Stratigraphy along Chattahoochee River, a Connecting Link between Atlantic and Gulf Coastal Plains: ABSTRACT

Abstract

The geologic section along Chattahoochee River is one of best and most complete in Coastal Plain of United States. It is only continuous unweathered section of Cretaceous and Tertiary beds in southeastern Alabama and southwestern Georgia, and comprises a connecting link between well-known standard section and type exposures to west in Alabama and beds to east in Georgia and South Carolina. It is also an important section because of its intermediate position between clastic facies in central and western Gulf Coastal Plain and equivalent carbonate facies in subsurface in Florida. Upper Cretaceous, Paleocene, lower Eocene, and middle Eocene strata are exposed in an almost continuous section down dip from crystalline rocks at Fall Line at Columbus, Ga., to upper Eocene exposures about 8 miles north of Alabama-Florida boundary, a distance of 126 miles. This study of a part of that section supplies detailed stratigraphic and structural information on rocks of Tertiary age that are exposed southward from Upper Cretaceous-Paleocene contact 15 miles south of Eufaula, Ala., to exposures of upper Eocene Crystal River limestone of Moore, 1955, 15 miles south of Columbia, Ala., a distance of 49 miles. The total thickness of Paleocene, lower Eocene, and middle Eocene strata in this part of river is a little over 600 feet. The average dip is 15 feet per mile to south, but in places beds are horizontal for distances of as much as 3 miles. The formations recognized in river section are those in standard Alabama stratigraphic section. From bottom up they are Clayton formation of Paleocene age, Nanafalia formation, Tuscahoma End_Page 1258------------------------------ sand, and Hatchetigbee formation of lower Eocene age, and Tallahatta and Lisbon formations of middle Eocene age. Stratigraphic sections for these studies were combined into longitudinal profiles for left and right banks of river, an arrangement that visually describes detailed lithology and structure. Horizontal control was from aerial photographs. Vertical control was from river surface. The altitude of river surface was determined from stage of river referenced to the thalweg, as plotted by U. S. Corps of Engineers, and bench marks of U. S. Coast and Geodetic Survey. The use of the thalweg in determining altitudes of contacts permits rapid and accurate mapping of geologic sections along rivers. End_of_Article - Last_Page 1259------------