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Sycamore Grit Siltstone: Informal Member of Upper Devonian in North-Central West Virginia

Larry J. Cavallo

The Upper Devonian Sycamore grit siltstone (an informal member of the Brallier Formation) was studied both in outcrop and subsurface. Outcrops consist of approximately 80 ft of thin to medium-bedded, brownish-gray, argillaceous siltstones and olive-gray shales. The Sycamore was presumably deposited by or associated with turbidity currents, because sedimentary structures include incomplete Bouma sequences and flute casts. Petrographic studies from outcrop sections reveal quartz, plagioclase, feldspar, and micas as the dominant framework grains; the matrix is composed of ductile grains and finer detrital material. Porosity is very low in these outcrop samples due to pore filling and grain coating by chlorite and hematite.

The subsurface portion of the study was conducted over a 12-county area of north-central West Virginia, where the Sycamore occupies a stratigraphic position approximately 1,500 ft below the Benson sand and 800 ft above the Tully Limestone. Areally, the Sycamore appears as a series of submarine fans and attains its maximum thickness where two or more of these fans overlap. Near Weston, in central Lewis County, the Sycamore grit siltstone reaches a thickness of 90 ft and is a proven economic producer of natural gas when dually completed with shallower formations.

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