Abstract

Saddle dolomite cements are regionally extensive in the Middle Devonian Presqu'ile (or Keg River) barrier and are spatially associated with Mississippi Valley-type mineralization at Pine Point (Northwest Territories). From northeastern British Columbia to Pine Point over a lateral distance of 400 km, these dolomite cements show general trends of decreasing 87Sr/86Sr ratios (0.7106 to 0.7081) and homogenization temperatures (178 to 92 °C), with some increase in δ18O values (-16‰ to -7‰ PDB). These regional trends suggest that hotter and more radiogenic basinal fluids moved eastward updip along the Presqu'ile barrier and mixed with cooler ambient formation waters. These movements of basinal fluids were probably related to tectonic thrusting and compression, sedimentary loading, and tectonic uplift on the western margin of the Western Canada Sedimentary Basin, which began to form during Late Jurassic to Early Cretaceous time and climaxed during the Late Cretaceous to Paleocene. The Middle Devonian Presqu'ile barrier appears to have acted as a deeply buried regional conduit system that played an important role in focusing and channeling these basinal fluids. These regional fluid flows appear to have been responsible for extensive burial dolomitization, secondary migration of hydrocarbons, and local Mississippi Valley-type mineralization in the Western Canada Sedimentary Basin.

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