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.
AAPG Search and Discovery Article #91031©1988 AAPG Eastern Section, Charleston, West Virginia, 13-16 September 1988.