Marine paleoecology of the Eads Mill Member, Hinton Formation, Upper Mississippian, West Virginia and Virginia.

摘要

During the Late Mississippian, the Eads Mill Member of the upper Hinton Formation was formed during the last marine transgression before deposition of the Princeton Sandstone. Five outcrops extending northward from southwest Virginia into southern West Virginia were sampled, and constituent fossil genera were identified in the lab. Seven guilds were recognized and similar taxa were grouped together based on their morphology and life habits. Binary presence/absence data were compiled for all guilds at each sampled unit, and processed using four multivariate techniques in order to identify any underlying paleoecological signal. All techniques yielded a strong trend in the data interpreted to represent the salinity tolerances of the taxa within each guild, though other environmental factors such as substrate and turbidity could also have had a minor influence. Lithologic data and multivariate analyses were then combined to understand the changing environmental conditions during the formation of the Eads Mill Member. Both sets of data indicate that the Eads Mill Member was formed by an overall transgressive/regressive cycle that formed brackish and transitional marine conditions at the base and top of the member, and open marine conditions in the middle represented by two laterally continuous fossiliferous limestones. Multivariate results were compared to those of the underlying Fivemile Member, whose taxa indicated that it was deposited in predominantly brackish marine conditions. These two members were then related to similar taxonomic compositions in the older Bluefield Formation, the Greenbrier Limestone Group, and the Avis Limestone. The results indicate that water salinity and corresponding taxonomic salinity tolerances were the controlling factors on taxonomic diversity of marine units formed in the Appalachian Basin during the Late Mississipian.