllum*193 (8.2%)1098.5 (1.6%)
Total235169,102.7
*

Note that Tabulophyllum has not yet been formally documented at the Falls of the Ohio.

Orientation data were recorded for 78% of the specimens. When considered in aggregate, there was not an obvious pattern to the orientation of the specimens (Fig. 27). When fossil orientation was subdivided coarsely into 45 degree bins, there was a slightly greater number of skeletons oriented between 45 and 90 degrees (487 out of 1833), however this result was not statistically significant (X2 = 3.646, df = 3, p = 0.3). Some portions of the transects exhibited a particular orientation of fossils locally on the bedding plane, but again, no statistically significant pattern was documented.

Figure 27.

Orientations of elongate fossils across all transects, showing that slightly more fossils were oriented between 45 and 90 degrees (but this result was not statistically significant).

Figure 27.

Orientations of elongate fossils across all transects, showing that slightly more fossils were oriented between 45 and 90 degrees (but this result was not statistically significant).

Occasional paleoecological associations were noted in fossils along the transects, although these exclusively involved stromatoporoids. It was noted that solitary rugose corals were embedded vertically through stromatoporoids, and the tabulate coral Syringopora was also observed to be embedded in several instances. Aside from coral/stromatoporoid associations, no paleoecological associations were observed, even though detailed centimeter-scale documentation of specimens was performed throughout the study area. There was also no evidence of bioerosion, drilling, boring, or encrustation. While it is possible that erosion by the river may have erased some of these traces, the high abundance and otherwise excellent preservation of the fauna suggest that this lack of associations may be original.

The matrix of the biostrome was made up of micritic sediment with small (under 1 cm) fragments of fossil debris, largely made up of coral with occasional echinoderm (presumably crinoid) ossicles. While other studies (Perkins, 1963; Kissling and Lineback, 1967) noted additional faunal elements in the Coral Zone, they were not observed in the portion of the fossil bed examined in this study.

Discussion

The initial results of this study introduce several new facets to the interpretation of the paleoecology of the Coral Zone. Previous work by Kissling and Lineback (1967) determined an east/west orientation pattern to the specimens they examined on the fossil beds, whereas no clear pattern emerged in this study. The most notable differences between these two data sets is a result of the fact that Kissling and Lineback only considered branching favositid corals greater than 4 cm in size, and did not examine the solitary rugose corals, even though the current study indicates that they make up more than 67% of the total specimens. The lack of pattern among the specimens examined in this study may reveal that the fossils less than 4 cm in size are more likely to be moved by wave action rather than current direction, and therefore, have a more random orientation pattern. An additional complication is the occurrence of rugose corals that have a noticeable bend to their corallite. In such cases, two compass bearings were recorded but the specimen data were not included in the overall analysis of fossil orientation. The presence of these bending corals may be indicative of the alteration of growth position due to a change in water energy (Greb et al., 1993).

When fossils larger than 4 cm (inclusive of solitary rugose corals) were examined in this study, the orientation pattern produced by Kissling and Lineback was also not observed. It is possible that for some reason the area chosen for transect sampling did not exhibit the fossil orientation recognizable elsewhere on the bedding plane, or that the solitary rugose corals (>4 cm) responded differently to the hydrodynamic conditions as compared to the branching favositid corals, therefore producing different results. Additional fieldwork and analyses will be necessary to further explore why there is a discrepancy between the two studies.

An intriguing feature of the Coral Zone at the Falls of the Ohio is the lack of encrustation by sclerobionts, bioerosion, or other interactions besides coral/stromatoporoid associations. This observation is consistent with what was documented by Kissling and Lineback, and raises the question as to why a location with such high biodiversity and accumulation of skeletal material contains a paucity of ecological interactions, as well as low biodiversity of organisms other than corals or stromatoporoids. Future studies comparing the Falls of the Ohio biostrome to biostromes elsewhere in the world would be useful for determining if the types of interactions (and lack thereof) between organisms are typical for this type of assemblage.

