Abstract

The lower Georgia Coastal Plain consists of six Pleistocene barrier island coastlines. Each barrier sequence can be sub-divided into lagoon-salt marsh and barrier island facies. The former include estuary and tidal channel sediments, whereas the barrier island facies include dune, littoral and offshore channel deposits. Thus, each barrier sequence constitutes a formation . The Georgia Sea Islands bordering the mainland are, for the most part, Holocene in age. The Pleistocene deposits are deeply podsolized in marked contrast to the poorly developed soil profiles in the Holocene sediments. Analysis of the heavy mineral fraction of samples from the Pleistocene Formations shows that, despite pedogenesis and diagenesis, there is no apparent relationship between depth of weathering and occurrence of minerals. Distinctive constituents of the Pleistocene barrier island deposits in order of percentage occurrence are sillimanite, staurolite, kyanite, epidote, hornblende, garnet, andalusite and zoisite--a medium to high grade metamorphic suite. Two heavy mineral provinces can be distinguished, based primarily on the epidote and green hornblende content of the Pleistocene and Holocene sediments. These are a Holocene beach province, fairly high in both epidote and green hornblende, and a Pleistocene province low in both minerals. These two provinces are also distinctive with regard to the amount of sillimanite which is far more abundant in Pleistocene, than in Holocene sands. Corroborative evidence has been found in respect of a number of conclusions reached by previous workers. The principal conclusion is that the heavy minerals of the Georgia Coastal Plain appear to have been derived originally from the Georgia Piedmont.

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