PALEOENVIRONMENTAL INFERENCES BASED ON FOSSILS AND LITHOLOGY OF OUTCROPS OF THE PENNSYLVANIAN BRUSH CREEK MARINE ZONE OF THE GLENSHAW FORMATION (CONEMAUGH GROUP), BURNING SPRINGS ANTICLINE, PLEASANTS COUNTY, WEST VIRGINIA

The Upper Pennsylvanian Brush Creek marine zone of the Glenshaw Formation outcrops on the northern plunging nose of the Burning Springs Anticline along Sled Run in Pleasants County, West Virginia. The Brush Creek marine zone here represents a relatively rapid transgressive-regressive cyclothemic sequence deposited as the Midcontinent Sea transgressed from the southwest across this region, then regressed, due to glacial-eustatic sea level fluctuations.

The Brush Creek Coal is 0.58 m thick, followed upward by 1.14 m of nonfossiliferous, thinly fissile, black shale. Above this, the sequence of lithofacies represented by the Brush Creek marine zone (from older to younger) consists of 0.12 m of very fossiliferous, black to dark gray, rubbly-bedded mudstone; approximately 0.20 m of very fossiliferous, black to dark gray, rubbly-bedded limestone (primarily wackestone to grainstone); 0.076 m of very fossiliferous, black to dark gray, rubbly-bedded mudstone; and about 3.0 m of sparsely fossiliferous, thinly fissile, dark gray shale.

The Brush Creek limestone and mudstones are very fossiliferous, but are dominated by mollusks, mostly shallow burrowing and epifaunal bivalves along with gastropods (including abundant microgastropods). The limestone also contains a few horn corals and coiled and straight nautiloid cephalopods. This biofacies is interpreted to represent a nearshore or open bay eurytopic marine environment with periodically fluctuating conditions (particularly of salinity and bottom water dissolved oxygen) and may at times have had dysaerobic bottom water conditions. The thinly fissile, dark gray shale overlying the mudstone-limestone-mudstone lithofacies is much more sparsely fossiliferous, containing a few small brachiopods (mostly in limy and sideritic nodules), small straight nautiloid cephalopods, bivalves, and gastropods. This unit may represent marine bay conditions that periodically became more open marine. Nonfossiliferous gray shale and siltstone, grading upward into nonmarine fine sandstone and shale, overlie the Brush Creek marine zone here. This sequence is interpreted to represent prograding deltaic sedimentation across this area.