Quaternary Surface Formations of Southern Part of Atlantic Coastal Plain

Abstract

The Citronelle formation of the eastern Gulf Coast region extends northward across the coastal plains of Georgia, South Carolina, North Carolina, and Virginia as a gravelly sand formation 100 feet thick, covering 30,000 square miles of upland area. These deposits were shown on early geological maps as the "Lafayette" or "Altamaha" formation, of Late Pliocene or Early Pleistocene age. In more recent geological reports the deposits have been ignored or included in the underlying Tertiary and Cretaceous formations; miscorrelations at state boundaries are involved in these later interpretations. Determinations of "older than (Nebraskan) Pleistocene" made on plant fossils found in the surface Citronelle in Alabama and the presence of Calabrian index fossils, the cold-water Foraminifera, Hyalinea balthica, and Globigerina inflata, in the subsurface Citronelle in southern Louisiana, indicate an Early Pleistocene (preglacial) age for the formation. Deposition of the formation in the Atlantic Coast region occurred on a peneplain developed during a technically quiet time in the Late Miocene and Pliocene and was caused by the first of a series of uplifting and warping movements which affected the coastal and adjacent mountain regions. These movements, which separate the present cycle of erosion and deposition from the preceding period of peneplanation, provide a sounder geological basis for the division of the Tertiary and Quaternary periods than does the post-Citronelle initiation of Pleistocene glacial climate.