STRUCTURAL AND STRATIGRAPHIC ANALYSIS OF PART OF A MIDDLE ORDOVICIAN SYNCLINE NEAR MT. VERNON, TENNESSEE

A regional Alleghanian syncline in the eastern southern Appalachian Valley and Ridge extends from SE Tennessee into SW Virginia in the footwall of the Great Smoky thrust, and preserves Cambrian to Mississippian rocks. The erosional resistance of two Middle Ordovician (MO) clastic units produces topographic expression that outlines the SW end of the structure between Etowah and Sevierville, TN. The hinge has a NE trend and a gentle NE plunge; a plot of poles to bedding produces a great circle girdle with an axis at 065, 04°. Weak axial-planar cleavage is developed in the Bays Formation in the core of the syncline. The MO sequence is the product of deposition in the Sevier foredeep basin and basin margin. Deposition followed rapid subisdence resulting from isostatic compensation of Taconian thrust loading of the eastern Laurentian margin. The Lenoir Limestone-Athens Shale transistion reflects initiation of basin subsidence, as the shallow-water carbonate bank was drowned by subsidence and deposition of deep-water marine clastic sediment into the sediment-starved basin. The hematitic Chapman Ridge Sandstone, overlying the Athens, may have had a source in the western Blue Ridge by cannibalization of older rifted margin clastics, with the hematite derived from oxidation of massive sulfides. The Sevier Shale above the Chapman Ridge filled the basin with turbidite deposits in a submarine fan complex. As the basin filled and water shallowed, bryozoan reefs formed local carbonate banks that were then drowned by more subsidence and renewed rapid Sevier clastic deposition. The higher energy silt and fine sand of the oxidized Bays Formation above the Sevier represents the end of the foredeep cycle.