AAPG Annual Convention and Exhibition

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Insights Into the Linked Dynamics of Channel Networks on Shelf-Edge Deltas and Submarine Slopes From Physical Experiments and High-Resolution Seismic Data

Abstract

Continental margin deposits provide the most complete record on Earth of paleo-landscapes and paleo-landscape dynamics, in addition to hosting water and hydrocarbon reservoirs. As a result of high Holocene sea-level rise rates, most modern deltas are far from the continental shelf-edge, making it difficult to study sediment routing past coastlines and into the deep ocean in real time. Motivated by observations from acoustically–imaged shelf-edge deltaic systems offshore Brunei and in the Gulf of Mexico, we use physical experiments to explore the key boundary conditions that affect the dynamics of sub-aqueous slope channels linked to deltaic channels. We will discuss how: a) the ratio of sediment discharge to water discharge (Q s:Q w), b) the fraction of coarse sediment in the input grain-size distribution in the basin, c) shoreline shape of shelf-edge deltas and d) delta top-set area affect the volume and spatial extent of sediment deposition on the slope as well as the longevity of sub-aqueous slope channels. In a high Q s:Q w ratio experiment with a uni-modal grain size distribution in the silt regime, delta-top flow was sheet-like and highly mobile, shorelines were smooth and arcuate, subaqueous channels were transient and poorly defined, and slope sedimentation was diffuse. In contrast, in a low Q s:Q w ratio experiment, with a bimodal grain size distribution (one part by weight sand to 9 parts silt), delta top flow was channelized and less mobile, shore-lines were rugose, slope channels were well-defined and persistent through time and deposition on the slope occurred along restricted fairways.