The kinematics of ancient tidewater ice margins: criteria for recognition from grounding-line moraines
Ida Lønne, W. Nemec, 2011. "The kinematics of ancient tidewater ice margins: criteria for recognition from grounding-line moraines", Ice-Marginal and Periglacial Processes and Sediments, I. P. Martini, H. M. French, A. PéRez Alberti
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Modern studies indicate that the kinematic behaviour of tidewater glaciers is a crucial part of ice-sheet dynamics. A similar relationship may be expected for ancient ice sheets, but can the kinematics of ancient tidewater ice margins be recognized? The paper addresses this methodological issue by pointing to the high-resolution stratigraphic record of marine moraines, thus far little explored. On the basis of a series of case studies, a range of field criteria are proposed for the recognition of short-term grounding-line movement and possible oscillations in moraine outcrop sections. The method combines allostratigraphic mapping and architectural facies analysis of the moraine sedimentary units formed during glacier advance, subaqueous stillstand and eventual subaerial stillstand, with recognition of the successive ice-contact surfaces. The stacking architecture of the sedimentary units and their ice-contact bounding surfaces reveal the time–distance trajectory of the grounding-line positions. It is also possible to recognize changes in the mode and rate of subglacial sediment delivery, as well as fluctuations in the ice flux and meltwater discharge. This methodology invites detailed studies of marine moraines. Systematic case studies on a regional scale may provide new information on the behaviour of tidewater ice margins and lead to unprecedented insights into the dynamics of ancient ice sheets.
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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.