Pyrite framboid diameters were examined in 31 samples taken from 2 Marcellus Shale cores recovered from Greene County, Pennsylvania, and Upshur County, West Virginia (USA). Analysis of framboid diameters in those samples from the more proximally located Upshur County core suggests that anoxic to anoxic-euxinic conditions persisted during accumulation of the transgressive-regressive cycle (MSS1) that comprises the Union Springs Member of the Marcellus Shale, with intermittent episodes of dysoxia. An increased abundance of large framboids documented from the overlying transgressive-regressive cycle (MSS2), which comprises the bulk of the Oatka Creek Member of the Marcellus Shale, indicates improved bottom-water conditions. Redox conditions recorded by framboid diameters of the MSS1 cycle of the Greene County core are generally similar to those of the Upshur County core; however, conditions in that region of the basin from which the Greene County core was recovered appear to have remained dominantly anoxic to anoxic-euxinic. Furthermore, the presence of small syngenetic framboids and large diagenetic framboids in the same thin section samples suggests that redox conditions fluctuated on a temporal scale beyond that observed at the scale of a centimeter-scale thin section. Framboid diameter trends established for both cores enhance our understanding of how much redox conditions varied both spatially and stratigraphically during accumulation of the Marcellus Shale.

ABSTRACT Beautifully fossiliferous strata in the Hamilton Group (Middle Devonian, central New York) constitute a rich “ecological archive” sufficient to probe and test foundational concepts in paleontology. The evident community stability of Hamilton faunas over 4–6 m.y.—including two proposed mechanisms for coordinated stasis—has ignited controversy. Resolving community structure and both taxonomic and ecological temporal persistence within the Hamilton Group thus becomes critical to testing whether these Hamilton communities are stable and whether they are ecologically “locked.” Toward this end, we conducted multivariate analyses (cluster and correspondence analysis) of marine faunas in 81 large samples (~300 specimens each) in shallowing-upward sequences of the Cardiff and Pecksport Members (Marcellus Subgroup, Oatka Creek Formation) of the Hamilton Group. Eight statistically and ecologically distinctive benthic communities characterize the vertical gradient, from depauperate, deeper-water dark shales below to species-rich shelf siltstones above. These communities correlate strongly with grain size, bioturbation intensity, bedding thickness, density of fossils, and faunal and ecological diversity. Species richness varies inversely with weight percent organic matter. We characterized taxonomic distributions using multivariate statistics; these statistical analyses were based on percentages of 50 taxa. In order of decreasing depth, the communities are: Cephalopod- Pterochaenia , Pterochaenia-Eumetabolotoechia , Eumetabolotoechia , Emanuella , Eumetabolotoechia-Ambocoelia , Arcuaminetes-Eumetabolotoechia , Arcuaminetes-Ambocoelia , and Mucrospirifer- Ambocoelia . The Cephalopod- Pterochaenia community represents a mixed benthic-pelagic fauna associated with the deepest and finest-grained facies. The Pterochaenia-Eumetabolotoechia , Eumetabolotoechia , and Emanuella communities have low to moderate species richness and are dominated by epifaunal, active suspension feeders, especially the small epibyssate bivalve Pterochaenia fragilis , and the pedunculate brachiopods Eumetabolotoechia multicostata and Emanuella subumbona . The Pterochaenia-Eumetabolotoechia community is an opportunistic fauna that developed when the substrate first became favorable for colonization by benthic organisms. To a lesser extent, this probably also holds true for the Eumetabolotoechia assemblage. Communities near the top of the shallowing-upward cycle— Eumetabolotoechia- Ambocoelia , Arcuaminetes-Eumetabolotoechia , Arcuaminetes-Ambocoelia , and Mucrospirifer-Ambocoelia —have higher taxonomic and ecological heterogeneity, with a more diverse array of trophic and locomotory groups than their counterparts in the finer-grained, and inferred deeper, facies. Cluster significance tests applied to all pairs of communities known from adequate numbers of samples demonstrated that the communities are statistically valid and distinctive. Multivariate means of all communities were significantly different; furthermore, most pairs of communities were drawn from populations that showed no overlap in terms of rectangular distributions. The community sequence and an ordination derived from the first two axes of the correspondence analysis provided relative depth curves. Our communities, with two exceptions, do not have clear counterparts among upper Hamilton Group faunas. The ecological locking model proposed to explain the stability of Hamilton faunas is not supported by our quantitative tests to date.

Abstract An integrated approach, involving nearly all available biostratigraphic data, event and sequence stratigraphy, has been utilized in correlation of the Middle Devonian (latest Eifelian–Givetian) Hamilton Group and equivalent strata in north-central North America. This approach permits high-resolution correlation of strata equivalent to the Oatka Creek (upper Marcellus), Skaneateles, Ludlowville and Moscow Formations from New York into sections bordering the Michigan Basin in Ontario, Canada, as well as southern Michigan, northern Ohio and Indiana, USA. Most member and submember-scale units, herein slightly redefined and interpreted as 3rd and 4th order sequences, respectively, and their bounding condensed beds can be correlated regionally. Moreover, many faunal patterns also persist across this region, which, together with sequence stratigraphy, provides a bridge for correlation into the Michigan Basin. The detailed stratigraphy presented herein permits a more-resolved understanding of far-field tectonics, eustasy and biotic responses during the Middle Devonian. Allocyclic processes, primarily eustasy, played a key role in generating persistent sedimentary cycles. Episodes of rapid mud sedimentation occurred over large areas of the cratonic interior, distal to Acadian source terrains. The major Algonquin–Findlay Arch, which presently separates the Michigan Basin from the Appalachian foreland basin, was not present during deposition of these strata. Conversely, a roughly north–south trending region, running approximately through present-day Cleveland, Ohio, was first a local subsiding area during late Eifelian–early Givetian time and then underwent topographic inversion to form a local arch at which upper Hamilton units were condensed and then bevelled during the later Givetian; we infer that this feature may represent a migrating forebulge. Finally, fossil biotas do not show strong partitioning into Appalachian and Michigan basin faunal subprovinces during the early Givetian, as there appears to have been no physical barrier to migration at least in the study area. However, Hamilton-equivalent strata in the most proximal portion of the Appalachian Basin do show a relatively minor admixture of typical Michigan Basin taxa with normal Hamilton forms.

