Abstract: Influence of Source and Processes in Distribution of Heavy Minerals, Muddy Sandstone (Lower Cretaceous), Wind River Basin, Wyoming

Tumkur R. Gopinath, K. Renee Davis, Wayne D. Martin

Heavy-mineral abundance in the Lower Cretaceous Muddy Sandstone, Wind River basin, Wyoming, is controlled by depositional environment and source-area lithology. The minerals common to these rocks include zircon, tourmaline, biotite, garnet, apatite, and rutile. Samples from barrier-bar, lagoon, tidal-flat, estuary, and delta-front deposits were examined for relative abundance of heavy minerals of these environments. Discriminant-function analysis of heavy-mineral abundance and mean-zircon size and standard deviation reveals variation as a function of depositional processes and source-area lithology.

The delta front and associated barrier bar in the northern part of the basin were supplied with sediments rich in biotite and garnet, whereas the tidal flat, estuary, lagoon, and barrier bar in the south were supplied with sediments rich in zircon and tourmaline. In spite of the differences in source, environmental discrimination was possible on the basis of relative abundance of heavy minerals owing to the unique processes in depositional environments.

Tidal-flat and estuarine environments, characterized by similar processes, tend to be enriched in zircon and tourmaline, whereas the associated lagoon contains a large amount of biotite and coarse-grained zircons. Variability in zircon/rutile and apatite/zircon mean sizes distinguishes lower-shore face, middle-shore face, and delta-front rocks which had a common source in the northern part of the basin. It was observed that discrimination of the environments on the basis of source variation is stronger than processes in the depositional environments.

AAPG Search and Discovery Article #90972©1976 AAPG-SEPM Annual Convention and Exhibition, New Orleans, LA