SLOPE READJUSTMENT - A NEW MODEL FOR THE DEVELOPMENT OF SUBMARINE FANS AND APRONS

In a new model proposed for the formation of submarine canyons and sub marine fan-aprons, numerical simulations of basin fill are utilized to illustrate simple concepts of slope grading. This modeling suggests t hat erosional truncation, sediment bypass, and marine onlap of submari ne fan-apron complexes are formed in response to changing basin physio graphy. Two kinds of basin margins are identified. (1) Progradational margins represent the basinward advance of graded depositional profile s formed when diffusive and sediment gravity-flow processes are in equ ilibrium with sediment supply, basin subsidence, and basin physiograph y. (2) Erosional margins form when upper slope gradients exceed an equ ilibrium grade, and are characterized by erosion, slumping, and sedime nt bypass to lower slope environments via sediment gravity-flow proces ses. Erosional margins are transformed into progradational margins whe n the bathymetric escarpment (t.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 sili ciclastic deposition. Whereas relative falls in sea level play a major rote in bringing the source of sediment input to the shelf edge, the development of slope unconformities and onlapping submarine fan-apron systems is controlled primarily by slope-readjustment processes trigge red by changing basin physiography.