A COMPREHENSIVE LOOK AT THE LATE ORDOVICIAN (KATIAN) UPPER LEXINGTON EQUIVALENTS OF EASTERN OHIO: DIFFERENTIATING THE UTICA – PT. PLEASANT SYSTEM

The “Utica Formation” and “Point Pleasant" (mixed shale and thin limestones) of driller’s terminology is a major target for unconventional oil and gas development in eastern Ohio, and is the largest producing unit in the state of Ohio. Despite major production yields from this unit, the paleoenvironmental interpretations, stratigraphic nomenclature, and litho-, chemo-, and sequence stratigraphic framework of this region remains poorly understood. Here, we present a detailed analysis of a single drillcore from Cadiz, Ohio, using an integrative chronostratigraphic approach to tie the sequences of this Point Pleasant basin section to those of the shallow-water Lexington Platform and to develop a paleoenvironmental interpretation of this distal section. We analyzed the 100-m-thick Cadiz core for major and trace-element concentrations (XRF), total organic carbon (TOC%), and carbonate carbon isotopes at a high stratigraphic resolution (~50 cm intervals). Environmental fluctuations were interpreted on the basis of widely used geochemical proxies, developed from modern and ancient marine systems. These results, set within a framework of biostratigraphy and faunal epiboles, suggest that distal expressions of the Lexington Formation are recognizable despite the absence of major well-differentiated sequences. We infer that the “Utica Formation” of eastern Ohio is a more distal expression of the Bromley Member through Kope Formation of the well-differentiated Lexington Platform. 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 deviation of C_org:P ratios in these dark shales from modified Redfield ratios indicate suboxic to anoxic benthic conditions in this interval but not in the overlying Utica.