Hydrocarbon maturation in thrust belts: Thermal considerations

Sedimentary strata within thrust belts experience transient thermal histories which perturb the maturation paths of organic material contained within the rocks. Calculation of the thermal history, including perturbations which occur with overthrusting, for a particular sequence of tectonic events, allows us to evaluate the timing of maturation reactions and the remaining generative potential in the source rock during the evolution of the geologic terrain. In addition, thermal-maturation indicators can be used to constrain tectonic models for a region and eliminate nonviable geologic interpretations. We have utilized a numerical model to evaluate the thermal response to burial, erosion and thrusting. This model allows us to specify reasonably complex (and geologically reasonable) tectonic histories, including time varying erosion and sedimentation, syn-thrusting erosion, and multiple thrusting events. Such complexities are not easily incorporated in analytic thermal models of thrust belt evolution. In case studies of the western overthrust belt of Wyoming, thermal modeling of geologic histories provides insight into maturation processes, timing and geometries of thrust sheets, and pre-thrusting tectonism. In particular, the timing of thrust sheet motion in the Wyoming portion of the thrust belt appears to be younger than normally thought. Much of the thin skinned thrusting evaluated here appears (from a thermal perspective) to be of similar age to Laramide thrusting in the region.