Citronelle Age Problem

Abstract

The Citronelle formation of the Gulf Coast region has been considered, on the evidence of fossil plants, to be late Pliocene in age, but some geologists have thought that it may be basal Pleistocene because of its unconformable relations with the underlying Tertiary formations and its close associations with the overlying Pleistocene formations. In this paper it is shown that the fossil evidence supports no more than a pre-Nebraskan determination, thus making an early Pleistocene correlation as plausible as one of late Pliocene. As a result of the 1948 definition of the Pliocene-Pleistocene boundary by the 18th International Geological Congress, the Pleistocene, in its European type locality, now appears to include a pre-glacial (pre-Gunz, pre-Nebraskan) section, the Calabrian-Villafranchian, and possibly part of the Sicilian. Evidence is presented which suggests that equivalent sections in the United States are: Mid-Continent region, Blanco; Atlantic Coast, Citronelle and Sunderland; Gulf Coast, Citronelle and Duck Lake; Pacific Coast, Pedroian and Sierran. In the Gulf Coast region the Citronelle is shown to be the surface equivalent of the basal member of a 3,000-4,000-foot subsurface Pleistocene section. An overlying member of the subsurface section is here named the Duck Lake formation. Succeeding members are correlated with the surface Lissie, Oberlin, and Eunice formations of south Louisiana. These, in turn, are correlated with the glacial Pleistocene deposits, Aftonian, Yarmouth, and Sangamon.