GEOCHEMICAL VARIATIONS IN BLACK SHALES OF NEW YORK STATE

Several black shale formations, ranging from Ordovician to Devonian in age, outcrop in New York State. Although unconventional gas extraction is not currently permitted in NY, these formations may represent a future resource. Variations in major and trace elements, and organic matter, may lead to a better understanding of depositional environments, target certain areas for future gas potential and identify possible environmental issues with drill cuttings such as radionuclide concentrations. Eight samples from the Marcellus Shale were obtained from outcrops and quarries that span an east to west band in New York. As a reference, other black shale samples were also obtained from the Utica, Skaneateles, Maplewood, Hanover, Deepkill, and Geneseo formations. Whole rock analysis for major and trace elements and organic matter were determined for each sample. All samples showed negative Ce anomalies, indicating that anoxic conditions were present during deposition. These values, however, show no correlation with spatial distribution across the state. A correlation between organic matter and Ni, another indicator of anoxic conditions, is present, with an r² of 0.97 which is supported by Lewan, M. D., & Maynard, J. B. (1982). This indicates algae as the probable source of the organic matter. While the Marcellus Shale is known for its high concentrations of Th and U, concentrations are highly variable. Concentrations of Th range from 1.8 to 12.1 (mg/kg), and U values range from BDL to 68.3 (mg/kg). These lower values could suggest that toxic trace metal concentrations may not be as high as previously thought in all portions of the formation in New York, making it more accessible for natural gas extraction. Organic Matter content values range from 2.43 to 17.48 (wt%) as determined by loss on ignition, however, no clear trend could be observed related to distribution across the state. Overall, the Marcellus Shale appears to be highly variable, and further analysis, including 3D stratigraphic controls, are needed to fully understand the deposition environment and distribution of trace elements and organic content across New York State.