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Red Bluff, Marion County, Mississippi: A Citronelle Braided Stream Deposit
Mark L. Smith, Maurice Meylan (1)
Red Bluff is an erosional escarpment located on the western margin of the Pearl River floodplain in northwestern Marion County, Mississippi. The bluff shows approximately 30 meters of relief and is composed of alternating units of sand and sandy gravel, strikingly colored red to yellow. The sand grains are composed primarily of quartz, with small amounts of heavy minerals and feldspar. The gravel is composed of varying percentages of chert, flint, jasper, rip-up clasts, quartz and tripoli, including a small fraction of silicified Paleozoic fossils.
Grain size analysis of the sediment and investigation of the sedimentary structures present suggest a braided-fluvial environment of deposition. Particle sizes in the medium sand to pebble range predominate in all units; very little silt and clay is present. The largest "particles" present are boulder-size rip-up clasts. The most conspicuous sedimentary structures at Red Bluff are graded bedding, low-angle to medium-angle cross-bedding and well-developed paleochannels.
A statistical comparison (discriminant analysis) of the seven most abundant heavy minerals of Red Bluff with the same suite of heavy minerals found at the type section of the Citronelle Formation (Plio-Pleistocene) and outcrops of a known Miocene coarse clastic unit indicates a correlation of Red Bluff to the Citronelle Formation. These heavy minerals are kyanite, staurolite, rutile, tourmaline, zircon, black opaques (primarily ilmenite and magnetite) and white opaques (primarily leucoxene).
The suite of heavy minerals present at Red Bluff belongs to the East Gulf Province. This metamorphic assemblage of heavy minerals implies the source area of the sediments at Red Bluff to be the southern Appalachians. The silicified pebble-size Devonian-Mississippian fossils most likely were derived from formations flanking the southern Appalachians in northern Alabama.
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