21 D13. Petrology, Structure, and Tectonics

Friday, 13 April 2018
8:00 AM - 12:00 PM
Room 300 C

FOSSILS RECOVERED FROM ROCKS CURRENTLY ASSIGNED TO THE NEOPROTEROZOIC WALDEN CREEK GROUP IN THE EPPERSON SYNCLINORIUM OF THE APPALACHIAN WESTERN BLUE RIDGE, GEORGIA AND TENNESSEE, CALL FOR STRATIGRAPHIC REASSIGNMENT

Paper number: 21-1
Program: Technical Sessions
Time: 8:00 AM – 8:20 AM

Authors

Abstract

At its widest extent, near the TN, NC, and GA junction, the S. Appalachian W. Blue Ridge (WBR) is a composite metamorphic allochthon comprised of three major thrust sheets. These rocks have traditionally been interpreted as part of the Neoproterozoic-Cambrian rift-to-drift sequence, and to have reached peak metamorphism during the Ordovician Taconic orogeny. The basal (Great Smoky) thrust sheet structurally overlies the foreland thrust belt and contains rocks assigned to the Neoproterozoic Walden Creek Gp. (WCG), overlain by the lower Cambrian Chilhowee Gp. (CG). The intermediate (Maggies Mill/Citico) thrust sheet is composed of the middle Paleozoic (Silurian–Mississippian(?)) Maggies Mill Formation (MMF) that has no upper stratigraphic constraints, therefore making it difficult to correlate to the surrounding region. Until recently, the MMF was assigned to the WCG based on a distinctive set of lithofacies and lack of paleontologic control. Conodonts and other fossils recently recovered from carbonate rocks in the MMF however, have since resulted in a stratigraphic reassignment of this sequence. The uppermost and main mass of the WBR, floored by the Alaculsy Valley/Miller Cove fault, contains rocks within the Epperson (ES) and Murphy synclines, which importantly are flanked by the Nantahala and Brasstown Formations (NBF), correlated with the Chilhowee Group in the lower thrust sheet. On the SE flank of the ES, the Neoproterozoic Ocoee Supergroup grades upward into the NBF, which is separated from stratigraphically overlying rocks by a regional low-angle unconformity. These younger rocks, nested in the core of the ES, were also assigned to the Neoproterozoic WCG, but contain similar distinctive lithofacies to those in the MMF. In addition, recent paleontologic discoveries from carbonate breccias in the younger ES sequence, paired with structural and stratigraphic constraints, suggest that these rocks are part of a younger (middle Paleozoic?) successor basin, possibly equivalent to the MMF. Through petrographic analysis and microfossil separation we have identified potential fossil fragments, including echinoderm and trilobite fragments, other shelly material, and probable conodont elements. These discoveries call for a revised depositional and tectonic model for this region of the WBR.

Geological Society of America Abstracts with Programs. Vol. 50, No. 3

doi: 10.1130/abs/2018SE-311776

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