Full text loading...
, Paul J. Sylvester1
and Kathryn E. Snell3
Beef calcite veins in the Green River Formation of the Uinta Basin, Utah, were geochemically characterised to test two hypotheses: (1) that beef calcite veins can form during extensional tectonism and (2) that fluid overpressure can develop in open or partially restricted hydrologic systems. Laser ablation U–Pb geochronology yielded three precipitation ages, with the most precise at 24.8 ± 4.8 Ma (2σ), consistent with maximum burial of the formation and coinciding with uplift of the Uinta Basin segment of the Colorado Plateau. Clumped isotope thermometry indicates precipitation temperatures between 55°C and 72°C—substantially lower than the estimated host rock temperatures of 110°C to 140°C based on a ~30°C/km geothermal gradient. δ13C and δ18O values of beef calcite range from 1.6‰ to −1.2‰ and −10.7‰ to −11.5‰ (VPDB), respectively, with calculated δ18O of the precipitating fluid (VSMOW) ranging from −3.3‰ to −5.2‰. These values are consistent with a mixed meteoric and shallow connate water source, suggesting the downward invasion of cold, evolved meteoric fluids along faults and fractures during post‐Laramide extensional tectonic deformation. The overpressure required for beef calcite formation may have been generated by hydraulic head associated with these downward‐migrating fluids and the subsequent lateral displacement of basin brines along stratigraphic interfaces beneath regionally continuous mudstone and evaporite seals.
,Beef calcite veins record paleo‐overpressure in sedimentary basins. In the Green River Formation, U–Pb ages, clumped isotope temperatures and stable isotope signatures suggest that overpressure developed from hydraulic head during the downward migration of mixed meteoric and evolved connate fluids along tectonically generated faults and fractures.
Article metrics loading...
Full text loading...
References
Data & Media loading...