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Sedimentology and XRF-Based Elemental Geochemistry of Cores From the Trenton Group and Utica Shale Along the Ordovician Outcrop Belt in Central New York

Abstract

Drill cores collected by NL Industries in the 1970's along the outcrop belt of the Trenton Group and Utica Shale in Central New York represent an unprecedented opportunity to study the detailed sedimentology, stratigraphy, and geochemistry of these economically significant units. In particular, the Utica Shale accounts for 30% of the undiscovered, technically recoverable shale gas resource potential of the Appalachian Basin, as estimated by the USGS. This study combines detailed sedimentological description with elemental abundance measurements using a Bruker Tracer III pXRF spectrometer. By annotating each sample with a lithofacies designation, vertical and lateral trends within one rock type can be investigated. For example, dark gray mudstones, representing the background deposition in the deep basin, can be isolated from thin interbedded carbonate-rich turbidite and debris flow units to track compositional changes in the detrital fraction related to variability in sediment provenance and tectonic evolution of the basin. This technique has highlighted provenance changes between the Trenton Group and Utica Shale, as well as within the Utica Shale. Similarly, redox sensitive proxies such as U, Mo, V, Mn, Ni, and Cu can be placed within a depositional context to investigate long-term change, rather than local variability related to deposition of individual event beds. The geochemical data produced in this study can be used to generate synthetic total gamma ray logs for comparison to traditional gamma ray logs from nearby wells. This correlation shows how detailed geochemical analyses can be used to upscale low fidelity geophysical and geochemical logs measured in oil and gas wells. The high frequency sedimentological and geochemical variability documented in this study provides valuable insights into the tectonic evolution and paleo-oceanographic history of this basin, and the resource potential of the Utica Shale that common well logs cannot resolve.