An Appraisal of the Evolution of the Lower Atlantic Coastal Plain of Georgia, U. S. A.

Abstract

IN EDINBURGH in 1785 James Hutton proposed the doctrine of uniformitarianism, 'the present is the key to the past', implying that, given sufficient time, processes now at work can account for all geological features. It is considered that Hutton's statement is particularly pertinent to the study of barrier1 coasts because of some difficulties in understanding littoral constructional features. Erosion, progradation and the reworking of sediments are important shore and nearshore processes that modify coastal accumulations prior to their incorporation in the geological sequence. It is necessary to understand the changes produced near the modem shoreline2 in order to interpret the origin of the preserved sediments. In this connection, coastal Georgia is a particularly significant area, because ancient sediments are generally well preserved and provide a comprehensive record of the geomorphological and sedimentary history of the region. Therefore it is possible readily to compare the modern and the ancient, and to study the ancient in several stages of modification. Also, because the major features are depositional, it is possible to establish a sequence of changes of sea-level. An attempt is made in this paper to outline the Quaternary history of the lower Atlantic Coastal Plain of Georgia, and to discuss some of the chronological problems facing the geomorphologist in attempting to establish late Pleistocene eustatic changes of sea-level. The area is described in detail because it is considered to have been relatively stable during the Quaternary and may be considered as a key to the problem of eustatic changes of sea-level. There is no evidence to suggest warping or tilting, and since Georgia has not been glaciated, there is little difficulty in separating the effects of glacio-isostasy from eustatic changes of sea-level. Road and rail cuttings, natural exposures and pits provided evidence for evaluating stratigraphical relations in the field. In addition, several hundred shallow boreholes were sunk using a truck-mounted core drill, and by hand augering. The results of field investigations were supplemented by information obtained from aerial photographs and from standard topographical maps (7½- and I5-minute quadrangle sheets) of the United States Geological Survey. The size distribution of samples collected from the boreholes was obtained by conventional sieving methods. Graphical and moment measures were computed for all samples, details of which appear in a separate publication (Hails and Hoyt, in the press).