11 Undergraduate Research I (Posters)

Thursday, 12 April 2018
8:00 AM - 12:00 PM
Room 301 DE/Henley Concourse

GEOLOGY AND BLUE RIDGE ESCARPMENT EVOLUTION ALONG THE THOMPSON RIVER IN NORTHWESTERN SOUTH CAROLINA AND ADJACENT NORTH CAROLINA

Paper number: 11-15
Program: Theme Sessions
Time: 8:00 AM – 12:00 PM

Authors

Abstract

Understanding river erosional processes is necessary in conceptualizing escarpment evolution and migration. Previously, escarpment evolution was thought to be a process of slow, uniform retreat, but new evidence suggests that the Blue Ridge Escarpment (BRE) experienced episodic and irregular retreat. This research examined the Thompson River in upstate South Carolina and adjacent North Carolina as a case study in order to understand what erosional processes are influencing escarpment retreat along the BRE. Field studies along the Thompson River examined structural and petrologic features of the bedrock. The dominant bedrock is Toxaway Gneiss, and thin section analysis reveals the primary mineralogy to be quartz (20-35%), microcline (30-35%), plagioclase (15-25 %), and biotite (10-15%) with accessory muscovite, epidote, and hornblende. Whole rock chemistry shows a range of silica content from 64 to 78 wt. %, which corroborates well with quartz abundance seen in thin section. A total of 32 joints in bedrock were measured, and the major joint sets have orientations striking primarily NS and EW with nearly vertical dips. A total of 32 foliations in Toxaway Gneiss show that the dominant foliations were striking uniformly NE with a gentle dip to the SE in the direction of river flow, making the Thompson River predominantly a down-dip river. Digital Elevation Models (DEM) and longitudinal profiles reveal one major knickpoint with many intervening down-dip foliation slides and 1-2 meter waterfalls. The Atlantic-draining Thompson River has a watershed area of 29 km2 and flows primarily on bedrock at the bottom of a deep gorge with an average gradient of about 120m/km (620ft/mi). Minor potholes and smooth, polished slide surfaces demonstrate abrasive forces at work. However, intersecting joints and rockfall at the major knickpoint suggest erosional plucking outpaces the abrasive forces as the primary mechanism for headward erosion.

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

doi: 10.1130/abs/2018SE-311517

© Copyright 2018 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.