H31I-1549
CLAY MINERALOGY OF AN ALLUVIAL AQUIFER IN A MOUNTAINOUS, SEMIARID TERRAIN, AN EXAMPLE FROM RIFLE, COLORADO
Wednesday, 16 December 2015
Poster Hall (Moscone South)
W Crawford Elliott1, David Lim2, Laura K Zaunbrecher1, Rebecca A Pickering1, Kenneth Hurst Williams3, Alexis Navarre-Sitchler4, Philip E Long5, Vincent Noel6 and John Bargar7, (1)Georgia State University, Atlanta, GA, United States, (2)University of Wisconsin Madison, Department of Geology and Geophysics, Madison, WI, United States, (3)Lawrence Berkeley National Laboratory, Earth Science Divission, Berkeley, CA, United States, (4)Colorado School of Mines, Golden, CO, United States, (5)Lawrence Berkeley National Lab, Chelan, WA, United States, (6)SLAC National Accelerator Laboratory, Menlo Park, CA, United States, (7)Stanford University, Los Altos Hills, CA, United States
Abstract:
Alluvial sediments deposited along the Colorado River corridor in the semi-arid regions of central to western Colorado can be important hosts for legacy contamination including U, V, As and Se. These alluvial sediments host aquifers which are thought to provide important “hot spots” and “hot moments” for microbiological activity controlling organic carbon processing and fluxes in the subsurface. Relatively little is known about the clay mineralogy of these alluvial aquifers and the parent alluvial sediments in spite of the fact that they commonly include lenses of silt-clay materials. These lenses are typically more reduced than coarser grained materials, but zones of reduced and more oxidized materials are present in these alluvial aquifer sediments. The clay mineralogy of the non-reduced parent alluvial sediments of the alluvial aquifer located in Rifle, CO (USA) is composed of chlorite, smectite, illite, kaolinite and quartz. The clay mineralogy of non-reduced fine-grained materials at Rifle are composed of the same suite of minerals found in the sediments plus a vermiculite-smectite intergrade that occurs near the bottom of the aquifer near the top of the Wasatch Formation. The clay mineral assemblages of the system reflect the mineralogically immature character of the source sediments. These assemblages are consistent with sediments and soils that formed in a moderately low rainfall climate and suggestive of minimal transport of the alluvial sediments from their source areas. Chlorite, smectite, smectite-vermiculite intergrade, and illite are the likely phases involved in the sorption of organic carbon and related microbial redox transformations of metals in these sediments. Both the occurrence and abundance of chlorite, smectite-vermiculite, illite and smectite can therefore exert an important control on the contaminant fluxes and are important determinants of biogeofacies in mountainous, semiarid terrains.
