Abstract: Comparison of Vitrinite Reflectance Models: Examples from the Late Cretaceous Mesaverde Formation, Wind River Basin, Wyoming

Bonnie L. Crysdale, C. E. Barker

Reconstruction of the post-Early Cretaceous burial history of the Wind River Basin indicates almost continuous deposition in the basin trough from the Late Cretaceous to the end of the Laramide orogeny in the early Eocene. Upper Cretaceous Mesaverde strata in the basin trough reach a depth of 18,500 ft, a present temperature of more than 200°C, and mean random vitrinite reflectance (R_v-r) of more than 2.0%. In contrast, the Mesaverde Formation along the southwestern margin of the basin records several cycles of deposition and erosion and has reached only 80°C and 0.5% R_v-r. Peak temperature (T_peak) in the basin was reached during maximum burial in Oligocene to Miocene time, and most of the basin has now cooled by 10-20°C due to regional plift beginning about 10 Ma.

Cyclical deposition of the Mesaverde Formation on the basin margin versus continuous deposition in the basin trough allows different vitrinite reflectance evolution models to he compared by tracking one rock unit through a wide range of temperatures and burial conditions. A limited-heating-duration vitrinite reflectance geothermometer model, based on T_peak and an R_v-r data set from Barker and Pawlewicz (1993), was compared to the unlimited-heating-duration LLNL kinetic model. Burial temperature was assessed by varying heat flow until peak paleotemperature matched the prediction from fluid inclusions or from the vitrinite reflectance geothermometer. These comparisons suggest close agreement between predicted and observed vitrinite reflectance and peak temperature. The LLNL kinetic model implies vitrinite reflectance evolution ceases within 10 m.y. after T_peak is reached in wells where temperature remains near maximum during the peak burial phase. Both models indicate that the continuing effects of vitrinite reflectance reactions are restricted soon after T_peak is reached.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994