44-4 Building and Reworking Delta Plains Under Rising Seas: Experimental Insights into Delta Aggradation and Erosion

Abstract:

River-dominated deltas are complex geological landforms that connect and influence both fluvial and marine processes. The movement of sediment and water across the delta surface alters delta plain topography and affects local ecosystems as well as coastal communities. Once buried, sediment deposited by distributary channels can be preserved, creating pathways for subsurface fluids, forming reservoirs and aquifers. Previous studies describe autogenic cycles, that encompass periods of channelized flow followed by sheet flow on the delta topset. This cyclicity is a fundamental component of aggradation and channel migration across the delta topset, which strongly influences subsurface architecture of the delta. This study utilizes a physical laboratory experiment (QCDS24) to investigate how sustained sea-level rise drives spatial and temporal trends in delta plain aggradation and erosion. The QCDS24 experiment simulates a river-dominated delta with a stable and continuous influx of water and sediment, while undergoing constant steady sea level rise. The sediment mixture contained quartz sand, glass beads, ceramic microspheres and bentonite. The experiment ran for a duration of 300 hours with a constant sea-level rise of 0.5 mm/hr and a constant sediment (0.00022 L/s) and water flux (0.22 L/s). Data from the experiment was collected in the form of topographic scans, overhead images and physical sediment samples taken as peels from the final deposit. The dataset obtained from this experiment will allow for the investigation of links between autogenic cycles, distribution of aggradation across the delta surface and the corresponding subsurface stratigraphy. We will present preliminary results of spatial and temporal trends in aggradation and erosion of the surface and how this relates to the mobility of channels. Future work will focus on combining the temporal and spatial surface data to the subsurface architecture.

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