Quantifying the
Spatio-Temporal Evolution of a Channel Complex from
Offshore
Strachan, Lorna J.1,
Chris Leppard2, Rob L. Gawthorpe3 (1) The University of
Manchester, Manchester, United Kingdom (2) Norsk Hydro,
Bergen, Norway (3) University of Manchester, Manchester, United Kingdom
The idea that turbidite
slope channels have a propensity towards a graded equilibrium profile has been
successfully applied to many submarine channels. The equilibrium profile hypothesis
- which predicts that longitudinal thalweg depth
profiles will adjust to gravity-base-level through erosion, by-pass and
deposition - seems to fit well with observed gross channel characteristics in
tectonically quiescent and active settings.
This presentation uses subsurface 3D
seismic data from offshore
Detailed analysis of downslope
channel complex trends reveals: 1. an irregularly shaped longitudinal depth
profile, characterized by an erosive thalweg trace;
2. a mismatch between channel complex incision and gradient whereby incision
reaches a local minimum on the steepest slope segments; 3. a decrease in
cross-sectional area downslope; 4. an increase in
width downslope; and 5. a decrease in thickness downslope, with local perturbations close to intra-slope
lows.
Iso-proportional slice
attribute maps taken through the channel complex reveal rapidly changing planform shapes, characterized by multiple, sinuous thalwegs and cut-offs interpreted as resulting from
avulsion, re-incision and abandonment.
These characteristics suggest that the
channel complex was in a state of disequilibrium throughout its
existence. A spatio-temporal evolutionary model for
the channel complex has been developed reflecting this state. We conclude that
variations in turbidity current flow properties and gravity-base-level varied
more rapidly with time than the depositional-erosional
equilibrium response resulting in a near constant state of disequilibrium.
AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California