Revised Tertiary Stratigraphy and Paleontology of the Western Beaver Divide, Fremont County, Wyoming

Abstract

In the western Beaver Divide area in west-central Wyoming, a lens of coarse Tertiary volcanic conglomerate and tuff disconformably overlies Uintan rocks of the Wagon Bed Formation. The coarse volcaniclastic rocks were previously regarded as a facies of the Beaver Divide Conglomerate Member of the Chadronian White River Formation, although fossil mammals from the volcaniclastic unit are species known otherwise only from Uintan rocks. Reexamination of field relations has shown that the White River Formation disconformably overlies the volcaniclastic unit. The “lower Uinta C” temporal equivalence indicated by the fossils from the volcaniclastic unit is no longer anomalous; the underlying Wagon Bed Formation has fossil mammals indicating “Uinta B” equivalence, and the overlying White River Formation has a fairly diverse Chadronian fauna. The Uintan volcaniclastic unit is assigned to the Wiggins Formation. The Beaver Divide Conglomerate Member is restricted to conglomerate in the lower part of the White River Formation. It is composed predominantly of clasts of locally derived Precambrian crystalline rocks.