SEDIMENT SUPPLY AND CLIMATE-CHANGE - IMPLICATIONS FOR BASIN STRATIGRAPHY

The rate of sediment supply from erosional catchment to depositional b asin depends primarily upon climate, relief, catchment slope and litho logy. It varies in both time and space. Spatial changes in erosion rat es due to variations in lithology are illustrated by contrasting rates of drainage divide migration away from faults of known ages. Time var iations in relative sediment supply are extremely complex and vary wid ely according to the direction and magnitude of climate change. In man y parts of the Great Basin and south-western USA, glacial maximum clim ates were characterized by higher effective moisture and the altitudin al downward spread of woods and forests. Sparse data from alluvial fan s indicate reduced sediment supply, despite the increased runoff evide nt from higher lake levels. The situation in Mediterranean areas is le ss clear, with rival climatic scenarios for vegetation ecotypes predic ting contrasting runoff. In order to test these latter we run Cumulati ve Seasonal Erosion Potential [CSEP] experiments for present-day and a variety of full-glacial Mediterranean candidate climates. The results indicate the likelihood of enhanced sediment supply and runoff compar ed to the present day during full-glacial times for a cool wet winter climate and a reduction in sediment supply and runoff for a full-glaci al cool dry winter climate. We then explore the consequences of such p hase differences in sediment supply, and sea and lake levels for the s tratigraphy of sedimentary basins. Highstands and lowstands of sea or lake may be accompanied by greater or lesser sediment and water supply , as determined by the regional climate and the direction of climatic change. Thus marine lowstands are not necessarily periods of great tra nsfer of coarse elastic sediments to shelves and deep water basinal en vironments. Unsteady sediment supply has greatest implications for all uvial systems, in particular the effect that changing relative supplie s of water and sediment have upon river and fan channel incision.