| Summary |
Sedimentary strata between the Pocahontas No. 6 coal bed and the lowermost shales of the New River Formation were interpreted using outcrop and subsurface data in Bramwell and Grumpier 7.5' quadrangles. A facies model for the upper Pocahontas Formation was constructed. The study interval comprises a conformable sequence of interbedded sandstone, siltstone, shale, coal, and underclay deposited on an upper delta plain which prograded to the west into the Appalachian foreland basin. The Flattop Mountain Sandstone Member, uppermost unit of the Pocahontas Formation, is a fine- to medium-grained lithic arenite occurring as an ancient fluvial meander belt that pinches out to the north. The unit is similar in appearance and composition to other upper Pocahontas channel sandstones. An abundance of polycrystalline quartz and metamorphic rock fragments indicates a recycled orogen source area to the east. Rocks of the study interval have been divided into two general facies assemblages: a channel belt sandstone and an overbank-floodplain. Assemblages have been subdivided into six objectively defined lithofacies: A) fluvial channel sandstones; B) crevasse splay sandstones and siltstones; C) backswamp-floodplain shales and siltstones; D) leveeoverbank and distal crevasse splay lobe deposits consisting of interlaminated sandstone, siltstone, and shale; E) rooted underclays; and F) coal and carbonaceous black shales deposited in peat swamps. Lithofacies commonly display preferred fining-upward lithic transition cycles characteristic of fluvial deposits. |
