S.J. Friedmann1,
R.T. Beaubouef1,
C. Pirmez2,
D.C. Jennette1
(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