CONODONTS AND AGE OF DEPOSITIONAL SEQUENCES IN THE CHATTANOOGA SHALE, UPPER DEVONIAN, SOUTHERN APPALACHIAN BASIN

The Chattanooga Shale unconformably overlies Ordovician to Givetian strata deposited in relatively quiet offshore water of the Appalachian Basin. Condensed sections in the distal basin show regional variation and contain numerous disconformities where the depositional pulses correspond to rises in sea level and black shale deposition in the northern part of the basin. In the Center Hill reference area of central Tennessee the basal 60 cm of the Dowelltown Member contains Palmatolepis bohemica over a disconformable surface and sandy lag bed that contains Ancyrodella rugosa, Mesotaxis asymmetrica, Polygnathus dubius and Po. linguiformis, indicative of MN zones 6-lowermost 8 over indicators of Givetian and lower Frasnian strata that were removed by erosion. The middle Dowelltown contains Pa. ljachenkoae and Ancyrognathus iowaensis, indicative of MN zones 9-11. The upper two meters of the Dowelltown contain Pa. bogartensis and Pa. juntianensis, indicative of MN Zone 13, as well as new taxa. Eastward the base of the Dowelltown Member disconformably overlies Givetian strata containing Klapperina disparalvea that are equivalent to the Geneseo Shale. Conodonts from the shale between several beds of the Belpre Ash include Pa. punctata, Pa. sp. H, and Ancyrognathus barba, indicative of MN Zone 8. The Gassaway Member consists of three informal subdivisions; the lower Gassaway is predominately black shale containing two distinct faunas that correspond to the depositional sequences recognized by Schieber based on lithology. The lower Gassaway contains a diverse L.-U. triangularis zones fauna and correlates with the base of the Dunkirk/Huron shales in the northern portion of the basin that is then overlain by a diverse U. crepida Zone fauna that correlates with a second depositional pulse and deepening of the Huron Shale. The middle Gassaway is lighter gray and contains a L.-U. rhomboidea zones fauna. The upper Chattanooga, consisting of predominantly black pyritic shales, contains Pa. marginifera and Pa. quadrantinodosa indicative of L.-Um. marginifera zones, which corresponds to a third deepening pulse in the Famennian.