2015 GSA Annual Meeting in Baltimore, Maryland, USA (1-4 November 2015)

Paper No. 28-24
Presentation Time: 9:00 AM-5:30 PM


MARTINEZ, Aaron M.1, BOYER, Diana L.2, LOVE, Gordon D.1 and DROSER, Mary L.1, (1)Department of Earth Sciences, University of California, Riverside, 900 University Ave, Riverside, CA 92521, (2)Department of Earth Sciences, SUNY Oswego, Oswego, NY 13126, amart109@ucr.edu

The Cleveland Shale member of the Ohio Shale, cropping out in eastern Ohio, is a black shale associated with the final biotic turnover of the Late Devonian extinction events. This unit records a period of deep water deposition within the Appalachian Basin and is exposed as a nearly homogeneous black shale interval ranging from one meter to over 30 meters in thickness. This study utilizes a multiple proxy approach, encompassing both geochemical and paleontological methods, to decipher the paleo-redox and biotic history throughout the Cleveland Shale.

Preliminary data from two Cleveland Shale localities (Big Creek, near Cleveland, Ohio; Rocky Branch, near Gahanna, Ohio) exhibit complex signals. Trace fossil data, collected as ichnofabric index (a metric of relative amount of bioturbation), show a variable array of fully oxygenated, dysoxic, and anoxic bottom waters. Trace metal data (including Mo, V, Ni, and U) also demonstrate variation but reveal episodes of euxinia (sulfidic waters). Rock-Eval pyrolysis indicates that the Cleveland Shale has experienced a mild thermal history and is in prime condition for lipid biomarker analysis. Biomarkers, in turn, detail the past microbial community structure, and we have detected abundant isorenieratane, a tracer for photic zone euxinia, in strata of the upper Cleveland Shale. Combined, these proxies reveal sections of dysoxic through euxinic conditions, indicating fluctuating marine redox during the deposition of the Cleveland Shale. This interval is significant as it preserves a record of the Late Fammenian Hangenberg Bioevent, which represents the final pulse of the End Devonian mass extinction. These results lay the foundation for understanding the paleoenvironmental and biotic setting during the Hangenberg Bioevent within the Appalachian Basin.