Abstract

Sedimentary attributes of the Martinsburg (Ordovician) Formation were studied between Staunton, Virginia, and Kingston, New York. Graded bedding, sole marks, intraformational shale fragments, convolute and small-scale cross-lamination of the flysch-type Martinsburg graywackes suggest a turbidity current origin. These turbidites are interbedded with gray pelagic shales, in places graptolite-bearing, and locally with radiolarian cherts. The composition of the graywacke indicates that the chief source was sedimentary and low-grade metamorphic rocks; acid plutonic rocks were a secondary source. Many rock fragments were derived from the Martinsburg itself. Sole marks, chiefly groove and flute casts, show paleocurrent trends to be parallel (longitudinal), oblique, and perpendicular (transverse) to the present strike. The transverse currents flowed generally toward the NW. Most longitudinal currents as far N. as New Jersey flowed NE. whereas southwestward flowing currents predominated farther N. Graywackes in the N. have much more quartz and slightly more feldspar and metamorphic rock fragments than those in the S. This difference is not accompanied by a northward decrease in grain size and cannot be due solely to sorting during transport; hence lateral supply is required even for the NE.-flowing longitudinal currents. The turbidity currents flowed down the sub-sea slope of a landmass ("Appalachia") located to the SE. Many currents which reached the bathymetric axis of the basin changed course and flowed longitudinally down the regional plunge.

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