Middle Eocene Calcareous Nannofossils at Little Stave Creek, Alabama

Abstract

The middle Eocene Claiborne Group at Little Stave Creek, Alabama, contains a rich and varied assemblage of coccolithophores, with a significant development of provincial forms such as pentaliths, rhabdoliths, and holococcoliths. The pentaliths of the family Braarudosphaeraceae are especially well-developed in the study area. These provincial forms are known from hemipelagic marine deposits in numerous areas, but are notably lacking or sparse in oceanic pelagic sediments. The pentaliths are rare in contemporary nannofloras, but several other Recent coccolithophores have a provincial distribution that is attributed to a benthonic phase in the life cycle of the organism. Eocene pentaliths and the other provincial species may have had similar limitations; nevertheless, they must have possessed a phase which was capable of traversing the open ocean because the same species occur in hemipelagic sediments on all continents. The apparent provincialism of these forms does not diminish their usefulness because the occurrence of a particular species is synchronous throughout the geographic range of that form. These species are useful, therefore, both as stratigraphic indicators in Paleogene sediments and as environmental indicators of the hemipelagic realm.