The surface textures of almost 1300 quartz grains in the 0.8-1.0 mm and 0.5-0.8 mm size fractions were studied in order to analyse the effects of frost weathering. Some grains had undergone periglacial processes in present-day active layers in Canada, Spitsbergen and Mongolia, whereas other grains were sampled from a former active layer in Poland. Microstructures were studied under a scanning electron microscope and the results statistically analysed in order to distinguish characteristic microstructures resulting from frost weathering. The quartz grains with these microstructures had been deposited by fluvial, aeolian and glacial processes and their characteristic microstructures are classified as primary microstructures. Microstructures that developed on primary ones as a result of frost weathering are called secondary microstructures. The most characteristic secondary frost weathering microstructures on the quartz grains are (1) small breakage blocks (<10 μm), (2) big breakage blocks (>10 μm) and (3) single small conchoidal fractures (<10 μm). These secondary microstructures developed commonly on the following primary microstructures: (1) sharp edges of big conchoidal fractures (>10 μm), (2) microsteps, (3) edge roundings and (4) crescentic gouges. These findings facilitate the reconstruction of cryogenic conditions, support the recognition of ancient active layers and indicate grains that are particularly susceptible to frost weathering.

The Drawa sandur, which is the largest, coarse‐grained sandur in Poland, dates from the Pomeranian phase of the Weichselian glaciation (c. 16 ka BP). Using Markov chain analysis we infer that five cycles and five rhythms occur in its proximal part. The cycles dominated by Gt and St lithofacies in the lower part of the sandur succession and by a GDm lithofacies in the upper part, are fining‐upward cycles deposited in braided channels during large ablation floods. Three groups of cycles are distinguished based on their genesis: (i) cycles due to channel‐sheet evolution during large floods; (ii) cycles due to braid‐bar development during initial and advanced diminishing of floods; and (iii) cycles developed in the thalweg or interbar channels. The succession as a whole forms a large‐scale coarsening‐up megacycle (‘sandur megacycle’) which corresponds to a phase of ice‐sheet advance. Because the cyclicity was evident from Markov chain analysis of the sedimentary succession, we suggest that this statistical tool is valuable for reconstruction of glacifluvial sedimentary conditions, particularly as it can shed new light on the palaeogeographical development of sandar.

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