GEOCHEMICAL AND ISOTOPIC CHARACTERIZATION OF POTENTIAL GAS BEARING UNITS OF THE UTICA AND MARCELLUS SHALE, NEW YORK

Stratigraphically the Flat Creek member of the Ordovician Utica Shale, and the Union Springs member of the Devonian Marcellus Shale are the lowest lying members of their respective formations, and both are of interest due to their unconventional gas producing potential. Both the Flat Creek as well as the Union Springs are overlain by an interbedded shale limestone unit, which is indicative of sea level oscillation. Above the Flat Creek, in stratigraphic succession, lies the Dolgeville followed by the Lower Indian Castle and Upper Indian Castle members (Baird and Brett, 2002). The Cherry Valley member of the Marcellus Shale separates the Union Springs from the Oatka Creek, the unit’s uppermost member. Both formations thicken to the east, and deepen to the south. Major and trace element geochemistry of the Union Springs and Flat Creek members have been determined by ICP-MS from drill cores and cuttings taken from twelve counties located in central and western New York. Samples were collected and analyzed throughout each well, every five to ten feet and significant differences were seen between members of opposing shale groups. In the Flat Creek, major element trends show increasingly high concentrations of CaO (CaO-10.1x) and a minor enrichment in P2O5, while being depleted in SiO2, Al2O3, Fe2O3, MgO, Na2O, K2O, TiO2, MnO, Cr2O3; Union Springs major element averages are more compatible with UCC values with a slight enrichment in Al2O3, and Fe2O3. The Union Springs shows significant enrichment in trace elements (Ag-7.8x; As-5.4x; Cd-38.8x; Cu-3.8x; Mo-71.4x; Sb-5.1x; U-7.9x; V-3.8x; Zn-4.6x); while Flat Creek concentrations are depleted, with noticeable enrichments in only Sr and W (Sr-5.7x; W-6.1x). Total carbon values in the Flat Creek (5.78%-12.54%) are much higher than those in the Union Springs (2.93%-7.79). Ni/Co redox ratios indicate that the Union Springs was likely deposited in anoxic conditions, while the Flat Creek redox indicators tend to be more oxic. These differences are likely related to the higher proportion of carbonate dilutant in the Flat Creek member. Both units are dominated by a Precambrian provenance with Nd model ages ranging from 1913-1988 Ma in the Utica Shale to 1504-1689 Ma in the Marcellus.