CHARACTERIZATION OF DEVONIAN BLACK SHALE DEPOSITIONAL ENVIRONMENTS AND CATAGENETIC PROCESSES USING NITROGEN ISOTOPES AND OTHER GEOCHEMICAL PROXIES: OHIO SHALE, EASTERN KENTUCKY

Characterizing the depositional environment of organic-rich black shales has long been an interest in regards to evaluating potential hydrocarbon content. The Ohio Shale has been classified as a black marine shale, but previous research has proven that the Ohio is lithologically heterogeneous within individual members. Therefore, a more complete geochemical analysis should be conducted in order to fully understand the depositional conditions individual members of the Ohio Shale were deposited in and their subsequent effects during catagenesis.

Bulk nitrogen isotopes (δ¹⁵N_bulk) values have been frequently used to evaluate paleoredox conditions of depositional environments, alterations that occur during the sinking of particulate organic matter through the water column, and early burial diagenesis within a few meters of the water-sediment interface; however, previous Ohio Shale depositional environment interpretations have neglected to utilize nitrogen isotopes as a complementary proxy. Other research investigating catagenetic alterations of δ¹⁵N_bulk values in Devonian shales have shown little correlations between isotopic modification and thermal maturation. Although the degree of modification from fluid flow on δ¹⁵N_bulk remains elusive, separating nitrogen into its inorganic species can provide a useful proxy with respect to fluid flow and compartmentalization within an unconventional system.

The goal of this research is to utilize bulk and inorganic nitrogen isotopes to characterize the depositional conditions and catagenetic processes that occur within the Ohio Shale. The objectives include: 1) measuring δ¹⁵N_bulk, δ¹⁵N_inorganic, δ¹³C_organic, and weight percent of total nitrogen (TN), inorganic nitrogen (IN), and total organic carbon (TOC), 2) conducting petrographical analyses to provide insight of overall lithological compositions and clays present, and 3) propose an overall syn, and post-depositional model that characterizes the alteration δ¹⁵N_bulk due to fluid migration. The results will enhance our understanding of individual Ohio Shale member deposition, and the catagenetic alterations of inorganic nitrogen species during temperature regimes responsible for hydrocarbon generation.