ABSTRACT Glaciogenic rocks are rare in the Appalachian area and occur only locally as parts of Upper Precambrian and Upper Devonian successions. This trip examines a relatively recent exposure of Upper Devonian glaciogenic diamictites and laminites along Corridor H (U.S. Highway 48) in east-central West Virginia, USA. The diamictites occur in the Rockwell Member of the Price Formation, in transition with the underlying redbeds of the Upper Devonian Hampshire Formation. Palynology indicates that all parts of the Rockwell Member exposed at the locality are present in the Retispora lepidophyta – Verrucosisporites nitidus (LN) Miospore Biozone and are, therefore, of Late Devonian, but not latest Devonian, age. This biozone occurrence indicates correlation with parts of the Oswayo Member of the Price Formation, the Finzel tongue of the Rockwell Formation, and with dropstone-bearing parts of the Cleveland Shale Member of the Ohio Shale in northeastern Kentucky. Much previous work supports a glaciogenic origin for the diamictites and associated sediments, which occur as parts of a shallow-marine incursion that ended the Hampshire/Catskill alluvial-plain/deltaic complex across much of the Central Appalachian area. The glaciogenic succession is part of nearshore, marginal-marine strata that accumulated in an embayment during the Cleveland-Oswayo-Finzel transgression, which represents a global eustatic sea-level rise and foreland subsidence related to Acadian/Neoacadian deformational loading in the adjacent orogen. Detrital-zircon-provenance data from the diamictites indicate Ordovician plutonic sources as well as reworked Neoproterozoic to Ordovician sedimentary sources that can only have been derived from nearby Inner Piedmont sources like the Potomac terrane. This provenance suggests that Acadian/Neoacadian convergence of the exotic Carolina terrane with the New York and Virginia promontories along the southeastern margin of Laurussia not only uplifted Inner Piedmont source areas into a high mountain range capable of supporting glaciation in a subtropical setting, but also, through deformational loading, enhanced regional subsidence and the incursion of shallow seas that allowed alpine glaciers access to the open sea.

ABSTRACT A 3 ton (2.7 metric tonnes [t]), granitoid lonestone with Appalachian provenance was found in situ in offshore Devonian black shale in northeastern Kentucky, United States, and is denoted herein as the Robinson boulder, or lonestone, after its discoverer, Michael J. Robinson. This large boulder appears to have been displaced nearly 500 km from its source on the opposite margin of the Acadian/Neoacadian Appalachian foreland basin. While previous identifications of possible lonestones have been attributed to Pleistocene glacial events, scrutiny of this lonestone’s origin suggests that the boulder, which was embedded in the Upper Devonian Cleveland Shale Member of the Ohio Shale in northeastern Kentucky, is most likely a Devonian ice-rafted glacial dropstone. Notably, palynologic correlation with reported glacial diamictites elsewhere in the basin indicates such a source. Together, the dropstone and diamictites, separated by ~500 km, provide evidence for alpine glaciation in the ancient Acadian/Neoacadian orogen and for tidewater glaciers in the adjacent, eastern margin of the foreland basin. The latest Devonian marine transgression and Neoacadian foreland subsidence are interpreted to have been associated with tidewater glacial connections to the open sea. Importantly, the existence of this dropstone and its likely glacial precursor events require new considerations about contemporary black-shale sedimentation and the influence of tectonics on the delivery of glacial sediments to foreland basins.

ABSTRACT During latest Devonian to Middle Mississippian parts of the Neoacadian and Ouachita orogenies, the Appalachian Basin and parts of the Illinois Basin were filled with clastic debris derived from the westward-prograding Borden-Grainger-Price-Pocono clastic wedge. This delta complex is overlain by the widespread shallow-water Newman–Greenbrier–Slade–St. Louis–Warsaw–Salem–Harrodsburg carbonate interval across sediment-starved surfaces, comprising the Floyds Knob bed or interval. The Middle Mississippian (late Osagean; early Viséan) Floyds Knob interval is less than a meter to several meters thick and is composed of multiple zones of pelletal glauconite, finely divided glauconitic shales, glauconitic carbonates, and locally derived carbonate mud mounds. The interval occurs across most of the Borden-Grainger delta platform, delta front, prodelta, and within the starved-basin area seaward of the delta complex, which was then filled with the Fort Payne Formation. This study reports herein the first occurrence of the Floyds Knob interval within the Fort Payne Formation. Glauconite deposition in this interval apparently occurred in mildly oxic to dysoxic, sediment-starved, shallow-marine settings and is believed to represent termination of major clastic influx in more proximal parts of the Neoacadian foreland basin during lowstand conditions. Moreover, these starved-basin conditions can be correlated with delta diversion following bulge migration during flexural loading–type relaxation. During these sediment-starved, lowstand conditions, glauconite was deposited across deltaic and basinal settings in central and distal parts of the Neoacadian foreland basin, as well as in eastern parts of the present-day Illinois intracratonic basin. The cessation of deltaic clastic sedimentation permitted development of carbonate mud mounds and associated glauconitic shales on and near reactivated structures in central parts of the Fort Payne starved basin and set the stage for the widespread deposition of thick, Meramecian–Chesterian carbonates throughout the basins during succeeding subtropical and lowstand conditions. Whether less-than-a-meter or tens-of-meters thick, the Floyds Knob interval is a widespread Middle Mississippian chronostratigraphic interval in the east-central United States that reflects a change in tectonic regime, which is recorded in the shift from predominantly clastic to carbonate sedimentation across a broad region. Aside from its correlative value, the unit demonstrates consequent sedimentary responses to the interplay among tectonism, paleoclimate, and paleogeography.

