PALEOENVIRONMENTAL PROXIES AND DEPOSITIONAL ENVIRONMENT OF THE LOWER UTICA SHALE (UPPER ORDOVICIAN) IN CORES 74NY10 & 75NY2 CENTRAL MOHAWK VALLEY, NY

The Mohawk Valley is located in central New York within the Taconic Foredeep, which was the site of active faulting and crustal subsidence during the Middle and Late Ordovician. The purpose of this study is to examine the lithology, geochemistry, and total organic carbon (TOC) within the stratigraphic interval in the Flat Creek Member of the Utica Shale that is occupied by the Corynoides americanus graptolite biozone in core 74NY10 (near Gloversville) and other well-studied sections in the region (especially Core 75NY2, near Balston Spa). We collected samples every 6 cm from 74NY10 and each sample was analyzed for elemental composition using the NITON XL3t GOLDD handheld EDXRF (energy dispersive X-ray fluorescence) by Dr. Gary Lash, SUNY-Fredonia.

Elemental composition data showed three distinct units through the studied section of core 74NY10, denoted as Unit 1, from the Trenton/Utica contact to 312 cm above the contact, Unit 2, 312 cm to 1502 cm above the contact (coincident with the base of the C. americanus Zone), and Unit 3, 1502 cm above the contact through the rest of the studied section. The base of the O. ruedemanni Zone probably corresponds to a level at about 1812 cm above the base of the Utica Shale in 74NY-10, within the lower part of Unit 3. The Utica Shale of the studied section is 77% CaCO₃, much of which reflects passive precipitation of diagenetic carbonate in void spaces of the host sediment prior to compaction. The gradational change between the Trenton and the Utica Shale coupled with similarities in the elemental data suggests the Trenton shares the same source material as Unit 1 and Unit 3 of the Utica Shale; whereas, Unit 2 of 74NY10 appears to have a different sediment source (possibly the Taconic hinterland) that has the same elemental composition trend as Units 2 and 3 in 75NY2, suggesting a deeper depositional setting than in Units 1 and 3. The water column redox of Units 1 and 3 in 74NY10 appears to be dominantly anoxic to dysoxic based on V/(V+Ni) and Mo abundance, however U is highly depleted relative to expectations, similar to relationships seen in previous work on core 75NY2. Elevated concentrations of Cu, Ni, Ba, Fe and S in these same sediments suggest anoxia was driven by surface productivity and basin restriction.