Paper No. 42-5
Presentation Time: 9:00 AM-6:30 PM
PRELIMINARY EVALUATION OF AN UNUSUAL LIMESTONE-PEBBLE CONGLOMERATE FROM THE UPPER HINTON (MISSISSIPPIAN) FORMATION OF SOUTHERN WEST VIRGINIA, U.S.A
The Hinton Formation of southern West Virginia is a complex, heterolithic, stratigraphic unit comprised primarily of terrestrial siliciclastic sedimentary rock, dominated by mudstones and laterally discontinuous sandstones. The upper Hinton includes two marine zones, the Eads Mill and Fivemile members that include a combination of organic-rich shale and carbonate. Limited exposures of a limestone-pebble lithology found within the upper Hinton displays an unusual combination of constituent grains including: rounded limestone, weathered plant material, detrital pyrite, mudstone clasts, marine invertebrate fossils, and silt-sized quartz. Outcrops of this material are cross-bedded and weathered into karst patterns. The rock is predominantly cemented with calcite with some pyrite. Grains commonly display a weathering rind of variable thickness. In some cases the rind is pyritic. The grains are mostly limestone (94%) with minor amounts of pyrite and quartz; most of the grains are rounded or subrounded (65%); and coarse sand or greater in size, occasionally up to 6 cm. The samples collected to date are grain-supported suggesting a sediment gravity flow. Three common interpretations are: tempestite, debris-flow, or fluvial flood. The Hinton is generally thought to represent coastal deposition in a subsiding foreland basin with high sediment influx. All of these interpretations are feasible, except for debris-flow, in this setting. Further work will establish a stratigraphic and depositional framework to differentiate between these interpretations.