Abstract

Samples of Recent and Pleistocene sediments collected along beaches, rivers, across a coastal island, and from the two lower Pleistocene terraces of the Georgia Coastal Plain have been analyzed by mechanical and petrographic methods. Comparison of results indicates that sedimentary parameters are similar for present and older shore lines, but that heavy-mineral suites differ in impoverishment of less stable mineral species in the older sediments. Comparison of measured and theoretical median diameters of the heavy-mineral suites also reflects the chemical decay process in the Pleistocene sands which is attributed to intrastratal solution action since deposition.

Sediment studies across southern Jekyll Island indicate a probable Recent age based on mineral and morphological data. Dynamic agencies operating along the coast are related to unusual concentrations of heavy minerals. Black sand concentrations in the upper littoral beach area, effected by water separation, reflect selective sorting of heavy-mineral species related to density and particle shape. Foredunes and parallel dunes in proximity to upper beach concentrates of heavy minerals contain several times the amount of heavy minerals as more normal beach and dune sand and reflect a ratio of heavy-mineral species intermediate between the water concentrates and average sand.

Application of heavy-mineral data derived from Recent coastal sediment could aid in interpretation of Pleistocene terraces and in exploration for ore minerals occurring in the sediment.

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