Controls on Late Cretaceous--Paleocene Sedimentation in Wyoming: ABSTRACT

Recent developments in the time-stratigraphic interpretation of seismic record sections have indicated the need for separating tectonic and eustatic processes. The combination of a eustatic rise with a major orogenic episode during the Paleocene in Wyoming resulted in a stratigraphic sequence of economic importance. This sequence was deposited during a period of worldwide onlap, and a period of thrusting and foreland uplift. More than 5,000 ft (1,500 m) of stratigraphic fill of intermontane basins record these processes. Lithologic, environmental, and petrographic observations indicate sea-level changes, strandline positions, paleocurrent patterns, and areas of provenance. Authigenic glauconite suggests an area of brackish to marine transgression within the Cannonball sea. Supporting this observation, specific vertebrae faunas indicate that central Wyoming was inundated by the worldwide post-Danian transgressive onlap. Other environmental criteria support the paleogeographic reconstruction of a broad interior sea invading an area of rising uplifts, encroaching thrust plates, and subsiding basins. These boundary conditions provided the framework for the development of commercial hydrocarbon and coal accumulations. Lacustrine and marine source and reservoir rocks, coastal swamps, and thick subbituminous coals were developed in response to the climatic, tectonic, and eustatic history. These aspects are interpreted from the mineralogy, palynology, petrophysical responses, and the facies patterns in outcrop and subsurface sections. End_of_Article - Last_Page 546------------