The Upper Ordovician (lower Katian; upper Chatfieldian-lower Edenian) Lexington-Trenton limestone and Point Pleasant-Utica shale intervals are important subsurface stratigraphic units across Ohio as they are the sources of significant conventional and unconventional hydrocarbon resources. However, both units exhibit anomalous distributions across the state and heterogeneous relationships, especially in areas where they intertongue. The limestone units show a peculiar SW-NE thinning trend across Ohio, whereas the overlying shale units show an anomalous thickening along the same trend-a trend associated with the poorly understood Sebree Trough, a supposed Late Ordovician paleobathymetric low related to the coeval Taconic Orogeny. To explore relationships among Lexington-Trenton carbonates, Point Pleasant-Utica shales, and the presumed Sebree Trough, multivariate statistical analysis was used to compare geophysical well logs across the state with well logs referenced to the mineral content of 4 Lexington-Trenton-Point Pleasant-Utica cores. Comparing well-log responses with the mineral content of the reference cores allowed the discernment of 10 electrofacies, keyed to lithofacies in the cores. Software analysis of many other well logs across the state then made electrofacies assignments by comparing well-log responses from the other wells with well-log responses from the reference cores preset into the software. Electrofacies responses were color-coded, mapped in wells at 0.6 m (2 ft) resolution, and used to make section lines and isopach maps of similar electrofacies. Isopach maps and cross sections confirm the presence of the Sebree Trough across Ohio, with trends that parallel existing and projected basement structures. This suggests that the Sebree Trough in Ohio was a bathymetric low, which was, at least in part, controlled by reactivation of basement structures due to far-field Taconic stresses.
|Number of pages||23|
|Journal||Ohio Journal of Science|
|State||Published - 2022|
Bibliographical noteFunding Information:
This research was funded in part by the AAPG Grants-in-Aid Program, the Ohio Geological Society Named Grant, the Case Western Reserve Department of Material Science Student Research Grant, and the Society of Petrophysicists and Well Log Analysts Research Grant. The Ohio Department of Natural Resources, Division of Geological Survey, also supported this work through the use of their core and well-log data as well as guidance during the final writing stages. Special thanks go to Michael Solis for help throughout the research process and for reviewing the article before submission. We also wish to thank the Editor, Dr. Lynn Elfner, and the 8 anonymous reviewers, who helped to substantially improve the paper. The software was generously donated by geoLOGIC systems ltd., and Eric Geoscience. This work is dedicated to the memory of Dr. Eric Eslinger.
© 2022 Bloxson et al.
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