PALEOECOLOGY OF CARBONIFEROUS (CHESTERIAN) OSTRACODA FROM A BLACK SHALE WITHIN THE BANGOR LIMESTONE AT SCOTTSBORO, ALABAMA

Ostracodes from seven continuous channel samples from a 13-foot sequence of black shale within the Bangor Limestone (Carboniferous, Chesterian; Scottsboro, Alabama) were analyzed in order to determine their environment of deposition. There is little obvious change in lithic type within the studied interval.

Almost all of the ostracode species exhibit a wide range of instar sizes indicating there was little transportation of the fauna. From 2 feet to 8 feet above the base of the unit the shale contains an ostracode fauna that is moderately abundant (more than 500 adult or large instars per kilogram), very diverse (28-29 species), and has a equitable distribution of species. Many of the species in this lower part of the belong to genera with reticulate or pitted carapaces (Polytylites, Shleesha, Moorites, Kirkbya, Ectodemites, Coronakirkbya); many others exhibit spines (Healdia, Pseudoparaparchites). The upper part of the shale (especially the uppermost 2 feet) has a somewhat less diverse (21-25 species) ostracode fauna. Ostracode faunas in the upper part are characterized by high abundance and high dominence. Specimens of a single (?) species of the genus Cavellina in this upper part compose 70 percent of the fauna. The upper part is largely characterized by ostracodes with smooth carapaces (Cavellina) or spines.

Comparisons of abundance, diversity, morphology and taxonomic content of these Chesterian faunas with Pennsylvanian ostracode faunas occurring in midcontinental cyclothems suggest a marine, mid- to outer shelf environment for the lower part of the sequence. The upper part of the sequence may represent more onshore, shallower water environments than the lower part.