Equilibrium Profile and Baselevel in Submarine Channels: Examples from Late Pleistocene Systems and Implications for the Architecture of Deepwater Reservoirs
Published:December 01, 2000
Carlos Pirmez, R. T. Beaubouef, S. J. Friedmann, D. C. Mohrig, 2000. "Equilibrium Profile and Baselevel in Submarine Channels: Examples from Late Pleistocene Systems and Implications for the Architecture of Deepwater Reservoirs", Deep-Water Reservoirs of the World, Paul Weimer
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Modern submarine channels in a variety of tectonic settings display relatively smooth longitudinal thalweg depth profiles despite the topographic irregularity of the adjacent seafloor. The erosional and depositional action of turbidity currents over periods of thousands of years leads to the development of a depth profile tending to an equilibrium condition, i.e., with a local slope such that the prevailing sediment discharge is carried through the channel with minimum aggradation or degradation. Where sedimentary processes are the dominant shaping mechanism, the equilibrium channel tends to assume a concave-up thalweg profile, as illustrated by the modern Amazon and Rhône Fan channels. Where the rates of tectonic deformation are comparable to the sediment flux, the thalweg profile smoothes irregularities but reflects, in part, the motion of active structures, as illustrated by intra-slope channels in the Gulf of Mexico and offshore Nigeria.
Disruption of the equilibrium profile occurs when the rates of tectonic deformation (e.g., faults and/or folds) exceed the sediment flux or when there is a systematic change in the sediment flux compared with the prevailing flow conditions. Channel avulsion and down-to-basin normal faults are a common expression of equilibrium disruption, with introduction of a steeper segment along the thalweg profile. Three-dimensional seismic and sidescan sonar images illustrate in detail the various processes of equilibrium disruption and stages associated with equilibrium re-establishment. These include thalweg down cutting and meander cut-offs updip of knickpoints, development of distributary channels and sheets as aggradation progresses downdip, and channel damming and redirection associated with up-to-basin normal faults and folds. The mechanics of equilibrium profiles in submarine channels is key to understanding the type and spatial distribution of reservoir elements in deepwater systems.