2008 Joint Meeting of The Geological Society of America, Soil Science Society of America, American Society of Agronomy, Crop Science Society of America, Gulf Coast Association of Geological Societies with the Gulf Coast Section of SEPM

Paper No. 2
Presentation Time: 8:00 AM-6:00 PM

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

CARVAJAL, Cristian, Energy Technology Company, Chevron, 1500 Louisiana St, Houston, TX 77002 and STEEL, Ronald, Jackson School of Geosciences, University of Texas at Austin, 1 University Station C1100, Austin, TX 78712, ccarvajal@chevron.com

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.