The rounding and frosting of quartz grains in ice-marginal valley and sandur

What is it about?

This study was carried out in order (1) to trace thesource(s) of the sandur deposits and ice-marginal valey de-posits, (2) to evaluate the role of the proglacial (san-dur) and extraglacial (non-glacial) streams feeding the ice-marginal valey, (3) to specify the reworking and weath-ering processes that affected the quartz grains dur-ing transport, and (4) to consider the influence of the fast aggradation of the sandurs and in the ice-marginal valey on the development of aeolian traces on the quartz grains.

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Why is it important?

The rounding and frosting of quartz grains from the Pomeranian sandurs and the Toruń-Eberswalde ice-marginal valley sediments are the same. In both the sandurs and the ice-marginal valley , very well to moderately rounded and shiny quartz grains prevail; they have a fluvial origin, but the rounding is slightly better in the ice-marginal valley. The fluvial quartz grains in the sandur sediments were probably eroded from sediments in the East Central Baltic, whereas the fluvial quartz grains in the ice-marginal valley were supplied by streams running over the sandurs, or they were eroded from older terrace sediments. The sediments of the Pomeranian sandurs and the Toruń-Eberswalde ice-marginal valley terrace under study contain a small amount of aeolian quartz grains. This must be ascribed to the short duration of the aeolian activity in the front of the Pomera-nian ice sheet, which left insufficient time for changing the micromorphology of the quartz grains; an alternative explanation is that trans-port of particles by rivers from the south (from the extraglacial zone) to the ice-marginal valley was restricted by pre-Pomeranian ice-marginal valley. These older ice-marginal valleys were situated parallel to the Toruń-Eberswalde ice-marginal valley , and could capture the sedimentary particles transported by rivers from the south. Moreover the climate deterioration during the Last Glacial Maximum led to a decrease in the dis-charge of extraglacial rivers to the Toruń-Eberswalde ice-marginal valley .