Sandwich-like sandur sedimentation - Markov chain analysis

What is it about?

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). 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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Why is it important?

Conventional sedimentological analysis did not include a statistical approach to the vertical sequence of lithofacies, but now it is clear that Markov chain analysis enables a relatively easy recognition of general regularities in the vertical succession of lithofacies. Due to the large number of data required for successful analysis, the method is usually applied to, for example, studies of lacustrine and glaciolacustrine sediments and alluvial sequences. The considerable diversity and sandwich-like occurrence of glacifluvial sediments require a statistical tool such as Markov chain analysis for a quantitative approach. The aim of the present study is to increase the understanding of the glacial hydrology and depositional mechanism of sandur lithofacies and cycles obtained by Markov chain analysis.