2014 GSA Annual Meeting in Vancouver, British Columbia (19–22 October 2014)

Paper No. 320-29
Presentation Time: 4:00 PM


HAQUE, Ziaul, Department of Geosciences, Auburn University, 210 Petrie Hall, Auburn, AL 36849, UDDIN, Ashraf, Department of Geosciences, Auburn University, Auburn, AL 36849, HAMES, Willis E., Department of Geology and Geography, Auburn University, 210 Petrie Hall, Auburn, AL 36849 and PASHIN, Jack C., Boone Pickens School of Geology, Oklahoma State University, 105 Noble Research Center, Stillwater, OK 74078

The Cahaba Synclinorium of Alabama contains >2.5 km of Pennsylvanian synorogenic clastic wedge sediment in the Pottsville Formation. The upper 800 m of the formation consists of coarse conglomerate with lesser amounts of sandstone, shale, and coal. Known as the conglomerate measures, this magnafacies was deposited in a series of stacked braidplain-anastomosis cycles, possibly at the distal fringes of giant piedmont fans. Aggradation of widespread bedload-dominated fluvial systems may have led to the development of anastomosed fluvial systems with peatlands, which are represented by thick, low-sulfur coal seams. A total of 36 conglomerate and 10 sandstone samples were collected from cores. Petrographic analysis reveals the source of this coarse-grained, synorogenic sediment.

Clasts within the conglomerate units consist mainly of chert, sedimentary and metamorphic lithoclasts and lesser amount of volcanic lithoclasts. Medium-to-high grade metamorphic lithic fragments are dominant. Carbonate clasts are present, along with large fragments of chert that appear to be derived principally from the Cambrian-Ordovician Knox Group. Both rhyolite and basalt clasts are present in the conglomerate, as are argillaceous lithic fragments. Clast composition indicates a proximal orogenic source that includes elements of the Appalachian thrust belt and the crystalline core of the Appalachians. The low abundance of heavy minerals and abundance of ultra-stable minerals in the upper Pottsville sandstone reflects intense chemical weathering, which is consistent with an equatorial paleolatitude. The presence of rutile and garnet further suggests a medium- to high-grade regionally metamorphosed source in the southern Appalachians. Ongoing research on detrital geochronology and mineral chemistry will provide additional information on provenance of the upper Pottsville Formation.

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