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The Progradation of a Delta on a Mobile Substrate: Experiment


Understanding the two way interaction between sedimentation and substrate deformation is imperative for unraveling stratigraphic signatures. Previous experimental studies have explored the progression of deltas with varying and steady sea level, tectonic movement, and/or sediment supply rates. In the experimental setting, these external forcings are independently controlled and do not change in response to delta progradation. What still remains to be explored and what we emphasize here are the differences between subsurface architecture developed on a rigid basement and a mobile basement, which deforms as a delta advances. Understanding these differences is key for improving stratigraphic interpretation. We conducted a series of experiments at the University of Texas at Austin to discover the effect of a mobile substrate on an evolving delta. All of the runs had constant sediment supply, water supply, and base level, but the mobile substrate thickness varied from 0 cm to 3 cm. The substrate used was a low viscosity polymer that has the ability to deform in a matter of just a couple of hours. The experiments including the polymer produced dynamic changes in the surface topography of the mobile substrate. In fact, the polymer lying underneath the delta deformed into an undulatory surface that resembled a sinusoidal curve. These undulations also increased in amplitude, but decreased in frequency with increased distance from the upstream sediment source. Furthermore, the overall progradational rate of the delta decreased with the addition of polymer due to further subsidence into the mobile basement.