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 lowgrade 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 northwest. Most longitudinal currents as far north as New Jersey flowed northeast whereas southwestward flowing currents predominated farther north. Graywackes in the north have much more quartz and slightly more feldspar and metamorphic rock fragments than those in the south. 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 northeast flowing longitudinal currents. The turbidity currents flowed down the sub-sea slope of a landmass ("Appalachia") locate to the southeast. Many currents which reached the bathymetric axis of the basin changed course and flowed longitudinally down the regional plunge.