Sediment Supply to the Shelf Margin and Beyond: Alluvial Valley Responses to Sea-Level Change
Michael D. Blum, 2013. "Sediment Supply to the Shelf Margin and Beyond: Alluvial Valley Responses to Sea-Level Change", Shelf Margin Deltas and Linked Down Slope Petroleum Systems–Global Significance and Future Exploration Potential, Harry H. Roberts, Norman C. Rosen, Richard H. Fillon, John B. Anderson
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Shelf-margin deltas and linked downslope depositional systems are in most cases fed by alluvial valleys that serve to deliver sediment eroded from the hinterland. Accordingly, alluvial valleys provide the link between processes that control sediment flux to the continental margin and processes that control dispersal into the basin. Current research shows the volume of sediment delivered to the margin will reflect hinterland drainage areas and large-scale relief. Superimposed on this background rate will be an unsteadiness that reflects climate change in hinterland source regions, but the rates and directions of change in sediment supply will vary regionally. Alluvial valleys modulate unsteadiness in sediment supply through changes in sediment storage. However, regional variability in the rates and directions of change in sediment supply insures that responses to climate change are regionally circumscribed, and alluvial valley systems in different regions may respond in opposite ways to the same global climate change. Sea-level change has little effect on the total volume of sediment delivered to the margin, but instead forces channel extension and shortening, which plays a major role in determining the proximal to distal location of the river mouth point source through which sediment is dispersed to the shelf and beyond. Moreover, the widely used concept of incision and complete sediment bypass within incised valley systems during periods of relative sea-level fall should be abandoned. Instead, falling stage to lowstand fluvial deposition is actually common in well-studied Quaternary analog systems, and falling stage sand bodies may comprise a significant proportion of reservoir-quality sands within many incised valley fill depositional sequences. Models for falling stage and lowstand systems tracts should therefore incorporate significant fluvial channel belt deposits that are likely connected to, and feeding, the offlapping shore faces, shelf-margin deltas, and linked downslope systems.