7 I G Implications For Glacial Landsystems

The study of ancient (Pleistocene) glacial landsystems often assumes, albeit implicitly, that component landforms and sediments are in a pristine state. As this chapter has emphasized, this is not always the case, as both may have experienced significant paraglacial modification by non-glacial processes. Depending on the processes involved, the original sediments may be only slightly modified, or altered beyond recognition by selective entrainment or sorting during deposition, potentially leading to misinterpretation of the significance of Quaternary landform assemblages or stratigraphic sequences. Diamictons previously interpreted as in situ till or gelifluctate have been shown to represent paraglacial debris-flow deposits (e.g. Holmes and Street-Perrott, 1989; Wright, 1991; Harris, 1998; Bennett, 1999), and valley-fill gravels originally interpreted as outwash have been shown to have a paraglacial alluvial origin (Jackson et al., 1982). The form of cirques and glacial troughs may be extensively altered after deglaciation by rock-slope failure, rockfall and reworking of drift-mantled slopes (e.g. Bovis, 1990; Ballantyne and Benn, 1994, 1996; Augustinus, 1995a, b; Curry, 1999, 2000a). Individual depositional landforms such as moraines or subglacial bedforms may have experienced paraglacial modification that has altered their surface form and sediment characteristics (e.g. Boulton and Dent, 1974; Rose, 1991; Dardis et al., 1994; Matthews et al., 1998; Etzelmuller, 2000). Few attributes of glacial landsystems are thus immune to significant paraglacial modification. One implication is that the investigation of ancient glacial landsystems requires an understanding not only of the environment and mechanics of orginal sediment deposition by glacier ice or glacial meltwater, but also of the paraglacial processes that may have affected, sometimes substantially, their subsequent modification.

Acknowledgements

The author thanks the following for permission to reproduce published material: the Regents of the University of Colorado (Fig. 17.8); Professor Martin Sharp and the International Glaciological Society (Fig. 17.9); E. Schweizerbart'sche Verlagsbuchhandlung (Fig. 17.10); and Academic Press (Fig. 17.14).

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