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| Ohio Shale | |
|---|---|
| Name | Ohio Shale |
| Type | Formation |
| Age | Late Devonian |
| Period | Devonian |
| Primary lithology | Shale |
| Other lithology | Black shale, siltstone, limestone nodules |
| Region | Ohio, Indiana, Kentucky, West Virginia, Pennsylvania |
| Country | United States |
Ohio Shale is a Late Devonian black shale formation recognized in the Appalachian Basin across Ohio, Indiana, Kentucky, West Virginia, and Pennsylvania. It is noted for organic-rich sediment, fossil assemblages tied to the Frasnian–Famennian boundary, and its role in regional stratigraphy correlated with units studied in the Michigan Basin and along the Allegheny Front. The unit has been central to research by institutions such as the United States Geological Survey, Ohio Geological Survey, and universities including Ohio State University, West Virginia University, and Kentucky Geological Survey.
The formation lies within the Appalachian Basin, bounded by structural features like the Cincinnati Arch, the Findlay Arch, and the Rome Trough, and it overlies units such as the Cuyahoga Formation and underlies strata correlated with the Huron Shale and Caney Shale. Regional mapping by the Illinois State Geological Survey and the Pennsylvania Geological Survey places the unit in lithostratigraphic frameworks associated with the Late Devonian marine transgression documented across the Central Appalachian Basin and the Michigan Basin. Stratigraphic analyses reference biostratigraphic markers tied to conodont zones defined by researchers from institutions like the Smithsonian Institution and the American Museum of Natural History.
The succession consists predominantly of organic-rich dark-gray to black laminated shale with interbeds of siltstone, thin limestones, and intermittent pyritic horizons investigated by teams at Harvard University, Yale University, and University of Michigan. Mineralogical studies cite high total organic carbon (TOC) and kerogen types similar to those characterized in Barnett Shale, Marcellus Formation, and New Albany Shale. Mineralogy descriptions reference clay minerals such as illite and smectite studied by researchers from Massachusetts Institute of Technology and Stanford University, alongside authigenic carbonates and sulfides examined by chemists affiliated with Argonne National Laboratory.
Fossil content includes conodonts, brachiopods, trilobites, chondrichthyan scales, and mollusks, with paleontological work contributed by curators at the Field Museum, American Museum of Natural History, and the Royal Ontario Museum. Conodont assemblages used for biostratigraphy include taxa correlated with zones described by Maurice Ellison-style frameworks and compared to faunas from Givetian–Frasnian sequences in Europe and China. Organic-walled microfossils and palynomorphs have been reported in studies involving the Paleontological Society and researchers from University of Cincinnati. Exceptional preservation of soft-bodied elements in some intervals has drawn comparison to Lagerstätten like the Hunsrück Slate and has been discussed at conferences sponsored by the Geological Society of America.
Radiometric and biostratigraphic studies place the unit in the Late Devonian, primarily the Frasnian to Famennian stages, correlating with extinction events documented in literature by authors associated with Oxford University, Cambridge University, and Princeton University. Correlation efforts link the unit to equivalents such as the Marcellus Shale in the Appalachian Basin and the Dahmer Formation-style units in the Michigan Basin, using conodont zonation established in monographs from the International Commission on Stratigraphy. Chemostratigraphic correlations employing carbon isotope excursions reference work by researchers at University College London and ETH Zurich.
The black, organic-rich intervals are analogous to source rocks like the Barnett Shale and Marcellus Formation and have been evaluated for shale-gas potential by energy companies including ExxonMobil, Chevron, and smaller independents, as well as by the Energy Information Administration and the United States Geological Survey. Historical petroleum seeps and oil shows documented by the American Petroleum Institute and state surveys led to sampling campaigns by Shell, BP, and academic collaborators at Penn State University. Resource assessments consider TOC, thermal maturity measured via vitrinite reflectance techniques developed at U.S. Department of Energy laboratories, and reservoir properties comparable to plays in the Powell Basin and Antrim Shale.
Interpretations favor deposition in an anoxic to dysoxic outer shelf to basinal setting during a major marine transgression linked to global sea-level changes considered in syntheses by J. D. Milliman-style researchers and paleoceanographers at Scripps Institution of Oceanography. Geochemical proxies including trace-metal enrichments, sulfur isotopes, and organic biomarker suites have been studied by teams at Woods Hole Oceanographic Institution and Lamont–Doherty Earth Observatory to reconstruct redox stratification, euxinia, and primary productivity linked to contemporaneous events such as the Kellwasser Event and the Late Devonian extinction pulse documented in works from Birkbeck, University of London.
Initial description and naming were part of 19th and early 20th century mapping by geologists from the Ohio Geological Survey and figures associated with the United States Geological Survey; subsequent lithostratigraphic refinement involved contributions by paleontologists and stratigraphers at institutions including Ohio State University, Kentucky Geological Survey, and the Indiana Geological Survey. Debates over subdivision and correlation with equivalent units prompted symposia hosted by the Geological Society of America and publications in journals such as Geology, Palaeogeography, Palaeoclimatology, Palaeoecology, and the Journal of Sedimentary Research, with continuing work by research groups at University of Toronto and McMaster University.
Category:Devonian formations Category:Geologic formations of the United States