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Nature of Late Ordovician fluid events in New York: Implications for petroleum generation

Chul Lim

University at Albany (SUNY), Department of Earth and Atmospheric Sciences

Albany, NY 12222

[email protected]

Project goals are documenting origin(s) and veining-model type of Late Ordovician hydrothermal fluids, and origin(s) of the associated hydrocarbons.

Quartz-calcite veins commonly occur in the Ordovician melange along the Taconic orogen-foreland transition zone, in the Capital Region (New York). The veins precipitated at temperatures ranging 230-390° C based on independent pressure correction on homogenization temperatures of aqueous inclusions, which are associated wtih methane inclusions. About 65-100 km to the west, the Cambrian-Ordovician carbonates commonly bear in vugs/fractures oil inclusions and solid petroleum giving bitumen reflectance higher than expected from burial depth. The methane inclusions may be parts of petroleums generated through brief but intense heating of the Ordovician black shales (Utica Shale), by heat transfer from hot advecting fluids, which also contributed to driving the hydrocarbon flows toward the foreland (squeegee model).

Origin(s) of the fluids will be determined by calculation from vein-mineral d18O and precipitation temperatures, and direct extraction measurement of inclusion water, which give d18O and dD (deuterium) of the vein-forming water, respectively, thereby the water type(s). The amount of water-rock interactions, based on d18O of vein quartz and adjacent wall rock, permits definition of the Taconic vein system in terms of established veining models, constraining the fluid-migration scale and open/closed systems. The d13C and dD values of methane can constrain genetic processes (thermal, bacterial, CO2-reduction) thereby, along with fluid inclusion data, leading to test of the hydrothermal heating hypothesis.

This project will improve understanding of hydrothermal events during active faulting and their role in maturation of hydrocarbons.

AAPG Search and Discovery Article #90060©2006 AAPG Foundation Grants-in-Aid