--> Abstract: Distinctive Turbidite Siltstone in Devonian Brallier Formation of West Virginia and Virginia, by Katharine Lee Avary, John M. Dennison; #90961 (1978).
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Abstract: Distinctive Turbidite Siltstone in Devonian Brallier Formation of West Virginia and Virginia

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A distinctive package of siltstones in the lower part of the Brallier Formation has been identified throughout an area 75 mi (120 km) long by 30 mi (48 km) wide in 43 outcrops in the foldbelts of West Virginia and Virginia and in wells in Pocahontas and Randolph Counties, West Virginia. Informally called the Back Creek siltstone, this package is distinguished from the rest of the Brallier by greater concentration and thickness of individual beds and the stratigraphic position of its base about 150 ft (45 m) above the Tully Limestone. Individual beds are up to 5.6 ft (1.7 km) thick. Bed thickness and total thickness decrease northward, westward, and southward.

Individual siltstones generally have an abrupt base and are interbedded with moderately dark gray, thickly laminated shale. These represent the D and E zones of the Bouma sequence. The abrupt north and south terminations seem to be lateral margins of turbidity flows. Limited flute- and groove-cast data indicate a westward-moving current.

These siltstones are the earliest manifestation (middle Finger Lakes) of the Catskill delta Augusta Lobe, a lobe which persisted at least until deposition of the Cassadaga. Development of this new lobe probably oversteepened the basin margin. Absence of simultaneous siltstone packages on other delta lobes argues against sea-level fluctuation as a cause for this clastic wedge.

Younger Devonian turbidites farther west in the Appalachian basin are the focus of active hydrocarbon interest. Outcrops of Back Creek siltstone provide an exceptional opportunity to study similar exploration targets.

AAPG Search and Discovery Article #90961©1978 AAPG Annual Convention and Exhibition, Oklahoma City, Oklahoma