Characterization of the Late Famennian lower Huron Shale Member of the Ohio Shale, southern Scioto County, Ohio
A potential target for future unconventional hydrocarbon exploration including enhanced recovery of natural gas through CO2 sequestration, the lower Huron Shale Member of the Ohio Shale (“lower Huron”) is one of the most regionally extensive Devonian mudrocks in the Appalachian Basin. Understanding the paleodepositional conditions that aided in the preservation of organic matter in this unit is critical for assessing its viability as a potential hydrocarbon play. Multiple analyses were conducted on representative lithologies at a sampling frequency (n=16) of approximately every 2.4 m (7.8 ft) from a core located in Green Township, Scioto County. Measurements include a high-resolution spectral gamma core scan of the entire lower Huron interval, and transmitted and reflected light and SEM imagery of thin sections. δ13C values of the organic carbon and TOC measurements were taken on core subsamples (n=13), while powdered sample splits were utilized to determine average mineral wt% (via XRD) and major and minor trace elements (via XRF/ICP-MS), specifically redox-sensitive trace metals. Mercury intrusion capillary pressure porosimetry was also used to determine porosity from whole-rock core fragments (n=7). δ13Corganic values average -29.9 ± 1.13 indicating a distal marine facies, dominated by organic-rich laminated shale, and comprised predominantly of quartz, illite, mica, and significant amounts of preserved algal material. TOC and porosity average 6.7 ± 1.25 and 2.7 ± 0.69 percent, respectively, across the 38 m (124 ft) lower Huron interval. Chemostratigraphy of trace-element redox proxies (V/V+Ni, V/Cr, Ni/Co) suggest sediment accumulation occurred under a range of oxic to dysoxic and even euxinic conditions, across several mineralogically distinct lithotypes. Furthermore, significant trends in the relative degree of anoxia are positively correlated to existing published data acquired from equivalent strata located 80 km (50 mi) from the studied core. Although fluctuations in terrigenous clastic input, as measured with XRD, and the presence of fault-bounded subbasins associated with the Rome trough appear to have had some influence, periods of high productivity and subsequent O2 depletion are inferred to be a primary contributing factor in the accumulation and preservation of organic matter.
AAPG Datapages/Search and Discovery Article #90373 © 2019 AAPG Eastern Section Meeting, Energy from the Heartland, Columbus, Ohio, October 12-16, 2019