RESOLVING UPPER PALEOZOIC STRATIGRAPHY IN EASTERN WEST VIRGINIA THROUGH GEOLOGIC MAPPING AND DETRITAL GEOCHRONOLOGY

Currently the geology of Randolph Co.,the largest county in West Virginia, is primarily documented in a 1:62,500-scale map. Our 1:24,000 EDMAP geologic mapping project in the Valley Head quadrangle fills a gap in Randolph Co. between areas to the north and south that have been mapped by the WVGES. Our project combines field data with detrital zircon and apatite U-Pb geochronology to characterize and identify Lower Mississippian-Upper Devonian stratigraphic units, which historically have been challenging to subdivide. Regionally, the Upper Devonian (Famennian) Hampshire Group has been subdivided into the lower marine-influenced Cannon Hill Fm. and upper terrestrial Rowlesburg Fm.; however, in the Valley Head region, the Cannon Hill Fm. is not observed. Thus, Hampshire-equivalent strata in the Valley Head area are classified as a formation. Above the Hampshire Fm. lies the uppermost Devonian-Lower Mississippian (latest Famennian-Tournaisian?) marine units of the Price Fm. (formerly known as the Pocono Group). In Valley Head, the Price Fm. is characterized as a ridge-forming, quartz-rich, pebble-to-granule conglomerate; however, shallow geotechnical borehole cores from near the Hampshire-Price contact in the Valley Head quadrangle show diamictite facies interpreted as glaciomarine deposits, which have not been observed in outcrop. We infer that these deposits belong to the latest Devoninan (Famennian) Oswayo Fm. (or Oswayo Mbr. of the Price Fm.), which represents the first documented occurrence of this unit south of the West Virginia Dome. Preliminary detrital zircon U-Pb data indicate the Price Fm. maximum depositional age (MDA) is 365.56 ± 4.01 Ma (Famennian). The upper Hampshire Fm. has a MDA of 370.66 ± 4.25 Ma (earliest Fammenian age). In contrast, two samples from the lower Hampshire Fm. yielded MDAs of 382.99 ± 4.87 Ma and 446.81 ± 3.68 Ma; these MDAs indicate either pre-Late Devonian deposition or predominantly recycled sediment influx, with the latter being our preferred interpretation. Preliminary detrital apatite U-Pb data from the lower Hampshire Fm. indicates a MDA of 422.11 ± 6.62 Ma, suggesting thermal reset and exhumation of apatite grains during Acadian orogenesis. Future work will compare these results with data from type Devonian-Missisipian strata exposed elsewhere in West Virginia.