ABSTRACT: Shoreline Position in Clastic Wedges of Marine Foreland Basins: A Modeling Study
Rudy L. Slingerland, Kevin P. Furlong
The transgressive-regressive history of an active margin bordering a marine foreland basin is controlled by the relative rates of sediment supply, basin subsidence, and sea level change. The purpose of this research is to better understand the functional relationships among these factors and shoreline position by exploring solutions to a coupled source-basin numerical model. The model consists of a critically tapered, accretionary wedge, and a single-thread river of known discharge and width carrying sediment eroded off the wedge to a basin of specified initial depth, with the elastically deforming lithosphere responding to the tectonic and sedimentary loads. The accretionary wedge, modeled as a steady state critically tapered wedge, provides the initial supracrustal load that creates the basin, the initial slope of the river, and a sediment load the river must carry. The river builds a delta and alluvial plain into a standing body of water of specified surface elevation. The river/transport system is modeled using the equations of unsteady, gradually varied flow, modified Bagnold bed load transport, and conservation of bed material. The lithosphere deforms according to elastic flexure under a distributed supracrustal load. We model the evolution of topography and basin bathymetry from initial conditions to steady state when the sediment flux overpassing the foreland basin equals the convergence flux into the wedge at its toe. The results are strongly dependent upon characteristic times for the competing processes. For example, an increase in the converge ce rate causes an increase in the height and width of the wedge, increasing both the sediment volume to be carried by the river and magnitude of the load. This load increases basin subsidence, allowing additional accumulation of sediments (and loading) in the basin. Depending upon the response time of the sediment delivery system and the amount by which the river is out of grade, the shoreline may either prograde or retrograde.
AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990