COMPARATIVE SEM ANALYSIS OF QUARTZ MICROTEXTURES IN FLUVIAL SAND FROM TROPICAL, ARID, AND PROGLACIAL SYSTEMS: A POSSIBLE CLIMATE PROXY

Numerous studies of quartz microtextures using scanning electron microscopy (SEM) have been performed as means to asses paleoenvironmental influences on clastic sediments, and many have found correlations between paleoenvironment and certain suites of textures. However, using these microtextures as a viable paleoclimatic indicator requires quantitative verification of 1) microtextural occurrence in modern systems, and 2) persistence of these textures with distance of fluvial transport. This research is an attempt to fill a gap in quartz microtextural studies by systematically documenting quartz microtextures from modern fluvial systems in various climate settings but controlled, as much as possible, for parent lithology, and drainage-basin attributes (basin size, relief, and fluvial transport distance). First-cycle quartz sand samples were collected along ~15 km transects from fluvial systems in a hot-humid (Puerto Rico), hot-arid (Anza Borrego, CA), and cold-humid proglacial (Norway) systems. The source rocks for each of the three systems were coarse-grained granitoids, with auxiliary coarse-grained metamorphic rocks in Norway. Results from statistical analysis reveal trends in textural assemblages. Proglacial samples had a higher occurrence of high-stress based textures relative to the non-glacial samples such as straight and curved grooves, troughs, and crescentic gouges. The tropical samples contained a higher percentage of chemical textures relative to the non-tropical samples such as clay coatings, dissolution etching, and preweathered surfaces. In all of the samples, the occurrence of percussion based textures increased as the samples proceeded through the fluvial system and proximal textures were still present in more distal samples.