Abstract:

Shelf-edge delta depositional style and particularly the presence of river-dominated shelf-edge deltas is a reliable indicator of deep-water sand delivery, as documented by a dataset of some 29 shelf-margin clinoforms. Shelf-edge delta regime, defined as the sum of the effects of fluvial, tidal, wave, and other oceanographic currents impacting deltas as they arrive at the shelf edge is a key predictor for likelihood of sand transport off the shelf edge to deep water. Conventional sequence-stratigraphic concepts assume that delivery of sand to the deep water occurs primarily during falling and lowstand of relative sea level, and that basinward transport is associated with shelf-edge incision and sediment bypass. Recent analysis of outcrop and subsurface datasets has shown that sediment can also be transported to the deep water during rising and highstand of sea level provided sediment flux is high. In addition, some examples with documented shelf-edge entrenchment associated with sea-level fall did not deliver significant sand volumes to the deep water. In contrast to the emphasis given to sea level and supply, the role of the shelf-edge delta itself, and especially its process regime, has received relatively little attention. The data suggest that the behavior and process regime of the delta at the shelf edge is critical, except where shelf width is minimal.

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