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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 63 (1979)

Issue: 5. (May)

First Page: 846

Last Page: 847

Title: Silurian-Devonian Embayment into Appalachia: ABSTRACT

Author(s): Richard A. Smosna, Douglas G. Patchen

Article Type: Meeting abstract


Several Silurian and Devonian formations, traced along central Appalachian outcrop belts, undergo anomalous changes in lithology, thickness, and faunal content in the area of Previous HitPendletonNext Hit County, West Previous HitVirginiaNext Hit. Hematitic sandstones are replaced by nonred sandstones, other sandstones change to shales, shale formations thin and pinch out, and Catskill red beds are replaced by nonred clastics. These changes represent a move from nearshore to more offshore deposition within an embayment along the western shoreline of Appalachia.

The principal Silurian sandstones, the Tuscarora, Keefer, and Williamsport, all undergo facies changes in this area, becoming finer grained, argillaceous, and/or calcareous. Hematitic nearshore sandstones of the Rose Hill are replaced by nonred sandstones in the embayment. The Rochester and Rose Hill shales are thickest in, and largely confined to, the embayment; younger shales, the Big Mountain and Mandata, are replaced by sandstones south of the embayment. McKenzie shales contain more interbedded limestones in the embayment, and the fossiliferous middle Tonoloway Limestone contains a different fauna there than in adjacent areas. During Middle Devonian time, thicker, deeper water Needmore Shale beds in the area were flanked by shallower water facies of the Onesquethaw. The Mahantango Formation also is thickest in this area and thins abruptly to the south.

Throughout this time two provenances supplied detritus, one east of West Previous HitVirginia'sNext Hit eastern panhandle and the second in central Previous HitVirginiaNext Hit. The Previous HitPendletonTop embayment was situated between these two regions that occasionally prograded westward, accentuating the embayment. For the final Devonian regression these areas are

End_Page 846------------------------------

referred to as the Fulton and Augusta lobes of the Catskill delta, separated by Grant bay.

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