ABSTRACT

Cretaceous and Tertiary sediments, with maximum thickness of about 8,000 feet in southwestern Georgia and 18,000 feet in the South Florida Basin, are present under all of the area south of the Appalachian Piedmont belt of Precambrian (?) crystalline rocks. In addition, flat-lying early Paleozoic sandstone and shale underlie northern Peninsular Florida and southernmost Georgia; Triassic continental deposits, with diabase sills and dikes, are in grabens under parts of the Georgia coastal plain and northern Florida; and Jurassic terrigenous clastics, carbonates, and evaporites probably occur on the western and southern flanks of the Peninsular Arch.

Limestone and dolomite comprise most of the Cretaceous and Tertiary section. Anhydrite is abundant in the Lower Cretaceous and Paleocene deposits, and sandstone and shale occur throughout the section in Georgia near the northern edge of the coastal plain. Deposition was in shallow marine environments on an extensive slowly subsiding shelf. The southern Appalachians were of low relief and, after Lower Cretaceous time, little sediment from this bordering land was transported to the shoreline of the shallow sea. There were, however, several minor marine transgressions and regressions in southern Georgia during the Upper Cretaceous and Tertiary periods, due to changes in the rate of uplift of the bordering land and downwarp of the coastal plain and adjacent marine areas. The regressive deposits, with sands were deposited slowly, and they were reworked during the succeeding advances of the sea.