Future Research Directions

The initial work presented herein reveals several intriguing observations regarding the paleoecology and paleoenvironment of the Coral Zone of the Falls of the Ohio. Specifically, two refined research questions have emerged: (1) What are the specific paleoenvironmental conditions that produced the biostrome at the Falls of the Ohio? (2) How typical (or atypical) is the paleoecology of the Coral Zone biostrome compared to other Devonian biostromes elsewhere in the world?

An additional field season is planned for the fall of 2018. Quadrat sampling using a 10 cm grid point counting method will be used to collect orientation data for fossils across a much larger area of the fossil beds. In addition to recording azimuth bearings for elongate fossils, the author Bulinski and her students plan to measure the bend angle of rugose corals across the field area to get a sense of how water energy may have been influencing the growth patterns and distributions of solitary rugose corals. Stromatoporoid/coral interactions will also be quantified. Lastly, to better compare the Falls of the Ohio locality to other stromatoporoid biostromes, a meta-analysis of Paleozoic biostrome paleoecology is planned as well.

ACKNOWLEDGMENTS

ACKNOWLEDGMENTS

ACKNOWLEDGMENTS

ACKNOWLEDGMENTS

ACKNOWLEDGMENTS

ACKNOWLEDGMENTS

ACKNOWLEDGMENTS

ACKNOWLEDGMENTS

ACKNOWLEDGMENTS

This field guide is dedicated to the memory of James E. Conkin, who was a mainstay of Tristate-area geology for many decades. Jim and his dedicated wife and collaborator, Barbara, made immense contributions to the understanding of stratigraphy and paleontology; we build on this great body of work.

This field guide is dedicated to the memory of James E. Conkin, who was a mainstay of Tristate-area geology for many decades. Jim and his dedicated wife and collaborator, Barbara, made immense contributions to the understanding of stratigraphy and paleontology; we build on this great body of work.

This field guide is dedicated to the memory of James E. Conkin, who was a mainstay of Tristate-area geology for many decades. Jim and his dedicated wife and collaborator, Barbara, made immense contributions to the understanding of stratigraphy and paleontology; we build on this great body of work.

This field guide is dedicated to the memory of James E. Conkin, who was a mainstay of Tristate-area geology for many decades. Jim and his dedicated wife and collaborator, Barbara, made immense contributions to the understanding of stratigraphy and paleontology; we build on this great body of work.

This field guide is dedicated to the memory of James E. Conkin, who was a mainstay of Tristate-area geology for many decades. Jim and his dedicated wife and collaborator, Barbara, made immense contributions to the understanding of stratigraphy and paleontology; we build on this great body of work.

This field guide is dedicated to the memory of James E. Conkin, who was a mainstay of Tristate-area geology for many decades. Jim and his dedicated wife and collaborator, Barbara, made immense contributions to the understanding of stratigraphy and paleontology; we build on this great body of work.

This field guide is dedicated to the memory of James E. Conkin, who was a mainstay of Tristate-area geology for many decades. Jim and his dedicated wife and collaborator, Barbara, made immense contributions to the understanding of stratigraphy and paleontology; we build on this great body of work.

This field guide is dedicated to the memory of James E. Conkin, who was a mainstay of Tristate-area geology for many decades. Jim and his dedicated wife and collaborator, Barbara, made immense contributions to the understanding of stratigraphy and paleontology; we build on this great body of work.

This field guide is dedicated to the memory of James E. Conkin, who was a mainstay of Tristate-area geology for many decades. Jim and his dedicated wife and collaborator, Barbara, made immense contributions to the understanding of stratigraphy and paleontology; we build on this great body of work.

