SENSITIVITY OF CLINOFORM GEOMETRY TO SEDIMENTARY FORCING MECHANISMS; INSIGHTS FROM NUMERICAL MODELS

Physics-based numerical stratigraphic models provide for an ideal platform to examine the geomorphic response of clinoform slopes to changing sedimentary and geological conditions. By adjusting input and/or boundary conditions such as sediment flux, grain size, original bathymetric slope, etc., the response in simulated clinoform shape helps unravel the complex process-response relationships observed in natural clinoform systems.

A series of numerical experiments conducted with the multi-process, stratigraphic model SedFlux demonstrate the evolution of the two-dimensional shape of siliciclastic clinoforms. The experiments were designed to isolate the effect of buoyant river plumes, wave energy, slope failure, debris flows, turbidity currents, subsidence, sea-level fluctuations, and basin depth on clinoform geometry.

Hemipelagic sedimentation from buoyant river plumes exerts the strongest control on overall clinoform profile shape at the scale of our simulated clinoforms (200m – 2000m tall). This basic shape undergoes substantial modification with the adjustment of boundary conditions and additional sedimentary processes. The most dominant of these in determining clinoform slope gradient is the depth of the receiving basin, which controls the height of the clinoform. Clinoforms prograding into 2000m of water have an equilibrium profile that is 5 times steeper than those entering 200m with identical input conditions. If basin conditions are “too deep” (which in our simulations appears to be ~3000m-4000m) the model responds by building up the base of the slope with an excess of mass transport deposition until a stable equilibrium profile can be maintained and the clinoform can prograde. Minor modifications to clinoform shape occur with the predominance of either debris flows or turbidity currents. While debris flows tend to accumulate on and at the base of the clinoform slope and reduce the overall slope gradient, turbidity currents tend to erode and steepen the upper slope and deposit in a more basinward position. Other modifications to clinofrom geometry include topographic smoothing of the clinoform break caused by simulated wave activity which tends to reduce the instances of slope failure and mass transport. Sea-level fluctuations produce surprisingly minor impacts on profile shape.