Hydrocarbon Maturation in Laramide Basins--Constraints from Evolution of Northern Big Horn Basin, Wyoming and Montana: ABSTRACT

Abstract

Thermal and mechanical models were used to quantify the effects of Laramide uplifts and subsequent synorogenic deposition on the hydrocarbon maturation of Cretaceous source rocks in the Big Horn basin. Laramide deformation and resultant sedimentation has clearly affected hydrocarbon maturation of Cretaceous source rocks (Thermopolis, Mowry, Frontier, Cody). Modified Lopatin-type reconstructions suggest that a significant region containing Cretaceous source rocks has been within the liquid hydrocarbon window. The earliest onset of hydrocarbon maturation in the northern Big Horn basin was latest Eocene, with some regions still containing immature Cretaceous source rocks as a consequence of Cenozoic erosion, uplift of the Pryor Mountains, and lack of burial. Regional geologic features indicate that the basin formed as a result of flexural compensation of an elastic lithosphere during emplacement of the Beartooth and Pryor Mountains, and possibly the Absaroka volcanics. This was determined by 2-dimensional models which predict sediment thicknesses caused by tectonic loading and subsequent sedimentation. Flexural rigidities of 1021-1022 newton-meters adequately explain flexural subsidence in the northern Big Horn basin. The present basin configuration also was compared with a theoretical profile based on geologic constraints. Subsidence models for the present basin profile suggest that Paleocene thrusting of the Beartooth block contributes a majority of the tectonic loading and that Cenozoic erosion has drastically affected the resultant sedimentary sequence (Fort Union and Wasatch). These models, along with stratigraphic reconstructions, can be combined to pinpoint areas of potential hydrocarbon maturation within Laramide-type basins. End_of_Article - Last_Page 482------------