River Landforms and Sediments: Evidence of Climatic Change

Abstract

Changes in the style of fluvial deposits have long been used by sedimentologists as an indication of broad changes in climate. Certainly, in traversing the globe from one environmental extreme to the other — from humid to arid regions — it is possible to discern substantial differences in the character of rivers, both from the point of view of the forms that they adopt and in the sediments that they carry (Schumm 1977, Wolman and Gerson 1978). However, rivers react to a number of stimuli, and it is often difficult to determine whether a change in character reflects tectonic or climatic influences, or both (Fros-tick and Reid 1989a). Attempts to attribute cause inevitably and ingeniously simplify the setting by choosing systems in areas where most factors are presumed to have remained more or less constant while, ideally, another varies monotonically. So, for example, location on a stable craton may allow an assessment of the impacts of climatic change on river systems without the additional complications that arise from tectonic instability (Schumm 1968). However, while this approach may be useful in deducing the response of rivers to recent shifts in climate — say, those of the late Pleistocene and Holocene — and may be instructive in indicating the direction and magnitude of likely changes to be expected in river systems during periods of environmental change, the sedimentary legacies are often too similar to those assumed to arise from tectonic influences to ascribe changes in sedimentary style confidently to either set of causes when stepping further back in time.