Trace Fossils from Storm-Influenced, Oxygen-Deficient Outer Shelf: Lower Mississippian Price Formation of Southern West Virginia
Thomas W. Bjerstedt
The Price Formation in southern West Virginia was deposited dominantly in an oxygen-deficient, outer shelf environment along a siliciclastic profile from the basin plain to the alluvial plain. An overturned section at Bluefield, West Virginia, exposes the following lithofacies and environments in ascending order: laminated black silt-shales from the basin plain; a sand-rich submarine fan; outer shelf tempestites of hummocky, cross-stratified fine sandstone and completely bioturbated grayish-black, silt-shales; and shoreline sands in transition to thin, dirty coals of the coastal plain and Maccrady red beds of the alluvial plain.
Trace fossils are abundant and are best preserved on the soles of hummocky, cross-stratified sandstones. The Zoophycos ichnofacies occurs throughout 80 m of outer shelf deposits, which accumulated above storm wave base. The Zoophycos ichnofacies grades into the nearshore Skolithos ichnofacies with no apparent intervening Cruziana ichnofacies. Most ichnotaxa identified from the outer shelf are fodinichnia or pascichnia. Planar and helical Zoophycos, Helminthopsis, Helminthoida, Sclarituba (Neonereites form), and Chondrites are characteristic.
In most schemes, the Zoophycos ichnofacies occurs below storm wave base. At Bluefield, it has displaced the Cruziana ichnofacies above storm wave base due to the maintenance of a dysaerobic environment.
The abundant organic matter preserved in a density-stratified water column was continually replenished during periods of upwelling. Conditions were extremely favorable for deposit feeders, but inhibiting to suspension feeders that were less tolerant of oxygen stress. The absence of distributary channel sands in the vertical sequence also indicates that offshore environments received no influx of oxygenated waters from the Price delta.
AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.