LAUSR

Abstract The micromorphology of quartz grains in a sedimentary environment is determined by the transport mechanism and the nature of weathering. Both these aspects change during the transport history of grains. Thus important questions include how are quartz grains affected by possible changes in the transport medium, and how quickly do the different micromorphological features develop or disappear. The main goal of this study was to characterize the changes in the micromorphological features of quartz grains during the transition from a glacial to a glaciofluvial environment, and to identify a set of diagnostic microtextures that can be used to distinguish between glacial and glaciofluvial quartz grains. The samples came from the moraines of the Bertilbreen and Horbyebreen glaciers (Svalbard) and from the sediments of glacier-fed rivers in the forelands of these glaciers. A total of 30 different micromorphological features was observed on 800 different quartz grains from 13 samples of glaciofluvial sediment and 3 samples of glacial sediment. It was found that the frequency of rounded grains, V-shaped pits, meandering ridges and cemented microblocks on glaciofluvial grains increased significantly with increasing length of fluvial transport, whereas the frequency of angular grains, straight steps, straight and curved grooves, adhering particles, pitting and oriented etch pits decreased significantly. Different types of micromorphological features of quartz grains change with fluvial transport at different rates. Adhering particles (after the first kilometer of fluvial transport), straight steps and meandering ridges (after the second kilometer of fluvial transport), and V-shape pits, angular shape and straight grooves (after the third kilometer of fluvial transport) are reliable mechanical micromorphological features for distinguishing between glacial and glaciofluvial quartz grains.