56-10 The influence of fluvial-tidal dune morphology on preserved cross-strata: A snapshot of the Lower Columbia River (OR/WA)

Abstract:

Subaqueous dunes are prevalent throughout fluvial-tidal transitions and thus dictate channel bed bathymetry and the character of subsurface deposits. Their size, shape, and scale depend on flow characteristics (magnitude, duration, and style) and sediment transport mode (bedload vs suspended load dominated). Thus, varying combinations of sediment size and flow type (unidirectional, oscillatory, bidirectional) lead to changes in the mode of sediment transport, which is reflected in dune morphology and preserved cross-strata. Most riverine and fluvial-tidal transition studies have only investigated dune morphology and have ignored linking how their morphology may be reflected in their preserved cross-strata and if these deposits provide a unique signature that can be used to identify changes in flow and sediment dynamics. Therefore, this study aims to identify how changes in the morphology of dunes affect preserved cross-strata within a fluvial-tidal transition. To accomplish this, we utilize high-resolution multi-beam bathymetric maps in conjunction with subbottom (parametric echosounder) seismic data to compare the morphology of fluvial-tidal dunes with the geometries of their recent subsurface deposits.  

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