(1) Exxon Production Research Co, Houston, TX
(2) Exxon Production Research Co
Abstract: The effects of gradient changes on deep-water depositional systems: An integrated approach
The rheology and concentration of sediment gravity flows strongly affect deposition, location, and style. Rate and magnitude of gradient changes also fundamentally affect depositional response. Since deep-water flows are gravity driven, small topographic changes affect the momentum of individual flows. recent analysis of high-quality 2D and 3D Pleistocene data sets from several basins around the world documents the prominent role seafloor gradient plays on depositional patterns.
In each studied location, mobile substrates, tectonism, and antecedent deposits created rugose topography on the continental slope. Local gradients ranged between -2º (uphill) and 8º , but channel thalwegs had a narrower range between 0.5º and 2º. Sediment gravity flows show a range of erosional and depositional responses across gradient changes. Abrupt decreases in local gradient led to decreased erosive power, decreased flow confinement, rapid deposition, channel widening, and distributary patterns. At similar sites, debris flows exhibited frictional freezing. Conversely, abrupt increases in local gradient led to incision, increased confinement, narrow channels, and knickpoints. Sinuosity co-varied with gradient, but the specific response differed in each basin. The precise gradients for these responses varied with setting, suggesting that both flow characteristics and local gradient together combined to determined the depositional response.
Overall, pronounced decreases in gradient lead to deposition while increases in gradient lead to erosion. Through time, this behavior smoothes the channel thalweg, trending towards equilibrium. This analysis suggests that few slope channel systems achieve final equilibrium state.
AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana