Late Ordovician (Katian) Upper Lexington-Kope Equivalents in the Point Pleasant Basin of Eastern Ohio: Correlation and Paleonenvironments of the Utica Point Pleasant System

Abstract

The “Point Pleasant” (mixed calcareous shale and thin limestones) and “Utica” (black shales) form a major target for unconventional oil and gas development, and the largest producing unit, in the state of Ohio. Despite major production, the paleoenvironmental interpretations, stratigraphic nomenclature, and the litho-, chemo-, bio- and sequence stratigraphic framework of these units in the Ohio subsurface remains poorly understood. Here we present detailed analyses of a core from Cadiz, OH, using an integrative stratigraphic approach to tie the sequences of this Point Pleasant basin section to those of the shallow water facies of the Lexington Platform of Kentucky and suggest a paleoenvironmental interpretation of this distal section. High-resolution data on X-ray florescence (XRF), total organic carbon (TOC%), and carbonate carbon isotopes, were obtained throughout the entire profile of the core. These results, set within a framework of biostratigraphy and faunal epiboles, suggest that distal expressions of several divisions of the Lexington Formation are recognizable despite the absence of well-differentiated sequences. The “Point Pleasant” Formation of the subsurface is lithologically unlike that of the type area, and correlates with a middle portion of the Lexington Formation below the true Point Pleasant. “Utica Formation” of eastern Ohio is a distal expression of the Bromley and upper (“River Quarry”) members of the Point Pleasant and Kope Formation of the Lexington Platform. Fluctuations in organic matter concentrations, and redox conditions are interpreted using geochemical proxies developed from modern and ancient marine systems, The highest TOC% zone occurs below the “Utica Formation” in the so-called “Point Pleasant Formation”, the shalier regional expression of the middle/upper Lexington Formation approximately equivalent to the Brannon Member. Strong deviations of C/P values from modified Redfield ratios, in these dark shales, indicate fluctuating suboxic to anoxic benthic conditions in this interval but, surprisingly, not in the overlying Utica.

AAPG Datapages/Search and Discovery Article #90258 © 2016 AAPG Eastern Section Meeting, Lexington, Kentucky, September 25-27, 2016