DEPOSITIONAL PROCESSES AND XRF GEOCHEMISTRY OF THE UTICA SHALE WITHIN THE ORDOVICIAN OUTCROP BELT IN CENTRAL NEW YORK STATE

This study combines detailed sedimentological descriptions with pXRF-based elemental abundance measurements of the Trenton Group and Utica Shale in Central New York. The primary data set was derived from drill cores collected by NL Industries in mid-1970’s, and currently curated by the New York State Museum in Albany, NY. These unweathered cores represent an unprecedented opportunity to study the detailed sedimentology, stratigraphy, and geochemistry of these economically significant units. Far from a monotonous interval of mudstone, the Utica Shale in Central New York reflects deposition in a dynamic marine environment that at times was shallow enough to allow for wave and current reworking of sediment, as well as mixing of oxygenated surface waters with more anoxic bottom waters. Other lithofacies represent transport by turbidity currents and debris flows; in addition to low energy suspension settling of mud.

By annotating each sample with a lithofacies designation, vertical and lateral trends within one rock type can be investigated. For example, black fine mudstone can be isolated from thin interbedded carbonate-rich turbidite and debris flow units to track compositional changes in the detrital fraction of the background sediments. Calcium concentrations of these mudstones are higher in the Flat Creek Shale, the lower portion of the Utica Shale, than the overlying Indian Castle Shale, and decrease westward towards the craton within the Indian Castle Shale. The ratios of detrital proxies relative to Al highlight previously unidentified changes in the bulk composition of siliciclastic detritus across two disconformities within the Indian Castle Shale. This likely relates to variation in the relative contribution of sediment derived from the cratonic interior, eroded carbonate shelf, and rising orogenic wedge, as well as possible exhumation of the Adirondack Massif. The concentrations of redox sensitive proxies increase upwards throughout the Utica Shale and towards the basin center. The broad results of this study are consistent with previous interpretations, indicating that high resolution lithologic descriptions and XRF-based elemental concentration data may reveal more cryptic changes in sediment provenance and bottom-water redox conditions within the Taconic foreland basin.