The vast majority of all sediment is derived from hillslopes. Attempts to understand what controls variability in the sedimentary record should therefore consider the primary variability of hillslope sediment yield to depositional basins. But our understanding of controls on sedimentation, particularly climatic controls, is limited by poor understanding of the links between hillslopes and depositional systems. This is partly because the applications of geomorphic research to sedimentology are not fully realized. The long-term hillslope stratigraphic records of this study provide a crucial physical link between hillslope sediment sources and depositional basins, and between geomorphology and sedimentology.
We compare rare Neogene colluvium and buried hillslopes preserved in superproximal basin-fill exposures to their Quaternary and modern equivalents in two tectonically quiescent basins in southeastern Nevada. Field and laboratory geomorphic and sedimentologic methods are employed to document the provenance of proximal basin sediment, the character and relative amount of sediment produced on local hillslopes at different times, the hillslope weathering and transport processes occurring through time, and the role that rock-type differences have played.
Physical weathering processes have dominated the production of angular, pebbly colluvium on both ancient and modern slopes, and overland flow has been the main process transporting detritus off slopes. Although hillslope processes and products in the study area remained the same in upper Miocene, Pliocene, Pleistocene, and modern records, process rates have varied greatly, indicating that orbital-scale climatic cyclicity can be, but is not always, well expressed in the stratigraphy of continental basins. The vast majority of basin sediment in the study area is derived from hillslopes underlain by volcanic rather than carbonate bedrock, and rock type is the dominant control on sediment yield and landscape development in this tectonically inactive, dry setting.