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Southeastern Section - 61st Annual Meeting (1–2 April 2012)

Paper No. 2
Presentation Time: 1:30 PM-5:00 PM

CLAST ANALYSIS AND SPATIAL VARIATION OF ALLUVIAL FAN CONGLOMERATES IN THE NEOPROTEROZOIC LOWER MOUNT ROGERS FORMATION, BLUE RIDGE, SW VIRGINIA


JESSEE, Marcus1, MCCLELLAN, Elizabeth1, YONTS, Jason2 and GREGORY, Sarah1, (1)Dept. of Geology, Radford University, P.O. Box 6939, 101 Reed Hall, Radford, VA 24142, (2)Department of Geological Sciences, East Carolina University, 101 Graham Building, Greenville, NC 27858, mjessee3@radford.edu

The Mount Rogers Formation (MRF) in the Blue Ridge province in SW Virginia and adjacent North Carolina formed during a failed rift event involving the Rodinian supercontinent at ~ 760 Ma, that predated successful rifting at ~ 550 Ma. The MRF, which nonconformably overlies Mesoproterozoic basement (the Cranberry Gneiss), is subdivided into two distinct units. The upper MRF constitutes an eruptive center dominated by voluminous rhyolite lavas and ash flow sheets, while the lower MRF contains a bimodal basalt/rhyolite volcanic sequence intermixed with alluvial fan sedimentary deposits. The alluvial fan system is composed of arkosic conglomerates and sandstones that likely represent a progradational sequence formed during synsedimentary faulting. We analyzed the spatial variation of the sedimentary deposits to determine aerial extent, facies variation, and geometry of the alluvial fan deposits. Analytical methods include detailed outcrop mapping, point counting of conglomerates in outcrop, and data interpretation using spatial statistics. Through the implementation of this methodology three distinct subsystems are defined. Subsystem 1 is composed of matrix- to clast-supported conglomerates with matrix/clast ratio of < 1 and clast size commonly > 10 cm in diameter. Conglomerates are polymict, but rhyolite clasts dominate and make up > 50 percent of the total outcrop. Subsystem 2 comprises polymict matrix-supported conglomerate with matrix/clast ratio > 1, and clasts size typically < 10 cm in diameter; rhyolite is again the dominant clast type, but makes up < 50 percent of the total outcrop. Subsystem 3 is composed of pebbly metasandstone with scattered pebble-sized clasts, predominately of vein quartz. The subsystems are interpreted to represent proximal, midfan, and distal facies, respectively, and their spatial distribution, both along and across strike, aids in reconstructing the original fan geometry.

Session No. 13--Booth# 2

T1. Terranes of the Southern Appalachian Blue Ridge and Piedmont: Insights Into Their Tectonic Heritage and Incorporation Into the Orogen From Recent Geochronologic, Isotopic, Provenance, and Field Studies (Posters)
Sunday, 1 April 2012: 1:30 PM-5:00 PM
Grand Ballroom (Marriott Rennaissance)
Geological Society of America Abstracts with Programs. Vol. 44, No. 4, p.29
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