Use of Vitrinite Reflectance Profiles to Determine Timing of Structural Development in Piceance Basin, Western Colorado

Ronald C. Johnson, Vito F. Nuccio

Detailed vitrinite reflectance profiles were constructed for the subsurface and for the uplifts surrounding the Late Cretaceous to Paleogene Piceance basin of western Colorado. The Piceance basin is a typical asymmetrical Laramide basin with gently dipping southern and western flanks and a sharply upturned eastern flank that drapes over a system of thrust or reverse faults at depth. These thrusts commonly underlie anticlines in the southeastern and northern parts of the basin. In the northern part of the basin, surfaces of equal vitrinite reflectance are relatively flat and pass through structures and the sharply upturned eastern flank, indicating that the observed levels of thermal maturity were reached after the end of the Laramide orogeny. In contrast, in the southern art of the basin, surfaces of equal vitrinite reflectance outline or mimic Laramide structures but show less structural relief than the deformed strata, indicating that thermal maturity trends date largely from the Laramide orogeny. These results are the opposite of what was expected because the southern part of the basin was affected by Oligocene plutonism and Miocene through recent basaltic extrusive events, whereas no known Tertiary magmatic activity occurred in the northern half of the basin. A likely explanation is that there was post-Laramide movement on some of the structures in the southern part of the basin, possibly associated with salt diapirism. Time-temperature modeling was used to generate other explanations for these results.

AAPG Search and Discovery Article #91022©1989 AAPG Annual Convention, April 23-26, 1989, San Antonio, Texas.