Long-period cyclic sedimentation with constant tectonic forcing in an experimental relay ramp

It is widely believed that cyclic sedimentation in active tectonic basins is caused by external forcing such as sea-level cycles, episodic tectonic events, or variation in sediment supply due to climate change. Here we present a case of cyclic sedimentation in an experiment subject to constant fault slip rate and sediment discharge with no base-level fluctuation. The experiment was designed to study sedimentation in a simplified extensional relay ramp system. Reorganization of the fluvial channel network in a cyclic manner caused local variation in sediment supply to the hanging-wall basin, where subsidence was maximized, and resulted in autogenic appearance and disappearance of a lake associated with 90° rotation of paleocurrent direction and delta formation. Comparing an early phase of the experiment using no external forcing (ie., no tectonic movement or base-level change) with the following main phase of the experiment (ie., including subsidence in an extensional relay ramp pattern) shows that the characteristic time scale for channel mobility was five times longer during the phase with subsidence than during the previous phase without subsidence. Active fault slip imposed a new, longer time scale for autogenic dynamics by establishing a linked tectonic-sedimentation system. Scaling the experimental results to field length and time scales suggests that comparable autogenic cycles would produce 10-20-m-thick strata on time scales of 10⁵ yr, comparable to observed cases attributed to allogenic effects.