Deciphering procedure

As a first step in the deciphering procedure, swarms are spatially delineated and classified (Plate 38.9) according to the morphological criteria described above.

Where swarms cross-cut, relative chronologies are established, using striae and till fabric, as well as cross-cutting glacial lin-eations. The swarms are locally sorted into relative-age stacks, according to the relative chronologies, with the first result being the reconstruction of the deglacial envelope. Event swarms and fragments of old deglacial envelopes are then aggregated into groups forming glaciologically plausible, coherent flow patterns. For the reconstruction of time-slice flow patterns, the deglacial envelope is deconvoluted in terms of the changing ice sheet configurations during the deglaciation. This is done by going up-swarm and relating successively younger parts of the swarm to successively younger dispersal centre locations.

The time-slices are distributed into stadials on the basis of correlations with stratigraphical sequences of regional significance. Of particular use in this context are dated interstadial/interglacial sequences bracketing individual glacial sediment units that can be directly correlated to specific swarms. Examples of such glacial sediment units are glaciofluvial deposits (e.g., in eskers forming part of a deglaciation swarm), and till beds that have till fabric directions that can be directionally correlated with glacial lin-eations (drumlins, flutes) in a swarm.

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