AUTOGENIC ORGANIZATION OF SYN-TECTONIC SEDIMENTARY PATTERNS AROUND DEEP-WATER DETACHMENT FOLDS: A SIMPLE DYNAMIC MODEL

We present a dynamical model that links through multiple length and time scales the formation of detachment folds, degradation of topography, and deposition of sheet-like sedimentary bodies in deep-water foldbelt environments based on a nonlinear reaction-diffusion equation. We focus on deep-water environments since feedbacks between sediment dispersal and fold growth are greatly enhanced in this environment. Notably, the system behaves as a damped spring-mass system or perhaps more exactly as a mass-spring system with friction. The system behaves “overdamped”, under certain conditions, i.e., it decays to an equilibrium state characterized by a steady state stratigraphy, whereas under other conditions it behaves “underdamped”, i.e., it tends to produce an oscillating (autogenic) stratigraphy.

We represent the stratigraphic response predicted by our model in a two-dimensional parametric space whose axes are given by the Peclet number (Pe), the ratio of the mass transported by tectonic uplift and the mass transferred by diffusive hillslope processes, and the sediment delivery number (Sd), the ratio of sediments transported by density currents to those produced by intrabasinal processes. We identify three well-defined regions of sedimentary behavior in that parametric space. A central domain (Pe>2, Sd>2) of cyclic stratigraphy produced by self-sustained oscillations in the sedimentary system, and two regions near the graph axes of stable sedimentation in which a continuous stratigraphy is produced. In the central domain, all the system mass fluxes are equally important. This creates the conditions for a series of complex interaction between hillslope sediment transport, fold growth, and sedimentation. The other two regions correspond to end-members in which either the or are small. For small values, topographic degradation and sediment dispersal by hillslope transport dominates over tectonic uplift. Thus, any tectonic perturbation appearing in the system dissipates readily. For small values, sediment transport is dominated by creep, and the system rapidly evolves toward a steady state.