Thursday, October 27, 2016

Highlights—Quartz (hamster?) Transport and Surface Microtextures

Although provenance plays a fundamental role in establishing sandstone mineralogy, transport processes impact the sediment as well. To explore the potential utility of transport-associated microtextures, Sweet and Brannan analyze the abundance of glacially and fluvially induced microtextures to assess the role of fluvial overprint on glacially modified grains along ~188 km of the proglacial Chitina River, SE Alaska.  The analysis of SEM observations documents the relative proportions of glacially induced stylus microtextures (i.e., grooves, troughs, and gouges) and fluvial percussion-induced microtextures (i.e., v-shaped cracks and edge rounding) on quartz grain surfaces, and compares how this ratio changes with distance downstream. The results indicate that the glacially induced microtextures input to the river persist downstream, but are modified progressively by traction and saltation. This type of analysis could be applied to ancient fluvial strata provide insights to 1) differentiate between proglacial and nonglacial braided rivers and 2) reconstruct proglacial paleogeography from ancient strata. Furthermore, the results clearly show that it makes a difference how you roll.

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