ABSTRACT

Mineralogical analyses of suspended sediments and bottom sediments from three Georgia estuaries (Altamaha, Ogeechee, and Satilla Rivers) indicate that the clastics of this area are a mixture of fluvially derived Piedmont and Coastal Plain detritus, and fines derived from the continental shelf. High illite-montmorillonite clay suites are transported into the estuaries from offshore during flood tide, whereas kaolinite plus minor mixed-layer clay, vermiculite and talc from the Piedmont and montmorillonite from the Coastal Plain and/or paralic sediments characterize the upstream and intermediate areas of mixing within the estuaries. Decreasing flow velocity and flocculation of the clays, probably induced by salinity changes, results in a general change in bottom sediments from sand in th rivers to clay in the estuaries.

Sands and silt fractions are high in quartz with significant amounts of feldspar in the Altamaha (Piedmont source). Heavy-mineral composition of these sediments reflects the proportionality of the division of the drainage basins between the Piedmont and the Coastal Plain. The former is characterized by unstable suites, whereas the latter contributes stable to ultrastable assemblages. Sorting is generally poor reflecting a variety of processes which influence the sediments within the estuary.

The work amplifies the conclusions of previous workers that shoreward transport, especially for the fine fraction, is an important process in determining the composition of the estuarine sediments.