No Abstract Avaliable

A subsurface investigation of the coastal areas in the Apalachicola delta region on the northwest Florida coast indicates that Pleistocene and Recent sediments thicken to the southwest and have been deposited on an uneven Miocene surface of variable age. All of the Pleistocene sediments are considered to be Sangamon or younger in age. The thickest Pleistocene section occurs west of the mouth of the Apalachicola River. It consists of two sequences of terrigenous clastic sediments, each grading upwards from coarse to fine, and represents two major Late Pleistocene sea level fluctuations. Radiocarbon dates and stratigraphic relationships indicate that the upper of these sequences probably represents a mid-Wisconsin transgression of the sea whereas the lower represents a Sangamon transgression. The thickest section of Recent sediments lies in the incised valley of the Apalachicola River which was cut during the last lowering of sea level. These sediments which consist entirely of deltaic, pro-deltaic, and bay sediments represent the gradual filling of the drowned river valley which was inundated by the Recent rise in sea level. The bays, barrier islands, and spits are the only other areas of any significant Recent sedimentation with the exception of one offshore basin to the southwest of the present river mouth and major barrier islands. Radiocarbon dates, stratigraphic relationships and environmental interpretations suggest that there was a relatively high stand of the sea which was very near present sea level sometime between 24,000 and 40,000 years B.P. Geomorphologic evidence in the area indicates that this high stand may have been slightly higher than present sea level and probably corresponds to the Silver Bluff shoreline of Florida and Georgia. No evidence has been found for a Recent higher sea level stand and radiocarbon dates and sediments indicate that sea level was approximately 10 to 15 feet below its present level sometime between 4,000 and 4,500 years ago.