ABSTRACT This trip explores three different occurrences of a diamictite-bearing unit in the transition between Upper Devonian redbeds of the Hampshire Formation (alluvial and fluvial deposits) and Mississippian sandstones and mudstones of the Price/Pocono Formations (deltaic deposits). Palynology indicates that all the diamictites examined are in the LE and LN miospore biozones, and are therefore of Late Devonian, but not latest Devonian, age. Their occurrence in these biozones indicates correlation with the Cleveland Member of the Ohio Shale, Oswayo Member of the Price Formation, and Finzel tongue of the Rockwell Formation in the central Appalachian Basin and with a large dropstone (the Robinson boulder) in the Cleveland Member of the Ohio Shale in northeastern Kentucky. Although several lines of evidence already support a glaciogenic origin for the diamictites, the coeval occurrence of the dropstone in open-marine strata provides even more convincing evidence of a glacial origin. The diamictites are all coeval and occur as parts of a shallow-marine incursion that ended Hampshire/Catskill alluvial-plain accumulation in most areas; however, at least locally, alluvial redbed accumulation continued after diamictite deposition ended. The diamictites are parts of nearshore, marginal-marine strata that accumulated during the Cleveland-Oswayo-Finzel transgression, which is related to global eustasy and to foreland deformational loading during the late Acadian orogeny. Detrital zircon data from clasts in a diamictite at Stop 3 (Bismarck, West Virginia) indicate likely Inner Piedmont, Ordovician plutonic sources and suggest major Acadian uplift of Inner Piedmont sources during convergence of the exotic Carolina terrane with the New York and Virginia promontories. Hence, the Acadian orogeny not only generated high mountain source areas capable of supporting glaciation in a subtropical setting, but also through deformational foreland loading, abetted regional subsidence and the incursion of shallow seas that allowed mountain glaciers access to the open sea.

Abstract Black shales are integral parts of most foreland-basin deposits and, because they typically reflect maximum basin subsidence, their distributions serve as proxies for the extent of foreland-basin development. In the United States Appalachian area, the distribution of Middle–Upper Ordovician black shales suggests that the Taconian Orogeny proceeded from south to north along the eastern Laurentian margin and that Taconian tectophases were mediated by convergence at continental promontories. In the Late Ordovician Taconic tectophase, changes in the distribution of the Martinsburg and Utica black shales support a reversal of subduction polarity that effected the reactivation of basement structures and basin migration sufficient to yoke the Appalachian foreland basin with adjacent intracratonic basins. Shale distribution suggests that early Chatfieldian (late Sandbian–early Katian), east-verging subduction early in the tectophase generated a cratonic extensional regime with a narrow foreland basin that developed along reactivated Iapetan basement structures. Abruptly, in late Chatfieldian–early Edenian (early Katian) time, westwards migration of basinal Utica black shales and an underlying unconformity suggests change to a compressional regime and westwards subduction vergence. The coincidence of changes in basin shape and migration with the shifts in subduction polarity suggests a causal relationship.

Abstract Recent plays like the Middle Devonian Marcellus Shale and possible prospects like the Upper Ordovician Utica Shale point out the significance of dark-shale source rocks in the Appalachian Basin. Mapping the distribution of such shales in space and time throughout the basin shows that periods of dark-shale deposition coincided with orogenies and the related formation of foreland basins. The fact that foreland basins form and become repositories for organic-rich dark-shale source rocks is mostly the result of deformational loading in the adjacent orogen. Tectonism mostly exerts its control through the flexural effects of deformational loading and subsequent relaxation in the orogen. These flexural processes generate sedimentary responses in the foreland basin that are reflected in a seven-part unconformity-bound cycle, of which dark shales are a major component. Because orogenies comprise a series of smaller deformational events, or tectophases, and each tectophase generates a similar cycle, many foreland basins typically exhibit a cyclic array of dark-shale and intervening clastic units, called tectophase cycles. Thirteen such third-order tectophase cycles, formed during four orogenies, are present in the Appalachian Basin. Using examples of foreland-basin dark-shale units formed during the Ordovician-Silurian Taconian and Devonian-Mississippian Acadian/Neoacadian orogenies, the timing of cycles and migration of successive dark-shale units within them relative to the progress of orogeny are presented as evidence of causal relationships between tectonism and dark-shale sedimentation. However, tectonic influence may extend well beyond the confines of the foreland basin in the form of far-field tensional and compressional forces. This may impel the yoking of foreland and intracratonic basins as well as the reactivation of foreland basement structures—the former allowing dark-shale depositional conditions to move from one basin to the other, and the latter, inaugurating new basins for dark-shale accumulation.

