Genetic stratigraphy and depositional systems of the upper Devonian-lower Mississippian Price-Rockwell deltaic complex in the central Appalachians, U.S.A.

Abstract

Rocks of the Price and Rockwell formations comprise the uppermost Devonian-Lower Mississippian deltaic complex in the central Appalachians. The Price Formation is dominantly marine and refers to all uppermost Devonian-Lower Mississippian rocks above either Hampshire Group red beds or the marine Greenland Gap Formation and below either the Greenbrier Limestone Group or Maccrady Formation red beds in the central Appalachians. The Rockwell Formation is dominantly non-marine and refers to equivalent rocks in south-central Pennsylvania and the Maryland-West Virginia panhandle region. Members of the Price Formation are generally equivalent to discrete genetic events. Price deposition was initiated in latest Devonian time when a regional transgression covered delta and alluvial plain facies of the Catskill deltaic complex with protected-bay and strandline facies of the Oswayo Member in West Virginia, Pennsylvania and western Maryland. Farther south, these transgressive facies overlie the Cloyd Conglomerate Member, a thin regressive-transgressive sedimentary wedge, and occur in the lower part of the Sunbury Shale Member. Subsurface Berea Sandstone deposition corresponded to regional exposure and erosion in the outcrop belt. This unconformable surface was overstepped in earliest Mississippian time by a major transgression that deposited a variably thick but persistent basal transgressive sandstone during shoreface retreat. Sandstones that have been referred to the “Cussewago Sandstone” in northern West Virginia and southwest Pennsylvania are part of this basal sandstone. Eastward, these sandstones thicken, coarsen and interbed with a polymictic diamictite at the base of the Rockwell Formation. Shaly facies of the earliest Mississippian transgression overlie the basal sandstone. The Riddlesburg Shale preserves offshore and open-bay facies in West Virginia that grade eastward to estuarine and restricted, back-bar lagoon and marsh facies of a barred-bay complex in south-central Pennsylvania and the Maryland-West Virginia panhandle. From central West Virginia, Riddlesburg facies grade southward into basinal facies of the Sunbury Shale Member. Syndepositionally active basement features, the West Virginia Dome and “Tri-State Block”, were structurally positive areas in the foreland basin. The “Tri-State Block” caused truncation of Lower Mississippian marine facies in western Maryland and large-scale westward erosional overlap of channel-fill sandstones in the upper Rockwell Formation. The West Virginia Dome was also structurally positive and the basal transgressive sandstone contains phosphatic omission surfaces on the dome crest. Lack of subsidence caused scour and incision of Riddlesburg facies by overlying deltaic facies. Progradation ensued with fluvial-dominant, shallow-water deltaic systems (Price Rockwell Member) in northern West Virginia and marine-dominant deep-water deltaic facies farther south. A 150 m minimum paleodepth estimate in the foreland basin is based on stratigraphic thickness in southern West Virginia. Following a transgression near the Kinderhookian-Osagean boundary. Price marine-deltaic facies form a coarsening-upward sequence to delta plain coals and coastal-alluvial plain red beds. A 35 m estimate for average storm wave base utilized tempestite proximal-distal trends.