The impact of periglacial processes on Palaeolithic sites: The case of sorted patterned grounds

During the Last Glaciation, Western Europe witnessed recurrent millennial-scale episodes of periglacial climates, that had significant impact on Palaeolithic site preservation. After a review on the genesis and climatic meaning of sorted patterned grounds, examples of polygons, stripes and stone-banked solifluction lobes taken from archaeological contexts are described. Sorted features in Palaeolithic sites imply that caution should be taken in site patterning analysis for reconstructing past human behaviours, since spatial alteration of the original anthropogenic pattern took place. On low gradients, artefact movements remain limited but may increase dramatically on slopes when solifluction adds to sorting processes. Although these features are widespread in modern periglacial environments, archaeological examples remain scarce. Multiple factors are probably involved, including lack of knowledge of periglacial processes and landforms by archaeologists leading to misinterpretation, but also more or less complete obliteration of surface features by sedimentary processes upon burial. However, it is assumed that scarcity of clear anthropogenic patterning in French Palaeolithic sites before the Late Glacial is due for a large part to post-depositional disturbance by periglacial processes.