Abstract The late Eifelian–earliest Givetian interval (Middle Devonian) represents a time of significant faunal turnover in the eastern Laurentia and globally. A synthesis of biostratigraphic, K-bentonite and sequence stratigraphic data indicates that physical and biotic events in the Appalachian foreland basin sections in New York are coeval with the predominantly carbonate platform sections of southern Ontario and Ohio. The upper Eifelian ( australis to ensensis conodont zones) Marcellus Subgroup in New York comprises two large-scale (3rd-order) composite depositional sequences dominated by black shale, which are here assigned to the Union Springs and Oatka Creek Formations. The succession includes portions of three distinctive benthic faunas or ecological–evolutionary sub-units (EESUs): ‘Onondaga’, ‘Stony Hollow’ and ‘Hamilton’. In the northern Appalachian Basin in New York, the boundaries of these bioevents show evidence of abrupt, widespread extinctions, immigration and ecological restructuring. In the Niagara Peninsula of Ontario and from central to northern Ohio, the same sequence stratigraphic pattern and bioevents are recognized in coeval, carbonate-dominated facies. The correlations underscore a relatively simple pattern of two major sequences and four subsequences that can be recognized throughout much of eastern Laurentia. Moreover, the biotic changes appear to be synchronous across the foreland basin and adjacent cratonic platform. However, the degree of change differs substantially, being less pronounced in carbonatedominated mid-continent sections. Finally, we make the case that the two major faunal changes align with regional sequence stratigraphic patterns as well as with the global Kačák bioevents.

Abstract New data compilations for successive formation scale intervals, approximately third-order sequences, permit a statistical characterization of the ecological–evolutionary subunits (EESUs) or faunas of the Latest Silurian to mid-Late Devonian interval in the Appalachian Basin. Cluster analysis using the Jaccard coefficient of similarity show that certain formations cluster tightly together on the basis of faunal composition while in other cases units are sharply set off from superseding units. This result indicates both the coherence of faunal composition within EESUs and the discreteness of their boundaries. The results also require minor revision of EESUs previously delineated, including the addition of three new units. The Esopus Formation is designated as a distinct unit separate from the Schoharie on the basis of brachiopods from shallow water facies of the Skunnemunk outlier in New York; in addition, a short-lived Stony Hollow fauna is recognized in shallow shelf facies of the Union Springs Formation and coeval units (formerly referred to as the lower Marcellus Formation) and the lower transgressive beds of the overlying Oatka Creek Formation. This fauna, consisting of subtropical Old World Realm (OWR) emigrants, is distinctive from both the underlying Onondaga fauna and that of the overlying Hamilton Group. Moreover, the Tully Formation presents another case of a short-lived incursion of tropical OWR taxa followed by the extermination of this fauna and reappearance of a suite of typically Hamilton taxa. This case illustrates that EESUs may persist globally despite their local extermination or emigration from a large region, such as the Appalachian Basin. Review of the broader context of EESU turnover suggests that these crises are geologically rapid and synchronous. Moreover, most of the Devonian EESU boundaries coincide with recognized global bioevents, within the limits of combined biostratigraphic and sequence stratigraphic resolution. Hence, these crises, although perhaps locally accentuated in the Appalachian Basin, are allied to global causes. They appear mostly to be associated with rapid rises in sea level, periods of widespread climatic change and hypoxic events in basinal areas.

Abstract The recent development of unconventional oil and natural gas resources in the United States builds upon many decades of research, which included resource assessment and the development of well completion and extraction technology. The Eastern Gas Shales Project, funded by the U.S. Department of Energy in the 1980s, investigated the gas potential of organic-rich, Devonian black shales in the Appalachian, Michigan, and Illinois basins. One of these eastern shales is the Middle Devonian Marcellus Shale, which has been extensively developed for natural gas and natural gas liquids since 2007. The Marcellus is one of the basal units in a thick Devonian shale sedimentary sequence in the Appalachian basin. The Marcellus rests on the Onondaga Limestone throughout most of the basin, or on the time-equivalent Needmore Shale in the southeastern parts of the basin. Another basal unit, the Huntersville Chert, underlies the Marcellus in the southern part of the basin. The Devonian section is compressed to the south, and the Marcellus Shale, along with several overlying units, grades into the age-equivalent Millboro Shale in Virginia. The Marcellus-Millboro interval is far from a uniform slab of black rock. This field trip will examine a number of natural and engineered exposures in the vicinity of the West Virginia–Virginia state line, where participants will have the opportunity to view a variety of sedimentary facies within the shale itself, sedimentary structures, tectonic structures, fossils, overlying and underlying formations, volcaniclastic ash beds, and to view a basaltic intrusion.