Periglacial sediments: do they exist?
‘Periglacial deposits’ have often been reported in the Quaternary geological literature. Sometimes their identity has been confused with the periglacial processes, landforms and environments with which these deposits are linked. However, the question arises: what are the diagnostic characteristics of such ‘periglacial’ deposits? A number of examples illustrate that ‘periglacial deposition’ follows the general geomorphological and sedimentological laws, although it may be influenced by specific conditions of vegetation and sediment availability. These may be completely or partly dependent on periglacial climatic conditions. Some marginal conditions are specific to cold environments, for instance the scarcity of vegetation that has a clear effect on transport and deposition of aeolian sediments. In addition, the intensity of some processes is governed by climate-derived conditions, for instance in the case of fluvial and slope processes. In this sense, the answer to the question in the title is negative. ‘Periglacial deposits’ do not correspond to any particular sedimentary process. This conclusion is, however, only valid when post-depositional weathering and deformations at micro- and macro-scale are excluded.
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Understanding the sediments deposited by glaciers or other cold-climate processes assumes enhanced significance in the context of current global warming and the predicted melt and retreat of glaciers and ice sheets.
This volume analyses glacial, proglacial and periglacial settings focusing, among others, on sedimentation at termini of tidewater glaciers, on hitherto not-well-understood high-mountain features, and on sediments such as slope and aeolian deposits whose clasts were sourced in glacial and periglacial regions, but have been transported and deposited by azonal processes. Difficulties are thus often encountered in inferring Pleistocene and pre-Pleistocene cold-climate conditions when the sedimentary record lacks many of the specific diagnostic indicators. The main objective of this volume is to establish the validity and limitations of the evidence that can be obtained from widely distributed clastic deposits, in order to achieve reliable palaeogeographic and palaeoclimatic reconstructions. At a more general level and on the much longer geological timescale, an understanding of ice-marginal and periglacial environments may better prepare us for the unavoidable reversal towards cooler and perhaps even glacial times in the future.