The origin and timing of late-stage carbonate cements in Devonian carbonates of the deep Alberta basin : based on fluid inclusion and isotopic evidence

Deep basin Leduc Obed and Swan Hills Simonette calcite fluid inclusions yielded Th ranges of 127 to 172°C and 122 to 158°C; while saddle dolomites have Th from 136 to 148°C and 133 to 162°C, respectively. Calcite data from the subsurface suggest a 20°C/km geothermal gradient and saddle dolomite data a gradient around 23°C. Vug-filling calcites from Spray Lakes, Parker's Ridge and Big Hill, yielded Th data (128.0 to 155.1°C) similar to vug-filling cements from Obed and Simonette. Fluids in the fracture-filling saddle dolomites analysed have an average T h of 171.6°C and salinity of 17.1. Post-thrusting fractures yielded calcites with the lowest Th and salinity suggesting precipitation from cooler, largely meteoric waters. Homogenization temperature data for vug and fracture-filling from subsurface and outcrops suggest that late calcite and dolomite phases were precipitated near maximum burial, in the Paleocene.Many of the Obed and Simonette late-stage calcites and dolomites have very high 87Sr/86Sr signatures (up to 0.7370). Obed late calcites show a strong east to west increasing trend in Sr isotopes across the buildup---suggesting fault control of this margin. (Abstract shortened by UMI.