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Most data about fossil cryogenic phenomena relates to the Late Pleistocene, slightly less to the Middle Pleistocene. In this time interval continental icesheets were less extended than earlier, permafrost zones spread in most regions, however. Thus the presence of a particular cryogenic phase within the Pleistocene was established (Velichko 1973). This is connected with the strongest cooling periods during the Quaternary. Study of past cryogenic features has a practical side as well. Extant landforms on loess areas often may only be explained with active cryogenic processes preceding loess deposition. 相似文献
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