Detailed subsurface well-log correlation and mapping revealed a regional unconformity (the sub-Ravencliff) and associated incised valleys at the base of the Ravencliff Formation of the Upper Mississippian Mauch Chunk Group in central and southern West Virginia. The sub-Ravencliff unconformity, a type-1 sequence boundary, forms the lower bounding surface of the Ravencliff-Pocahontas sequence that is bounded above by the sub-New River unconformity.
Although tectonic control is evident as is indicated by the southeasterly tilted sub-Ravencliff strata, the extensive regional truncation and channel incision at the sub-Ravencliff time may also have been influenced by a eustatic sea-level fall. In response to the fall of relative sea level, the shoreline retreated southward over 100 miles from the Avis to Ravencliff time. Consequently, incised valleys carved into the exposed shelf as deep as 160 feet with width ranging from 10 to 30 miles.
The incised valleys were filled during the subsequent rise in relative sea level with fluvial quartzose sands (the Ravencliff sandstone), derived primarily from the northern cratonic source. As relative sea-level rise continued, the incised valleys were turned into estuaries, filled with muddominated deposits of tidally-influenced environments. Maximum marine flooding represented by the highly radioactive Pride Shale of the Bluestone Formation was followed by the northwestward progradation of the Bluestone-Pocahontas clastic wedge. Regional uplift and coeval eustatic sealevel drop during latest Mississippian and Early Pennsylvanian emerged most of the central Appalachians and ended the Ravencliff-Pocahontas sequence.
AAPG Search and Discovery Article #90926©1999 AAPG Eastern Section Meeting, Indianapolis, Indiana