We acknowledge fieldwork assistance and valuable discussions with C.D. Aucoin, G.C. Baird, A.J. Bartholomew, M.K. DeSantis, A. Goldstein, T.J. Malgieri, G.C. McIntosh, T.J. Schramm, C.E. Schwalbach, A.L. Young, and J.J. Zambito IV, among others. Special thanks go to C.E. Schwalbach for help with certain illustrations. CEB also acknowledges the help and support of B.L. Brett; his past research on Ordovician was supported by grants from the Petroleum Research Fund, American Chemical Society, from NSF grant 0819715, and a grant from the Hess Corporation. KVB would like to thank her undergraduate research students at Bellarmine University (most notably A. Burman, S. Hall, Z. Laughlin, K. Sadler, T. Summerlin, and A. Wilcox) for dedicating many hours to fieldwork, data processing, and data analysis as a part of their undergraduate research projects. Their curiosity, drive, and dedication have pushed this research effort in many novel directions, and it is a daily privilege to work alongside these enthusiastic future scientists. Our sincere appreciation to our reviewers, J.J. Zambito IV and A.M. Bancroft, for their constructive comments. Finally, this field trip and guide was co-sponsored by the Indiana Geological and Water Survey, the Ohio Department of Natural Resources Division of Geological Survey, and the North American Commission on Stratigraphic Nomenclature; we appreciate their support of our efforts. This publication is a contribution to International Geoscience Programme (IGCP) projects 591 and 653.

We acknowledge fieldwork assistance and valuable discussions with C.D. Aucoin, G.C. Baird, A.J. Bartholomew, M.K. DeSantis, A. Goldstein, T.J. Malgieri, G.C. McIntosh, T.J. Schramm, C.E. Schwalbach, A.L. Young, and J.J. Zambito IV, among others. Special thanks go to C.E. Schwalbach for help with certain illustrations. CEB also acknowledges the help and support of B.L. Brett; his past research on Ordovician was supported by grants from the Petroleum Research Fund, American Chemical Society, from NSF grant 0819715, and a grant from the Hess Corporation. KVB would like to thank her undergraduate research students at Bellarmine University (most notably A. Burman, S. Hall, Z. Laughlin, K. Sadler, T. Summerlin, and A. Wilcox) for dedicating many hours to fieldwork, data processing, and data analysis as a part of their undergraduate research projects. Their curiosity, drive, and dedication have pushed this research effort in many novel directions, and it is a daily privilege to work alongside these enthusiastic future scientists. Our sincere appreciation to our reviewers, J.J. Zambito IV and A.M. Bancroft, for their constructive comments. Finally, this field trip and guide was co-sponsored by the Indiana Geological and Water Survey, the Ohio Department of Natural Resources Division of Geological Survey, and the North American Commission on Stratigraphic Nomenclature; we appreciate their support of our efforts. This publication is a contribution to International Geoscience Programme (IGCP) projects 591 and 653.

We acknowledge fieldwork assistance and valuable discussions with C.D. Aucoin, G.C. Baird, A.J. Bartholomew, M.K. DeSantis, A. Goldstein, T.J. Malgieri, G.C. McIntosh, T.J. Schramm, C.E. Schwalbach, A.L. Young, and J.J. Zambito IV, among others. Special thanks go to C.E. Schwalbach for help with certain illustrations. CEB also acknowledges the help and support of B.L. Brett; his past research on Ordovician was supported by grants from the Petroleum Research Fund, American Chemical Society, from NSF grant 0819715, and a grant from the Hess Corporation. KVB would like to thank her undergraduate research students at Bellarmine University (most notably A. Burman, S. Hall, Z. Laughlin, K. Sadler, T. Summerlin, and A. Wilcox) for dedicating many hours to fieldwork, data processing, and data analysis as a part of their undergraduate research projects. Their curiosity, drive, and dedication have pushed this research effort in many novel directions, and it is a daily privilege to work alongside these enthusiastic future scientists. Our sincere appreciation to our reviewers, J.J. Zambito IV and A.M. Bancroft, for their constructive comments. Finally, this field trip and guide was co-sponsored by the Indiana Geological and Water Survey, the Ohio Department of Natural Resources Division of Geological Survey, and the North American Commission on Stratigraphic Nomenclature; we appreciate their support of our efforts. This publication is a contribution to International Geoscience Programme (IGCP) projects 591 and 653.

