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Georgia Journal of Science

Article Title

A PETROLOGIC AND PETROGRAPHIC ANALYSIS OF SANDSTONES FROM THE BROXTON ROCKS EXPOSURE, BROXTON, GA

Abstract

The Broxton Rocks are a prominent exposure of well-indurated sandstone assigned to the Miocene Altamaha Formation of the Georgia Coastal Plain. Early workers called this unit the “Altamaha Grit.” The sandstones here form impressive 3-10 m high vertical cliffs on either side of a small valley formed by Rocky Creek. The cliffs consist of multiple beds of sandstone 0.5 to 1.5 m thick. Some layers contain abundant granules and pebbles of quartz, and some layers show vague cross-bedding. No obvious channels were observed. Similar exposures of the Altamaha Formation occur elsewhere in Georgia, including a series of outcrops along I-75 near the Ashburn GA rest stop. Initial petrographic examination reveals these sandstones to be composed primarily of very poorly sorted, highly angular quartz grains with a significant clay matrix (>10%?). Minor quartz overgrowths and some microcline grains were also observed. All of the samples and thin sections display at least some secondary iron-oxide staining. The iron-oxide is locally well-developed and in some places overprints and obscures the original material. A total of ten samples were collected from the Broxton Rocks Preserve north of Broxton, Georgia. These samples will undergo further study including petrographic point counts. The Broxton Rocks Preserve is owned and managed by The Nature Conservancy. We are grateful for their permission to visit the preserve and their assistance with this project.

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