Pocono Dome, West Virginia--Catskill Island or Fantasy Island?

Kenneth J. Englund, Steven E. Brown, Thomas Dutro, Jr.

The Pocono dome (or Catskill Island) of east-central West Virginia traditionally has been recognized as a Late Devonian positive element overlain by a thin sequence of Lower Mississippian strata. The Pocono Formation and Maccrady Shale are inferred to be thin or absent at the crest of this dome or island because of nondeposition or erosion along an unconformity between the Upper Devonian Hampshire Formation and the Upper Mississippian Greenbrier Limestone. In contrast, our recent studies in southern and east-central West Virginia provide both lithostratigraphic and biostratigraphic data to challenge the existence of a Late Devonian dome or island. Lithostratigraphic data indicate an intertonguing relation between marine fossil-bearing conglomeratic sandstone beds of the P cono and terrestrial red beds of the Hampshire. As a result of intertonguing, lower beds of the Pocono wedge out approaching the "dome," and only the uppermost Pocono is present in the "crest" area. This relation is further corroborated by the presence of marine invertebrates, including Orthotetes cf. O. keokuk (Hall), Brachythyris cf. B. subcardiiformis (Hall), and Syringothyris subcuspidatus (Hall), which indicate that only late Osagian, or youngest Pocono, beds are present in the "crest" area. These data suggest that (1) the Pocono-Hampshire contact is diachronous and does not coincide everywhere with the Devonian-Mississippian boundary, (2) the Pocono "dome" represents the time-transgressive rise in the contact between intertonguing beds of the Pocono and Hampshire Formations, and (3 locally, the Hampshire Formation includes beds of Mississippian age in West Virginia.