ABSTRACT

New high-resolution datasets across La Jolla submarine fan, offshore California, illuminate low-relief, down-dip widening conduits emanating from a deep-sea channel that deposited a combination of laterally extensive sand strata seemingly crisscrossed by distributary patterns. Extensive coverage of this sector of the seafloor shows submarine-fan architecture and morphologies essentially different than distributary channelized patterns characteristic of subaerial systems and previous conceptual models of submarine fans. The main La Jolla channel, connected to La Jolla Canyon, loses confinement by widening, decreasing in relief, and developing scoured margins across kilometers-long down-slope and lateral distances. Two scales of distributary patterns are associated with sand-rich deposits down-system from, and outside of, fully formed channels. A larger-scale distributary pattern is identified in backscatter and bathymetry from trains of preferential erosion associated with laterally continuous repetitive steps that extend for kilometers outside channel confinement and may represent net erosional upper-flow-regime transitional bedforms. Smaller-scale distributary backscatter patterns in unconfined sand-rich deposits originate from the wide, low-relief channel. We suggest that the newly imaged La Jolla seascape displays sedimentary features that may be common on deep-sea fans but missed in previous lower resolution studies of submarine fans. Thus, La Jolla provides the basis for integrating previously enigmatic and (or) incomplete images of submarine fans. High-resolution seafloor, subsurface, and sample datasets highlight the importance of channel widening, headward erosion, and unconfined flows in La Jolla submarine-fan development, and may be relevant to other sandy submarine fan systems.

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