FOSSIL COMMUNITIES OF THE PRODELTAIC NEW PROVIDENCE SHALE MEMBER OF THE BORDEN FORMATION (MISSISSIPPIAN), NORTH-CENTRAL KENTUCKY AND SOUTHERN INDIANA.

摘要

The New Providence Shale Member of the Borden Formation was deposited in the prodeltaic environment of the Borden delta. The Borden delta in north-central Kentucky and southern Indiana is the distal edge of a larger deltaic complex, termed the Borden-Cuyahoga-Grainer deltaic complex, which prograded from the Appalachian Basin to the eastern Interior Basin during Early Mississippian time. Within the New Providence there are two distinct fossil communities.; The older community, termed the Coral Ridge fauna, lived on the basin floor in front of the delta. This community contains 40 species, of which 29 are macrofossils. The goniatite cephalopods Beyrichoceras sp., Merocanites marshallensis, and Ammonellipsites sp. indicate an age equivalency of the Coral Ridge fauna to faunas of the upper part of the Burlington Limestone. The Coral Ridge fauna is dominated by deposit-feeding mollusks. Several factors indicate that this fauna probably lived in a reduced oxygen (dysaerobic) environment. The community structure is similar to other dysaerobic faunas of Devonian and Pennsylvanian ages.; The younger community, termed the Button Mold Knob fauna, lived at the base of the delta slope. This community contains 129 species, of which 96 are macrofossils. Two new species of crinoids, Cyathocrinites astralus n. sp. and Lecocrinus? springeri n. sp., are described from this community. The Button Mold Knob fauna is age equivalent to the faunas of the Keokuk Limestone. The Button Mold Knob fauna consists almost entirely of suspension feeders that lived under conditions of normal oxygenation. The fauna was studied by collecting 74 bulk samples that had a combined weight of 477 kg. The dominant groups of crinoids were nonpinnulate, which suggests lack of abundant phytoplankton, and filter feeding by motile-particle capture. A population study of the brachiopod Rhipidomella oweni (Hall and Clarke) indicates high juvenile mortality that probably was caused by smothering in mud. Biometric analysis of the abundant tabulate coral Cladochonus crassus (M'Coy) allowed reconstruction of the original size and form of the corallum.; The macroinvertebrate species diversity found in the rocks of the Borden delta is very similar to the macroinvertebrate species diversity of the Holocene Mississippi delta region. This strongly suggests that there has not been a significant change in within-habitat species diversity from the late Paleozoic to the Holocene.