CONODONTS AND SEQUENCE STRATIGRAPHY IN THE UPPER DEVONIAN MARINE CLASTIC-DOMINATED STRATA OF THE NORTHERN APPALACHIAN BASIN

Third Order sequences in Upper Devonian strata of the Appalachian Basin are demarcated by the development of widespread black shales that form the bases of the lithostratigraphic subdivisions. The black shales have long been interpreted as transgressive in nature. Near or at the base of each extensive black shale is a bed that contains a high concentration of conodonts, as well as fish material, plant remains, and often detrital pyrite. These are the Leicester Pyrite at the base of the Geneseo (high Givetian), North Evans - Genundewa Limestone at the base of the West River, Williamsburg Bed near the base of the Middlesex, and Weyer Bed at the base of the Rhinestreet Shale; the Pipe Creek (upper Frasnian) and Dunkirk shales (lower Famennian) break this trend. These conodont-rich beds are interpreted as the maximum starvation interval of the sequence coinciding with or followed by maximum flooding, and then the accumulation of black and dark-gray shale during the highstand interval. Coarse clastic, carbonate and conodont-rich beds within the major sequences can be related to shallowing and deepening within smaller scale cycles. Conodonts recovered from the more offshore portions of the clastic-rich strata of the Appalachian Basin enable biostratigraphic correlation of major sequences outside the basin and point to sub-zonal refinements utilizing smaller-scale cyclic sequences.