Geology and Evolution of the Blue Ridge Escarpment Along the Toxaway River In Northwestern South Carolina and Adjacent North Carolina Egan G. Jarvis and William A. Ranson Department of Earth and Environmental Science Furman University, Greenville, SC 29613 Introduction Structure Petrology As part of the research we walked the length of the Geomorphology Discussion The effects of river systems on the development of Toxaway River. We collected lithological and structural data Five rock specimens were collected along the Toxaway River. The main lithology is geologic structures has intrigued scientists for including foliation (Figure 2 ) and joints (Figure 3) . This data the Toxaway Gneiss with primary mineralogy of biotite (5-10%), muscovite (10- centuries. The Blue Ridge Escarpment (BRE), which dates Regarding the origin of the Blue Ridge escarpment, one major was then plotted as poles to foliation (Figure 4) and rose 15%), quartz (20-30%), microcline (20-25%), and plagioclase (20-25%) (Figure 6a to the Mesozoic, has recorded a long history of evolution hypothesis proposes that the BRE was initially formed during diagram for joint measurements (Figure 5). and b). which many believe to be the result of fluvial processes the Mesozoic era as a rift-flank uplift (Spotila et al., 2004). Where the Toxaway River transects the Brevard Zone, the major rock type is (Spotilla et al, 2004). This study focused on erosional and Knickpoint formation may be the result of rejuvenation of muscovite schist and phyllite with a mineralogy consisting of plagioclase (15%), fluvial processes that play an influential role in the Appalachian topography associated with Late Cenozoic mantle quartz (40%), muscovite (40%) with 5% accessory biotite, chlorite, and epidote evolution of the BRE, including cavitation, abrasion and dynamics (Hill and Stewart, 2018). The main erosive Tox 4 (Figure 6b, Figure 7a and 7c). plucking. mechanisms by which the Toxaway River erodes the Blue Ridge Escarpment is through plucking and abrasion. Plucking TOX 7 Tox 9 occurs along orthogonal joints in hard Toxaway gneiss whereas abrasion occurs primarily in areas with softer rocks such as phyllonites and schists associated with the Brevard fault zone. Geologic Setting This study corroborates previous studies of other rivers a flowing into Lake Jocassee, including the Whitewater, Thompson, and Horsepasture River, although all rivers have The Blue Ridge Escarpment (BRE) is a 500 km-long geologic GIS foliation map for Figure 2. Figure 3. GIS joint map for the Figure 8a and b. a) Large knickpoint along the Toxaway Creek “ oh hell no” unique characteristics. landform that lies alongside the Eastern Continental Divide. the Toxaway River Toxaway River falls is developed through fluvial processes. (approximately 120 ft vertical For the last 180 million years the BRE has acted as an drop) b) Cascade style Wintergreen falls. Each demonstrates a different type asymmetrical drainage divide between the eastern flowing of knickpoint. streams that empty into the Atlantic and western streams that flow into the Gulf of Mexico (Prince et al. 2010). Because of b this asymmetrical divide, the BRE has been a structure that has References been defined by erosional retreat. Even though the BRE is Fig 6a and b. a) Well jointed outcrop of stiped Toxaway Gneiss. b) Rock very old, it still maintains a high level of relief, from the is more schist like and softer which allows for the development of Spotila, J.A., Buscher, J.T., Meigs, A.J. , Reiners, P.W., Blue Ridge uplands to the Piedmont (Miller et al. repeated potholes. An outcrop of muscovite schist and phyllite showing 2004, Long-term glacial erosion of active mountain belts: Example of the Chugach–St. Elias Range, Alaska, Geology, v.32 ,no.6, p.501–504. 2013). The BRE in northwestern South Carolina and adjacent the development of abundant potholes . Prince, P.S., Spotila, J.A., Henika, W.S., 2010, New North Carolina lies within the Inner Piedmont of the Tugaloo physical evidence of the role of stream capture in active retreat of the Blue Ridge Terrane and just east of the Brevard Zone and the Eastern escarpment, southern Appalachians: Geomorphology, 123, p. 305-319 Miller, S.R., Sak, P.B., Kirby, E., Bierman, P.R., 2013, Blue Ridge. Neogene rejuvenation of central Appalachian topography: Evidence for differential rock uplift from stream profiles and erosion rates: Earth and Planetary Science letters, 369-370, p.1-12. Hatcher, R.D., Tollo, R.P., Bartholomew, M.J., Hibbard ,J.P., Karabinos, P.M., 2010, The Appalachian Orogen; a brief summary (in From Rodinia to Pangea; the lithotctonic record of the Appalachian region), Figure 4a and 4b. a) A stereonet of poles to foliation with the majority Geological Society of America, 206: 1-19 . striking to the NE and dipping to the SE. b) A Rose diagram showing the Hill, J.S, and Stewart, K.G, 2018, The Boone fault and its Figure 9) Potholes formed in muscovite schist and implications for Cenozoic topographic rejuvenation of the southern Appalachian distribution of joint orientations along the Toxaway River. Mountains: Carolina Geological society, v.79, p. 95-107 phyllite due to abrasion along the Toxaway River, ranging in size from 15 cm to 1 m. Figure 5:. The repetition of a b a) Digital elevation orthogonal joints along the Figure 10a and b. a model of the Toxaway River. The Acknowledgments Toxaway River, particularly at watershed for the Toxaway River as knickpoint faces, increases the delineate in the DEM is 46.73 square likelihood of mechanical processes I would like to thank Dr. Ranson. His boundless leadership miles (380.0 km2) with a length of 21.31 like plucking. and encouragement, allowed me to do something that in the mi (34.30 km). b Longitudinal profile of Figure 1. Location map of Lake Jocassee. . ) start I thought I would procrastinate more on. Thank you to the Toxaway River showing knickpoints. The Southern Appalachian's have undergone several orogenic c Furman University and the Furman Advantage for events: The first orogenic event was the Ordovician Taconic providing the funding for this research. orogeny, which involved arc accretion; the second was the Figure 7a, b and c. Photomicrographs of thin sections of rock samples taken Acadian–Neoacadian orogeny, which involved the accretion of in cross-polarized light. a) Tox 7, phyllite schist with biotite, muscovite, the Carolina superterrane (Hatcher et al. 2010); the quartz, microcline, and plagioclase with dextral sheer. b) Tox 8, Toxaway Alleghenian orogeny, during which Gondwana collided with Gneiss with quartz, plagioclase porphyroblasts , biotite, muscovite. c) Tox 3, Laurentia to form Pangea. The primary bedrock associated phyllite schist with microcline, quartz , plagioclase, muscovite and biotite b with the Toxaway River is Toxaway Gneiss, Chauga River schist, and the Tallulah Falls formation .