Paleozoic history of the Nantahala and Brasstown formations of the basal Murphy belt, southwesternmost North Carolina and northernmost Georgia

• Other Authors: Aylor, Joseph Garnett, Jr.
• Format: Others
• Language: English
• Subjects: Geology
• Online Access: http://purl.flvc.org/fsu/lib/digcoll/etd/3088474

The Murphy belt of Georgia and North Carolina is located in the western Blue Ridge of the southern Appalachians. The general structure is a first generation, northeast trending, isoclinal synclinorium, overturned to the northwest. Coaxial second generation folds and oblique third generation folds produce interference patterns. The siliciclastics rocks, which form the basal units in the Murphy belt (Nantahala and Brasstown Formations), are overlain stratigraphically by the Murphy Marble. These three formations make up the Hiwassee River Group. The Nantahala Formation was conformably deposited upon the Great Smoky Group of the Ocoee Supergroup, and the Mineral Bluff Group was unconformably deposited upon the Murphy Marble and underlying units. Subarkosic metasandstones of the Nantahala Formation are composed of recrystallized quartz, detrital feldspar, micas and tourmaline. Nantahala Formation metasiltstones consist of alternating laminations of light-colored, fine-grained subarkosic metasandstone and dark-colored, graphitic metasiltstone containing biotite, garnet, and pyrrhotite. The Brasstown Formation consists of interlayered, dark-colored metapelite, alternating with quartz-rich mica schist, and contains biotite, garnet, and locally staurolite porphyroblasts and detrital feldspar. === These rocks were polydeformed and were metamorphosed up to staurolite grade, but many primary structures are preserved. Planar-tabular cross bedding, asymmetric ripple marks, penecontemporaneous contortion, rip-up clasts, and conglomerate were identified. Progradational relative sea-level cycles as reflected in the Nantahala Formation are associated with the deposition of numerous metasandstone units. These stacked units coarsen upward from metasiltstone into metaconglomerate. Progradational facies were overlain by a transgressive facies represented by the Brasstown Formation, followed by a starved shelf environment during a highstand as represented by the Murphy Marble. === Although direct correlation is complicated by numerous faults, the Early Cambrian Chilhowee Group, overlain by the Shady Dolomite, in the western boundary of the Blue Ridge is probably correlative to the Hiwassee River Group. From Georgia the Hiwassee River Group thickens along strike to the northeast and may be an easterly extension of the Chilhowee Group depositional basin. The fluvial to shallow marine, transgressive Chilhowee Group units were deposited during the initial drift phase in the formation of the Iapetus Ocean on the Atlantic-type Laurentian margin. Hiwassee River Group rocks were probably distal facies equivalents of the Chilhowee Group and were deposited in a middle-shelf environment. === Source: Dissertation Abstracts International, Volume: 55-09, Section: B, page: 3778. === Major Professor: James F. Tull. === Thesis (Ph.D.)--The Florida State University, 1994.