Stratigraphic Positioning of the Lower Cretaceous Conglomerates, Wind River Basin, Wyoming and Implications for Possible Hydrocarbon Traps

FURER, LLOYD C., Indiana Geological Survey, Bloomington, IN, MICHAEL T. MAY, Indiana University, Bloomington, IN, ERIK P. KVALE, Indiana Geological Survey, Bloomington, IN, and LEE J. SUTTNER, Indiana University, Bloomington, IN

Most previous outcrop and subsurfaces studies of the Lower Cretaceous conglomerates and conglomeratic sandstones in Wyoming have assumed a time equivalency for these deposits. The conglomerates have been utilized to identify the Jurassic-Cretaceous boundary and interpret tectonic conditions within the Sevier foreland basin. However, our integrated subsurface-outcrop correlations show that the conglomerates occur at distinctly different stratigraphic levels, thus invalidating their use in marking the Jurassic-Cretaceous boundary and complicating interpretations of their tectonic significance.

A chert-bearing conglomerate occurs at the base of the Cloverly Formation over the entire western flank of the Wind River basin except within a 30 km Cloverly outcrop belt near Lander. The zero edge of this unit lies just east of Muskrat field where it may be a facies equivalent with what has previously been interpreted as the Upper Jurassic Morrison Formation.

In contrast, in the eastern quarter of the Wind River basin, a thick chert-bearing conglomerate occurs in the upper part of the Cloverly Formation. This conglomerate may be the time-stratigraphic equivalent to the transitional marine "Rusty beds" present in the western margin of the basin. In both areas, the conglomerates and conglomeratic sandstones are encased in thick mudstones.

Paleocurrent data suggest different source areas for the eastern and western conglomerates. The basal conglomerate was derived from the southwest, whereas the younger, eastern conglomerate was derived from the south. Their areal distributions have been useful in suggesting areas of potential structural-stratigraphic hydrocarbon plays.

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)