Lithofacies Distribution of the Middle to Upper Devonian Ohio Shale in the Southern Appalachian Basin, Kentucky
The Devonian Ohio shale, consists of interbedded black, dark gray, gray and brownish gray organic rich mudstones that were deposited east of the Cincinnati Arch in the Appalachian Foreland Basin. The Ohio Shale of Southern Appalachian Basin in Kentucky has been divided into Huron Member, Three Lick Bed and the Cleveland Member. In the west-central part of Kentucky close to the Cincinnati Arch a heterolithic interval of Middle Devonian (Givetian) shales, sandstones and carbonate occurs at the base of the Devonian black shale succession. Based on lithology and sedimentary structures from three complete cores, seven lithofacies have been identified: black silty mudstone, pale gray silty mudstone, interbedded dark and pale gray silty mudstone, black silty mudstone with pyritic enrichment, black dolomitic mudstone, strongly bioturbated black silty mudstone and black silty mudstone with mm to sub-mm scale laminae. Each of these lithofacies represent a particular environment of deposition that had formed in response to sea level fluctuation and sediment input. Lag deposits and sharp erosional contacts are seen in cores and they mark gaps in the sediment record. The lower part of the Ohio Shale in the west-central part of Kentucky is made of a few coarsening up cycles (4.5 meters thick) that contains smaller scale coarsening up cycles within them. Geophysical wire-line logs and cores show an overall westward thinning trend in the rocks of the Ohio Shale. Wire-line logs have also been used in conjunction with cores in the identification of coarsening up, fining up trends as well as maximum flooding surfaces and system tracts. Based on geophysical logs and cores, five sequences and eleven system tracts have been identified. This detailed sedimentological work that integrates core, outcrop and geophysical logs will aid in establishing a comprehensive east-west trending sequence stratigraphical section for the Ohio Shale in the Southern Appalachian Basin in Kentucky. It will also enhance our understanding of the changing depositional environments where these rocks were deposited.
AAPG Datapages/Search and Discovery Article #90291 ©2017 AAPG Annual Convention and Exhibition, Houston, Texas, April 2-5, 2017