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Coupling Between Sedimentation and Deformation: How Emergence of Mini-Basins Connects to Turbidity-Current Sedimentation

Abstract

Exactly how sediment delivery systems co-evolve with a mobile substrate remains incompletely understood because the feedbacks have not been completely explored. The nonlinear elements of the coupled systems constitute a complex system that leads to the emergence of mini-basins. In a complex system, the emergent phenomena cannot be simply derived or predicted without parallel descriptions of the system at different levels of organization (Kwapien and Drozdz, 2012). Thus, we use physical modeling to investigate the coupling and to generate a data set that can be used to test numerical models. Seventeen strongly depositional turbidity currents composed of one percent silica mud by volume were released at an updip point source and flowed across an initially horizontal surface mobile substrate that was 50 mm thick. We measured the evolution of the upper deposit surface and the basal sediment-substrate interface using a distancing laser and an acoustic transceiver, respectively. Successive measurements of both define deformation of the substrate and resulting subsidence of the turbidites due to spatially variable loading. Results include: 1) maximum subsidence where the deposit was thickest; and 2) normal faulting that segmented the deposit. The localized strain expressed as normal faulting was one order of magnitude smaller than the maximum subsidence produced by lateral flow of substrate away from the maximum sediment load. The modification of surface topography by the spatially varying subsidence pattern and the horsts and grabens associated with active normal faulting was sufficient to alter subsequent sediment routing and depositional pattern associated with the later turbidity currents. As a result, thicker deposits were laid down further away from the channel-lobe transition point. We hypothesize that segmentation of the initially unconfined turbidites by faulting must be combined with the larger-scale subsidence pattern to accurately characterize the emergence of minibasins.