PALEOECOLOGY OF BRYOZOANS FROM A CHESTERIAN DARK SHALE INTERVAL WITHIN THE BANGOR LIMESTONE, SCOTTSBORO ALABAMA

A unique 13-feet thick interval of dark shale in the Bangor Limestone unit located in the Vulcan Materials Quarry, two miles west of Scottsboro Alabama, contains abundant fossils. Bryozoans and ostracodes dominate the interval; secondary taxa include brachiopods, bivalves, gastropods, rugose corals, trilobites, and cephalopods. Previous paleoecological interpretations of bryozoan-ostracode faunas provide a framework for interpretations of our studied interval. The growth forms of bryozoans, and the ornamentation, abundance, and diversity of ostracodes were used to interpret the paleoecological setting of the shale including sedimentation rate, substrate character, salinity, water energy, and water depth.

Erect rigid delicate branching and erect rigid fenestrate bryozoan colonial growth forms dominate the shale interval. The dominance of these bryozoan colonial growth forms indicates a paleoenvironment of 50 to 200m water depths, low strength subtidal to geostrophic currents, low sedimentation rate, and a stable substrate that is moderately firm. Ostracodes in the shale interval are correlatives with the Amphissites biofacies of Carboniferous and early Permian cyclothemic sedimentary sequences of the Mid-continent of North America. The presence of this biofacies indicates an offshore paleoenvironment of moderate water depth. The combined evidence of bryozoan and ostracode depth associations suggests that the environment of deposition of the shale interval was an outer marine shelf with water depths of about 200 meters. Currents were of low strength, the sedimentation rate was low, and the substrate was stable and moderately firm.