Interactions Between Delta Growth and Substrate Deformation Observed in Physical Experiments

Physical (flume) experiments were undertaken to observe the feedbacks between sedimentation on model deltas composed of sand and loading-induced migration of deformable substrates consisting of mixtures of kaolinite and water. The purpose was to provide insights into natural systems in which the weight of deltaic deposition mobilizes undercompacted marine muds and, as a consequence, the deltas become captured within rapidly subsiding, growth-faulted compartments. The experimental deltas were observed to prograde over the deformable substrate which simultaneously migrated from below the clinoform rollover to the region basinward of the delta foreset through internal shearing. Consequently, the deltas experienced subsidence, faulting, and stratal growth at their shorelines and uplift of a decollement-based, internally sheared critical-taper wedge beyond their toes. Rates of substrate migration slowed as the critical wedges grew larger until the deltas would overtake the substrate wedges to create new subsidence and uplift loci basinward of the previous structures. Key variables affecting growth-fault formation, persistence, and abandonment are the substrate rheology (controlled by kaolinite-to-water ratios) and overburden-to-substrate thickness ratios. The results of this study have implications for the interpretation of upper crustal and surficial conditions from growth-faulted stratal successions at the scale of both deltas and continental margins, as well as for the improvement of predictive land-building models used in coastal restorations. The subsidence generated by substrate migration influences not only the mass requirements for deltaic land building, but also may impact the behavior of the lowland river on the delta plain.

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California