STABLE ISOTOPE AND FLUID INCLUSION CONSTRAINTS ON THE BURIAL HISTORY OF THE UTICA FORMATION, NEW YORK STATE

Thermal maturation and burial history of the Utica Formation and coeval platform facies of the Trenton Group are recorded in widespread carbonate veins. Stable isotope and fluid inclusion data document temporal and geographic variation in fluid composition and burial temperature across the central New York outcrop belt. Near the Taconic structural front, overmature Utica Formation hosts calcite veins with lo-salinity (<4% NaCl equiv.) fluid inclusions derived from shale dewatering with T_h >160^oC. Fluidized sand-dikes formed contemporaneously with calcite veins. In the central Mohawk Valley, 80 km west of the structural front, relatively lower thermal maturity is recorded in calcite veins containing aromatics and C₂-C₃ hydrocarbons, and fluid inclusions with T_h <140^oC. Slightly higher fluid inclusion temperatures (T_h >140^oC) occur in the western Mohawk Valley. Low-salinity fluid inclusions are generally characteristic of Utica veins across the outcrop belt, and contrast with high-salinity (>15% NaCl equiv.) fluid inclusions in lower Paleozoic and basement-hosted veins of the Adirondack region.

Oxygen and carbon stable isotope data from a wide array of vein systems in the Mohawk Valley generally support derivation of fluids from mud dewatering, with most fluids forming in equilibrium with host sediment at burial temperatures consistent with fluid inclusion data. Late carbonate veins in the eastern Mohawk Valley outcrop belt have unusual positive carbon isotope signatures (δ¹³C = +8 to +14) indicating contribution of carbonate from residual hydrocarbon degradation. Horizontal calcite veins are present across the outcrop belt, are sometimes associated with minor folds and likely formed during episodic high fluid pressure events. Stable isotope signatures suggest that horizontal veins formed at somewhat lower temperatures than later vertical veins within the same outcrop (horizontal veins at one locality have δ¹⁸O_PDB of -7 to -9; vertical veins have δ¹⁸O_PDB  of -8 to -12).