CARBONATE CLUMPED ISOTOPE THERMOMETRY AS A TOOL TO CONSTRAIN THERMAL CONDITIONS IN THE SHALLOW CRUST DURING DEFORMATION AND DIAGENESIS, PARADOX BASIN, UTAH

Quantifying the temperature conditions under which deformation and fluid flow modulate hydrocarbon maturation, porosity, and permeability is important for predicting hydrocarbon formation and preservation in tectonically active basins. Clumped isotope thermometry determines the precipitation temperature of carbonate minerals based on the abundance of ¹³C-¹⁸O bonds in the carbonate crystal lattice, potentially enabling the thermal conditions of fracturing, fluid flow, and growth of diagenetic minerals in hydrocarbon reservoirs to be determined independent of the composition of co-existing fluids, pressure, or time. In order to evaluate the utility of this geothermometer in structural diagenesis studies, we examine the growth conditions of diagenetic calcite cements associated with fault systems in a well-studied carbonate reservoir, the Paradox Basin, Utah.

The Paradox Basin, an intraforeland flexural basin in SE Utah, hosts 3 km of Pennsylvanian-Jurassic sediments that underwent burial, diagenesis and exhumation in the last 120 Myr. We targeted calcite veins developed along sections of the Lisbon Valley and Moab Faults, two major Laramide normal fault systems in the Basin. Previously published vitrinite reflectance, Rock-Eval pyrolysis, fluid inclusion, and stable isotope data indicate that diagenetic calcite veins formed during fault-parallel hydrocarbon migration at 60 – 125ºC. Neither cathodoluminescence nor petrographic analyses of core and outcrop samples indicate fluid composition varied during calcite growth, suggesting basinal fluids migrated along normal faults rapidly. Clumped isotope analysis of these veins will test the hypothesis that diagenetic calcite crystallized coevally with Pennsylvanian-sourced hydrocarbon migration between 60-125° as fluids migrated through the basin from depth, along fault conduits created during Laramide deformation. We evaluate the utility of clumped isotopes to determine fluid migration temperatures, and thermal conditions in the crust during deformation. This study serves as a model for how clumped isotope thermometry can be combined with structural geology of basins to constrain the thermal and chemical history of fluids in tectonically active reservoirs.