Depositional Environment and Sedimentary Facies of the Proximal Middle Devonian (Givetian) Geneseo Formation of New York, USA

Wilson, Ryan D.; Schieber, Juergen

Shale and mudstone facies of the Middle Devonian Geneseo Formation have been characterized and interpreted with regard to depositional setting in the proximal realm of the Catskill delta. At time of deposition the Acadian uplift supplied detritus from the east and fueled delta expansion. Autogenic processes, coupled with a general rise in sea-level, appear to have exerted significant control on the distribution of mudstone facies. This study we combine high-resolution facies analysis and geochemical evaluation of outcrop and core samples to better understand depositional environment and facies distribution in proximal areas of the Geneseo Formation.

In central New York, the Geneseo Formation consists of dark gray, pyritic and banded black shales, homogenized gray mudstones, and gray silty mudstones/muddy siltstones with intercalated concretionary carbonate horizons. Variations in δ¹³Corg appear to reflect shoreline proximity, which can be used to infer depositional environment. Carbon isotope values of organic-matter reflect mixing of a terrestrial component with δ¹³C values of about -26.5‰, and a marine component of about -29.5‰. Typically, heavier δ¹³C values are associated with elevated Ti/Al and Si/Al ratios, decreased FeT/Al, and lower trace-metal concentrations in more organic-lean, moderately to strongly bioturbated gray mudstones. Lighter isotopic values are typically associated with decreased Ti/Al and Si/Al ratios, increased FeT/Al, and trace-metal enrichment in organic-rich, sparsely to weakly bioturbated pyritic and banded black shales.

The Geneseo Formation exhibits several shallowing upwards cycles (parasequences) that can be identified on the basis of sedimentary features, elemental ratios, trace metal concentration (i.e., V, Ni, Zn, Cu, Cr), as well as the carbon isotope record. Heavier isotopic values reflect shallower water conditions and higher accumulation rates, under dysoxic to oxic water-column conditions. This is confirmed with the decreased trace-metal concentrations, and elevated Ti/Al and Si/Al ratios, suggesting basinward migration of the paleoshoreline. Lighter isotopic values and enrichment of trace-metals suggest deeper water conditions and lower accumulation rates, under sub-oxic to dysoxic water-column conditions.

AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013