Regional Tectonic Influence on Early Cretaceous Depositional Patterns in Powder River Basin, Wyoming and Montana

J. Gregory Bryan, Timothy J. Petta

Integration of gravity, magnetic, seismic, and subsurface data from the Powder River basin indicates left-lateral wrenching caused principal and secondary shear compression to develop along northwest and east trends, respectively. This well-documented strain fabric caused by Laramide events has affected basin morphology and depositional patterns within the basin since the Early Cretaceous. Regional lineaments mapped at the surface have vertical displacements of tens of feet. These slightly displaced features can be correlated with wrench-related synthetic and antithetic fractures that display miles of subsurface lateral displacement.

Results of detailed integrated forward modeling indicate these fractured zones had a significant effect on the distribution of Lower Cretaceous reservoir sands. Case histories from Buck Draw (Dakota Formation) and Bell Creek (Muddy Sandstone) fields illustrate how the consideration of basement tectonic influence is important to the proper evaluation of exploration leads. Proper use of all available data is essential to the reduction of exploratory risk and can aid in planning offset locations.

AAPG Search and Discovery Article #91030©1988 AAPG Annual Convention, Houston, Texas, 20-23 March 1988.