Abstract In latest Devonian time, the collision between Avalonia, the New York promontory and Carolina terrane under the impact of Gondwana, generated an orogeny that began in New England and migrated southward in time. Once thought to be the fourth tectophase of the Acadian orogeny, this event is now called the Neoacadian orogeny. Active deformational loading during the event initially produced the Sunbury black-shale basin, whereas subsequent relaxational phases produced the Borden-Grainger-Price-Pocono and Pennington–Mauch Chunk clastic wedges, which largely reflect the dextral transpressional docking of the Carolina terrane against the Virginia promontory and points southward. The Sunbury black-shale basin and the infilling clastic wedges are among the thickest and most extensive in the Appalachian foreland basin. This trip will demonstrate differences in basinal black-shale and deltaic infilling of the foreland basin, both in more active, proximal and in more distal, sediment-starved parts of the basin. In particular, we will examine relationships between sedimentation and tectonism in the Early-Middle Mississippian Sunbury/Borden/Grainger/Fort Payne delta/basin system in the western Appalachian Basin during the Neoacadian Orogeny. We will emphasize the interrelated aspects of delta sedimentation, basin starvation, and mud-mound genesis on and near the ancient Borden-Grainger delta front. Temporal constraints are provided by the underlying Devonian-Mississippian black shales and by the widespread Floyds Knob Bed/zone, a dated glauconite/phosphorite interval that occurs across the distal delta/basin complex.

In mid-Mohawkian time at the Turinian–Chatfieldian (Blackriverian–Trenton) transition, the extensive, shallow-, warm-water Blackriverian carbonate platform, in a low-latitude, subtropical setting across east-central Laurentia, underwent an abrupt change to temperate-water, sedimentary and faunal regimes. The change occurs across a regional unconformity, the formation of which is coincident with inception of a major Taconian tectophase and the related breakup of the Blackriverian Platform along old zones of structural weakness into smaller and higher platforms and shelves separated by a linear low area called the Sebree Trough . This breakup is interpreted to reflect far-field, foreland deformation, and temperate-water carbonates soon predominated across the resulting shelves and platforms, some 1000 km from the nearest open continental margin. Yet, paleogeographic models, the presence of warm-water carbonates distal to the trough as well as warm-water faunal and lithologic inliers in protected back-shoal settings on the Lexington Platform still indicate the presence of warm surface waters in a subtropical setting. Most interpretations support the necessity of upwelling from the Sebree Trough to explain this seeming anomaly, reflecting the significance of coeval tectonism in generating necessary conditions for the upwelling. Others have called upon glaciation for generating cooler oceanic waters and the enhanced oceanic circulation that would have developed coastal upwelling, sufficiently intense and widespread to have penetrated far across the open continental margin. Although latest Ordovician Hirnantian glaciation is well supported, evidence for the timing, extent, and likelihood of earlier Late Ordovician (Chatfieldian) glaciation is uncertain and contradictory. Although it is not possible to preclude the effects of such glaciation, the synergetic effects of tectonics and paleogeography may offer a more plausible explanation for upwelling during the time of syn-Taconic, far-field, foreland deformation on southeastern Laurentia; these effects may have even accentuated any glacial influence. Inasmuch as the Late Ordovician was a time of global tectonism, there may have been other low-latitude Ordovician cratonic settings in which changes in nearby orogens offer explanations for abrupt changes in sedimentary and faunal regimes on the adjacent forelands.

The chemostratigraphic (δ 13 C carb ) record of the Lexington Limestone in central Kentucky is a high-resolution record in Chatfieldian and lower Edenian strata. Parts of the Lexington Limestone in this region reflect an anomalous structurally controlled carbonate buildup with complex facies relationships. Chemostratigraphic analysis of buildup and off-buildup composite sections, which exemplify the Lexington facies mosaic, reveals an overall decreasing trend in 13 C compositions throughout the formation and into the overlying Clays Ferry Formation. Superimposed on this trend are four locally correlative excursions. The most significant excursion is found within the Logana Member. The Guttenberg excursion is locally expressed as two prominent δ 13 C peaks (maxima +2.58‰). The excursion is important because of its stratigraphic position above the regional and globally correlated Millbrig K-bentonite, which allows for correlation with chronostratigraphically equivalent successions. The ubiquity of the Guttenberg excursion has been recognized throughout the eastern and central United States and the Baltic region. Additional excursions have been detected and are common in other sections, showing that the chemostratigraphic record of the Lexington Limestone is similar in buildup and off-buildup sections, even across complex lithofacies boundaries. The similarity of the record across complex facies, moreover, suggests that these localized excursions are “events,” which can be used to constrain correlations and augment known facies relationships. Furthermore, the overall chemostratigraphic trend in the Lexington Limestone appears similar to published δ 13 C values from equivalent strata in Baltoscandia, emphasizing the global correlative value of chemostratigraphic trends in Upper Ordovician strata.

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Full article available in PDF version.

Full article available in PDF version.

Full article available in PDF version.

Full article available in PDF version.

Full article available in PDF version.

Full article available in PDF version.