STRUCTURAL AND STRATIGRAPHIC/SEDIMENTOLOGICAL ANALYSIS OF PART OF THE MIDDLE ORDOVICIAN SEVIER FOREDEEP BASIN, SOUTHEASTERN GREENE COUNTY, TENNESSEE

Formation of the Sevier foredeep basin has long been debated, with models ranging from a foredeep to a complex basin prograding westward during the early Middle Ordovician Sevier-Blountian tectophase of the Taconic orogeny. Detailed geologic mapping of part of the easternmost exposed foredeep was recently completed. The stratigraphy consists of Knox Group carbonates unconformably overlain by Lenoir Limestone (and Mosheim Member), weakly cleaved lower Sevier Shale, and then by coarse limestone conglomerate at the base of a calcareous sandstone facies that forms the youngest unit exposed along the topographic crest. All units strike northeast and dip both northwest and southeast, preserving the Mid-Ordovician rocks in a synclinorium. Sandstone facies (and conglomerate matrix) microfabric includes strained and unstrained (annealed?) quartz, quartz with deformation lamellae, chert, microcline, felsic and mafic plagioclase [albite-oligoclase and arc-derived(?) labradorite], calcite, clays, and opaque minerals. Matrix and cement in all clastics contain a large proportion of carbonate. Conglomerate beds in the Sevier are similar in stratigraphic position and lithology to others in the southern Appalachian Valley and Ridge from Fincastle, VA, to Rockmart, GA. The conglomerate here is dominated by texturally varied, poorly sorted, well-rounded pebbles and cobbles of limestone and dolostone, possible clasts cannibalized from the Lenoir Limestone, and minor chert. The calcareous sandstone overlying lower Sevier Shale is thought to be too low in the stratigraphic section to be correlative with Keith’s “Tellico sandstone.” Our goals are to improve models related to the coarse clastic facies to unravel part of the history of the early Middle Ordovician Sevier foreland basin, and to understand the cause of platform uplift southeast of the Sevier basin that sourced the coarse clastic sediments.