We acknowledge fieldwork assistance and valuable discussions with C.D. Aucoin, G.C. Baird, A.J. Bartholomew, M.K. DeSantis, A. Goldstein, T.J. Malgieri, G.C. McIntosh, T.J. Schramm, C.E. Schwalbach, A.L. Young, and J.J. Zambito IV, among others. Special thanks go to C.E. Schwalbach for help with certain illustrations. CEB also acknowledges the help and support of B.L. Brett; his past research on Ordovician was supported by grants from the Petroleum Research Fund, American Chemical Society, from NSF grant 0819715, and a grant from the Hess Corporation. KVB would like to thank her undergraduate research students at Bellarmine University (most notably A. Burman, S. Hall, Z. Laughlin, K. Sadler, T. Summerlin, and A. Wilcox) for dedicating many hours to fieldwork, data processing, and data analysis as a part of their undergraduate research projects. Their curiosity, drive, and dedication have pushed this research effort in many novel directions, and it is a daily privilege to work alongside these enthusiastic future scientists. Our sincere appreciation to our reviewers, J.J. Zambito IV and A.M. Bancroft, for their constructive comments. Finally, this field trip and guide was co-sponsored by the Indiana Geological and Water Survey, the Ohio Department of Natural Resources Division of Geological Survey, and the North American Commission on Stratigraphic Nomenclature; we appreciate their support of our efforts. This publication is a contribution to International Geoscience Programme (IGCP) projects 591 and 653.

We acknowledge fieldwork assistance and valuable discussions with C.D. Aucoin, G.C. Baird, A.J. Bartholomew, M.K. DeSantis, A. Goldstein, T.J. Malgieri, G.C. McIntosh, T.J. Schramm, C.E. Schwalbach, A.L. Young, and J.J. Zambito IV, among others. Special thanks go to C.E. Schwalbach for help with certain illustrations. CEB also acknowledges the help and support of B.L. Brett; his past research on Ordovician was supported by grants from the Petroleum Research Fund, American Chemical Society, from NSF grant 0819715, and a grant from the Hess Corporation. KVB would like to thank her undergraduate research students at Bellarmine University (most notably A. Burman, S. Hall, Z. Laughlin, K. Sadler, T. Summerlin, and A. Wilcox) for dedicating many hours to fieldwork, data processing, and data analysis as a part of their undergraduate research projects. Their curiosity, drive, and dedication have pushed this research effort in many novel directions, and it is a daily privilege to work alongside these enthusiastic future scientists. Our sincere appreciation to our reviewers, J.J. Zambito IV and A.M. Bancroft, for their constructive comments. Finally, this field trip and guide was co-sponsored by the Indiana Geological and Water Survey, the Ohio Department of Natural Resources Division of Geological Survey, and the North American Commission on Stratigraphic Nomenclature; we appreciate their support of our efforts. This publication is a contribution to International Geoscience Programme (IGCP) projects 591 and 653.

We acknowledge fieldwork assistance and valuable discussions with C.D. Aucoin, G.C. Baird, A.J. Bartholomew, M.K. DeSantis, A. Goldstein, T.J. Malgieri, G.C. McIntosh, T.J. Schramm, C.E. Schwalbach, A.L. Young, and J.J. Zambito IV, among others. Special thanks go to C.E. Schwalbach for help with certain illustrations. CEB also acknowledges the help and support of B.L. Brett; his past research on Ordovician was supported by grants from the Petroleum Research Fund, American Chemical Society, from NSF grant 0819715, and a grant from the Hess Corporation. KVB would like to thank her undergraduate research students at Bellarmine University (most notably A. Burman, S. Hall, Z. Laughlin, K. Sadler, T. Summerlin, and A. Wilcox) for dedicating many hours to fieldwork, data processing, and data analysis as a part of their undergraduate research projects. Their curiosity, drive, and dedication have pushed this research effort in many novel directions, and it is a daily privilege to work alongside these enthusiastic future scientists. Our sincere appreciation to our reviewers, J.J. Zambito IV and A.M. Bancroft, for their constructive comments. Finally, this field trip and guide was co-sponsored by the Indiana Geological and Water Survey, the Ohio Department of Natural Resources Division of Geological Survey, and the North American Commission on Stratigraphic Nomenclature; we appreciate their support of our efforts. This publication is a contribution to International Geoscience Programme (IGCP) projects 591 and 653.

