Abstract

The Mechum River Formation is a thick succession of metamorphosed conglomerate, sandstone, siltstone, and shale exposed within a narrow, elongate structural infold (the Batesville syncline) along the axis of the Blue Ridge anticlinorium in central Virginia. The thickness of the unit is variable, ranging from approximately 1500 to 3000 ft. Stratigraphic position suggests that the Mechum River Formation may be at least partly correlative with the Swift Run and Lynchburg Formations, but there is no specific faunal evidence for age or correlation. Sedimentary petrology indicates that the unit was derived from uplifted parts of the igneous and metamorphic rocks of the Virginia Blue Ridge Complex which the Mechum River Formation overlies with profound unconformity. A variety of depositional environments (alluvial-fan?, channel fill, point bar, braided stream, and floodplain facies) can be inferred for the unit on the basis of texture and vertical succession of sedimentary structures, but it is not possible to specifically interpret the relative importance of each of these nonmarine environments. Crossbedding azimuths from the southeastern margin of the unit point southwest, those from the northwestern margin point south and southeast. This crudely centripetal paleocurrent system may reflect the existence of an elongate basin extending northeast-southwest. Such a basin may relate to the separation of North America from Africa and the opening of the Paleozoic Protoatlantic Ocean. However postulating such a basin solely on the basis of the evidence in this paper would be speculative.

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