Effect of Weathering on Abrasion of Granitic Gravel, Colorado River (Texas)

Abstract

Research Article| January 01, 1970 Effect of Weathering on Abrasion of Granitic Gravel, Colorado River (Texas) WILLIAM C BRADLEY WILLIAM C BRADLEY Department of Geological Sciences, University of Colorado, Boulder, Colorado 80302 Search for other works by this author on: GSW Google Scholar GSA Bulletin (1970) 81 (1): 61–80. https://doi.org/10.1130/0016-7606(1970)81[61:EOWOAO]2.0.CO;2 Article history received: 09 Apr 1969 rev-recd: 08 Jul 1969 first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation WILLIAM C BRADLEY; Effect of Weathering on Abrasion of Granitic Gravel, Colorado River (Texas). GSA Bulletin 1970;; 81 (1): 61–80. doi: https://doi.org/10.1130/0016-7606(1970)81[61:EOWOAO]2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Precambnan outcrops in the Llano Uplift of central Texas furnish the Colorado River with a distinctive granitic load which changes systematically as it moves downstream. In 160 miles between Austin and the Columbus-Eagle Lake area, coarse granitic gravel diminishes in size by about 50 percent and changes from a dommantly granite-gneissaplite assemblage to a dominantly pegmatite-graphic granite assemblage. Coarse quartz and chert gravel diminish in size by about 30 percent and 20 percent, respectively. In this reach, the Colorado flows on a flood plain whose alluvial width and depth stay fairly constant, a situation unfavorable for significant down-valley sorting (Mackin, 1963). Field observations generally lead to the same conclusion.Abrasion and its relationship to weathering was studied by running fresh and weathered specimens of Colorado River granitic gravel in a Kuenen-type abrasion tank at the University of Texas. Degree of weathering was slight to moderate, with biotite and feldspar the primary and secondary targets. Abrasion of fresh granitic gravel during 160 miles of travel produced only a 10 percent reduction in size. Abrasion of weathered gravel produced a reduction of more than 50 percent and was clearly related to lithology; the biotite-bearing rocks (granite, gneiss, and some aplite) were the least durable, the biotite-free rocks (pegmatite and graphic granite) most durable. Abrasion of quartz and chert produced a reduction in size of less than 10 percent.Changes in size and lithology of coarse granitic gravel along the lower Colorado River are best explained by abrasion of particles tha t weather slightly during periods of temporary alluvial storage. Reduction in size of quartz and chert are not satisfactorily explained for the reach between Austin and Columbus-Eagle Lake, but downstream from Eagle Lake, sorting appears to be in control. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.