The Sedimentology of the Snowden Member of the Late Precambrian-Early Cambrian (?) Harper's Formation in Central Virginia

Abstract

The Snowden Member is the thickest and most mappable of the quartzose sandstone units of the heterogeneous Harpers Formation, the middle unit of the late Precambrian-early Cambrian(?) Chilhowee Group in central Virginia. Petrographic analysis statistically classifies the Snowden as a quartz arenite that has been locally altered through pressure solution to a quartzite. The overall textural and compositional homogeneity of the Snowden, one of its most striking features, presumably reflects both the provenance and depositional environment of the sediment. The Snowden was derived from the predominently chemical weathering in a humid environment of a low-lying, mixed source terrain of Precambrian high-grade metamorphic rocks (schists and gneisses), acidic plutons, and pre-existing sedimentary rocks located northwest and proximal to the depositional basin. Deposition occurred in an offshore linear barrier island or bar setting during a period of time where the rate of influx of sediment was low enough to allow the reworking of sediment already present or slowly entering the depositional basin . The models of the provenance and depositiona l environment of the Snowden support the more generalized sedimentary framework p roposed previously for the Chilhowee Group in central Virginia.