Erwin Formation (Lower Cambrian) of Northeast Tennessee: Evidence for Storm-Dominated Shelf: ABSTRACT

Abstract

The Erwin Formation of northeast Tennessee consists of three facies, which are thought to indicate deposition on a storm-dominated shelf. Facies A consists of interbedded siltstone and hummocky-stratified, fine-grained sandstone. Commonly, in facies A, 1 to 8-m sequences coarsen and thicken upward. These sequences are interpreted to represent storm wave deposition below fair-weather wave base. The thicknesses of sandstone beds reflect the proximity and intensity of storms or the quantity of sediment available, or a combination of both. Facies B is characterized by medium to large-scale, planar-tabular and trough cross-stratified sandstone and rare siltstone interbeds. This facies commonly succeeds facies A upward in a vertical sequence. Facies B is thought to have been deposited by storm-generated, unidirectional currents on the shoreface. Facies C consists of very thick-bedded, medium to very coarse-grained, supermature sandstone. The sandstone appears to be crudely cross-stratified, and interbedded siltstone or shale is completely absent. Facies C is interpreted to have been deposited on the upper shoreface during storm erosion of the foreshore and nearshore zones. High textural and compositional maturity indicates constant agitation and winnowing of the sediment on the shoreface. The three facies of the Erwin Formation are arranged in two 50-m thick, coarsening-upward sequences,more » in the order A, B, C. These sequences are thought to represent two depositional pulses in which shoreface sand prograded over shelf sediment.« less