Abstract: 

High-resolution Autonomous Underwater Vehicle (AUV) multibeam bathymetry and chirp subsurface profiles from a portion of the Lucia Chica channel system, offshore central California, provide imaging of small-scale morphologies associated with deep-water channel migration. From ∼ 950 m to ∼ 1250 m water depth, the Lucia Chica channel system contains a complicated pattern of channels and scours. The quality and resolution of the subsurface chirp profiles reveals sediment packages on the same scale as geometries from outcrop strata. Detailed mapping and measurements along channels, here numbered from oldest (1) to youngest (4), indicate that the sinuous Channel 2 shifted position in discrete lateral steps, typically associated with erosion and new channel incision. Where channel fill was not removed by incision, a bench, morphologically defined as a relatively flat, higher area adjacent to the axial channel, resulted from each lateral shift. Inner-bend levees were deposited on each bench and draped over the previous levees as flows travelled through the new channel position. Using the dense grid of high-resolution AUV-collected images from Channel 2 as an example, we propose a conceptual model of punctuated lateral migration, associated with inner-bend benches formed during axial-channel and outer-bend erosion, instead of point bars, associated with gradual lateral accretion. Greater erosion during punctuated migration as compared to lateral accretion has important implications for reservoir distribution and connectivity.

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