Influence of Rivers, Waves and Tides on Shelf-Edge Delta Architecture and Sand by-Pass to Deep-Water

We document river, wave and tidal processes on shelf-edge deltas and estuaries and investigate the role of these processes on a shelf-margin's architecture and ability to by-pass sand to deep-water areas under differing relative sea level and sediment supply scenarios. In the Lewis-Fox Hills shelf margin (S. Wyoming, Maastrichtian) we integrate well-logs (~500) and outcrops to characterize two depositional cycles at a basin scale. In Clinothem 09, isopach maps and log character indicate that rivers supplied sand to slope canyons to form two sandy deep-water lobes (combined sandstone volume ~ 48 km3). Outcrops distant to the river mouths along the shoreline exhibit storm-wave-generated deltaic facies capped by tide-influenced estuarine deposits, which did not produce significant turbidite successions. Instead, paleocurrents and a shelf-edge sandstone belt indicate that the storm-wave/tidal regime produced an along shore drift that stored sand along the shelf edge, and perhaps fed sand to canyon heads when intersecting river mouths. The storm-wave deltas are aggradational (>50 m) and lack incised valleys, indicating rising relative sea level conditions, and likely a high sediment supply for deltas to reach the shelf edge, aggrade there and supply sand to deep-water areas.

Clinothem 10 shows one large deep-water sand lobe (sandstone volume ~ 53 km3)that correlates to river channel deposits in shelf-edge deltas. These deltas lack a thick wave-dominated sandstone belt at the shelf edge; instead their mouth bar is relatively thin and dominated by flat laminated sandstones (hyperpycnal flows?) that transition to heterolithic, tidally-influenced facies. Fluvial erosion is prominent forming a several 10's kms container, filled by thick fluvial deposits and estuarine strata, which indicate incised valley development and a relative sea level fall. Such incised coastal physiography probably segmented littoral drifts diminishing wave influence, while providing confined areas for tidal amplification and for efficient downslope sand delivery.