Abstract

The distribution of coal and evaporites, the nature of associated plant fossils, and a comparison of detrital mineralogy indicate both geographic and temporal variations in Permo-Pennsylvanian paleoclimate in the Ancestral Rockies. The distribution of coal and evaporites suggests that the eastern block of the Ancestral Rockies may have experienced a climate which was more humid than occurred along the western block in the Early Pennsylvanian. A higher relative percentage of detrital monocrystalline and polycrystalline quartz and less total rock fragments in the Fountain Formation with respect to the Cutter Formation also supports this climatic difference. Paleobotanical data also are consistent with this model but are not conclusive by themselves. This climatic interpretation is consistent with a near equatorial position of the Ancestral Rockies adjacent to an epeiric sea. By Permian time ubiquitous evaporites suggest a regional shift toward more arid conditions throughout the Ancestral Rockies.