INTERPLAY BETWEEN DEFORMATION AND SUPERFICIAL MASS FLUXES IN DEEP-WATER COMPRESSIONAL SYSTEMS

In compressional systems, deformation, mass wasting and sedimentation are fully coupled phenomena. These mass fluxes interact with each other controling the evolution of the topography and deposition of growth strata. It is important to model these interactions because they allow us to constrain critical parameters of the kinematics of deformation, sedimentation dynamics, and degradation of the topography. Understanding these interactions may therefore be of economic relevance to the petroleum industry. This work presents a numerical model that simulates the kinematic evolution of detachment folds but which incorporates the dynamics of the different superficial mass fluxes associated with the deformation process. The deformation is governed by the continuity equation (the principle of mass conservation) and considers a stationary Eulerian velocity field in which shortening rate is constant. The degradation of the topography, on the other hand, is represented by a nonlinear slope-dependent transport model proposed by Andrews & Bucknam (1987). In this model sediment flux increases rapidly where hillslope angle approaches to a critical value, θ_c , representing the angle at which episodic superficial mass movements, like granular avalanches, are developed. Additionally, the sediment load transported in suspension is modeled as a function of the Stokes’ settling velocity, the horizontal fluid velocity, and the topographic gradient. Numerical experimentation shows that hillslope retraction and nonlinear mass diffusion are controlled by the Péclet number, Pe, a number lumping the tectonic forcing, fold amplitude and mass diffusion coefficient in a single non-dimensional parameter. If Pe is small nonlinear diffusion dominates in which case erosional surfaces are developed bounding autocycles product of the dynamics of erosion/sedimentation. In contrast, if θ_c is high, linear diffusion dominates and smooth structures with rounded crests develop. Otherwise, nonlinear diffusion dominates resulting in folds with straight hillslopes and angular crests. We further compare the numerical results with seismic images of deep-water detachment anticlines in the western Gulf of Mexico. Our simulations are in excellent agreement with the stratigraphic relations observed in the seismic cross-sections.