We acknowledge fieldwork assistance and valuable discussions with C.D. Aucoin, G.C. Baird, A.J. Bartholomew, M.K. DeSantis, A. Goldstein, T.J. Malgieri, G.C. McIntosh, T.J. Schramm, C.E. Schwalbach, A.L. Young, and J.J. Zambito IV, among others. Special thanks go to C.E. Schwalbach for help with certain illustrations. CEB also acknowledges the help and support of B.L. Brett; his past research on Ordovician was supported by grants from the Petroleum Research Fund, American Chemical Society, from NSF grant 0819715, and a grant from the Hess Corporation. KVB would like to thank her undergraduate research students at Bellarmine University (most notably A. Burman, S. Hall, Z. Laughlin, K. Sadler, T. Summerlin, and A. Wilcox) for dedicating many hours to fieldwork, data processing, and data analysis as a part of their undergraduate research projects. Their curiosity, drive, and dedication have pushed this research effort in many novel directions, and it is a daily privilege to work alongside these enthusiastic future scientists. Our sincere appreciation to our reviewers, J.J. Zambito IV and A.M. Bancroft, for their constructive comments. Finally, this field trip and guide was co-sponsored by the Indiana Geological and Water Survey, the Ohio Department of Natural Resources Division of Geological Survey, and the North American Commission on Stratigraphic Nomenclature; we appreciate their support of our efforts. This publication is a contribution to International Geoscience Programme (IGCP) projects 591 and 653.

We acknowledge fieldwork assistance and valuable discussions with C.D. Aucoin, G.C. Baird, A.J. Bartholomew, M.K. DeSantis, A. Goldstein, T.J. Malgieri, G.C. McIntosh, T.J. Schramm, C.E. Schwalbach, A.L. Young, and J.J. Zambito IV, among others. Special thanks go to C.E. Schwalbach for help with certain illustrations. CEB also acknowledges the help and support of B.L. Brett; his past research on Ordovician was supported by grants from the Petroleum Research Fund, American Chemical Society, from NSF grant 0819715, and a grant from the Hess Corporation. KVB would like to thank her undergraduate research students at Bellarmine University (most notably A. Burman, S. Hall, Z. Laughlin, K. Sadler, T. Summerlin, and A. Wilcox) for dedicating many hours to fieldwork, data processing, and data analysis as a part of their undergraduate research projects. Their curiosity, drive, and dedication have pushed this research effort in many novel directions, and it is a daily privilege to work alongside these enthusiastic future scientists. Our sincere appreciation to our reviewers, J.J. Zambito IV and A.M. Bancroft, for their constructive comments. Finally, this field trip and guide was co-sponsored by the Indiana Geological and Water Survey, the Ohio Department of Natural Resources Division of Geological Survey, and the North American Commission on Stratigraphic Nomenclature; we appreciate their support of our efforts. This publication is a contribution to International Geoscience Programme (IGCP) projects 591 and 653.

We acknowledge fieldwork assistance and valuable discussions with C.D. Aucoin, G.C. Baird, A.J. Bartholomew, M.K. DeSantis, A. Goldstein, T.J. Malgieri, G.C. McIntosh, T.J. Schramm, C.E. Schwalbach, A.L. Young, and J.J. Zambito IV, among others. Special thanks go to C.E. Schwalbach for help with certain illustrations. CEB also acknowledges the help and support of B.L. Brett; his past research on Ordovician was supported by grants from the Petroleum Research Fund, American Chemical Society, from NSF grant 0819715, and a grant from the Hess Corporation. KVB would like to thank her undergraduate research students at Bellarmine University (most notably A. Burman, S. Hall, Z. Laughlin, K. Sadler, T. Summerlin, and A. Wilcox) for dedicating many hours to fieldwork, data processing, and data analysis as a part of their undergraduate research projects. Their curiosity, drive, and dedication have pushed this research effort in many novel directions, and it is a daily privilege to work alongside these enthusiastic future scientists. Our sincere appreciation to our reviewers, J.J. Zambito IV and A.M. Bancroft, for their constructive comments. Finally, this field trip and guide was co-sponsored by the Indiana Geological and Water Survey, the Ohio Department of Natural Resources Division of Geological Survey, and the North American Commission on Stratigraphic Nomenclature; we appreciate their support of our efforts. This publication is a contribution to International Geoscience Programme (IGCP) projects 591 and 653.

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