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Abstract: The Slope Readjustment Model: A New Model for the Development of Submarine Fan/Apron Deposits

W. C. Ross, B. A. Halliwell, J. A. May, D. E. Watts, J. P. M. Syvitski

A new model is proposed for the formation of submarine canyons and submarine fans/aprons. Numerical simulations of basin fill are utilized to illustrate simple concepts of slope grading. This modeling suggests that erosional truncation, sediment bypass, and marine onlap of submarine fan/apron complexes are formed in response to changing basin physiography. Two kinds of basin margins are identified:

1. Progradational margins represent the basinward advance of graded depositional profiles formed when diffusive and sediment gravity flow processes are in equilibrium with sediment supply, basin subsidence, and basin physiography.

2. Erosional margins form when upper slope gradients exceed an equilibrium grade and are characterized by erosion, slumping, and sediment bypass to lower slope environments via sediment gravity flow processes.

Erosional margins are transformed into progradational margins when the bathymetric escarpment (i.e., an oversteepened margin) is buried by onlapping and aggrading fan/apron deposits. Progradational margins can develop bathymetric escarpments and become erosional in response to a rapid rise in

relative sea level, structural deformation of basin profiles (e.g., faulting), and/or a transition from carbonate to siliciclastic deposition. In contrast to eustatically-driven lowstand systems tract models, slope unconformities and onlapping submarine fan/apron systems do not require rapid sea level falls. Rather, the slope readjustment model provides a mechanism for sediment bypass and submarine fan development based on slope grading in response to changes in basin physiography.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994