Abstract

When interpreting environmental signals in the deep marine sedimentary archive, separating the record of local flow and sediment dynamics from that of the terrestrial transport system that feeds it can be challenging. We used a physical experiment to study the dynamics of flow and sedimentation on a prograding, hyperpycnal flow-dominated delta, shelf and submarine slope subject to slow rates of base-level rise (pseudo-subsidence). Our experiments are most relevant to shelf margins where sediment-rich deltaic systems can prograde towards the shelf-edge under relatively mild rates of relative sea-level rise, e.g. recent millennia (~7 ky). Our results offer interesting insight into linked dynamics of terrestrial and submarine transport systems; they apply to time-scales that range from days to millennia, and may be relevant to problems as diverse as delivery of dissolved and particulate anthropogenic pollutants to deep ocean ecosystems and terrestrial paleoenvironmental reconstructions from marine sedimentary records.We asked 3 questions: (1) Are delta channel dynamics reflected in flow and sedimentation on the continental slope? (2) how effectively do shelf and slope systems transfer information from upstream? (3) how does delta growth and progradation to the shelf-edge impact sedimentation on the continental slope? We found that: (1) Changes in flow partitioning through delta-top channels and associated hyperpycnal plume dynamics are recorded in flow and sedimentation on the slope. Channelized delta-top flow resulted in higher localized water discharge and sediment concentrations, and thick, fast-moving, and laterally continuous, turbidity currents on the slope; sheet flow on the delta top, on the other hand, produced thin, slow-moving and laterally discontinuous turbidity currents on the slope. (2) Patterns in flow and sedimentation correlate over longer distances on the advection-settling-dominated subaqueous continental slope than on the transport-limited shelf and delta-top. (3) Delta progradation played an important role in defining the scales of depositional topography and sedimentation dynamics on the slope. Before the delta arrived at the shelf edge, slow-growing, small wave-length depositional topography on the slope remained temporally persistent, and was associated with small cross-stream wavelengths associated with depositional topography and low variance in sedimentation patterns; once the delta reached the shelf-edge, the growth, progradation and lateral stacking of mouth bars on the proximal parts of the continental slope caused an abrupt switch to dynamic depositional topography with large cross-stream wave-lengths and high variance in sedimentation rates.

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