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PETROLOGIC AND PETROGRAPHIC ANALYSIS OF THE ALTAMAHA FORMATION IN THE SOPERTON AREA, TREUTLEN COUNTY, GEORGIA **

Abstract

The Miocene Altamaha Formation consists of well-indurated sandstones that crop out infrequently as prominent exposures in the Coastal Plain of Georgia. Bedrock exposures are rare in the Coastal Plain, so the Altamaha is a well-known unit in the area. Surprisingly, only a few brief descriptions of the Altamaha have been published and none include detailed petrographic analysis. Exposures of the Altamaha are abundant in the Soperton, Georgia area. This is due to the hilly nature of the landscape and the sub-horizontal bedding of the sandstone. These exposures do not show the top or bottom of the unit and this makes it difficult to measure the thickness of the sandstone. However, based on the sections that are exposed, the unit is at least 6 meters thick. Outcrop and hand sample analysis shows that the unit is composed primarily of poorly sorted, angular to sub-angular quartz grains with varying degrees of clay matrix. The unit is usually white in color with abundant secondary staining from iron oxides. Grain size ranges from medium sand to pebbly conglomerates. The clay matrix is interpreted to be the result of in situ weathering of feldspar grains. If this interpretation is correct, these sandstones were probably arkosic sands when originally deposited. Samples were collected from seven locations along highway 221 south of Soperton, Georgia, and along highway 46 east of Soperton, Georgia. Select samples were cut and shipped for thin section processing to be further analyzed using a petrographic microscope.

Acknowledgements

VSU Dept of Physics, Astronomy, and Geosciences

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