Does glacial environment produce glacial mineral grains? Pro- and supra-glacial Icelandic sediments in microtextural study

摘要

Mineral grains from proglacial and supraglacial sedimentary settings in central south-eastern Iceland are considered in this study and analysed with the use of scanning electron microscope (SEM) techniques. By applying this, it is attempted to answer the key research question of whether quartz grains that come from a glacial-related sedimentary environment are indeed of glacial origin. The study also attempts to provide a linkage between microtextures produced on coarser and finer grains and to verify whether mineral grains from adjacent cryconite holes are similar or different. The preliminary assumption was that the more intense glacial grain record was based on several glacial activities from more and less recent glacial events in Iceland, and this assumption is true to some extent, because a set of sustained-shear-stress microtextures is found on coarser grains, especially in supraglacial and terminal moraine sediment samples. This latter reveals as much as 9% of glacial-type microtextures and this value seems much lower than in previous studies, which clearly argues for only limited grain glacial transformation. Glacial grains diminish with distance from a glacier, where fluvial grains dominate. Fine-grained cryoconite mineral grains reveal a proportion of glacially-induced microtextures that, nonetheless, may be a result of grain-crushing in the finer fraction. Long-distance-transported grains are practically absent in the finer fraction, likely because they are still too large to be entrained into the atmosphere. Finally, the adjacent neighbouring cryoconite holes reveal a different set of grain types, meaning that every cryoconite hole is independent and its grain type might be very random.