Imaging the Channel-to-Lobe-Transition Zone With High-Resolution AUV Bathymetry: Navy Fan Offshore Baja California

Abstract

In deep-sea fans the zone across which channels pass to lobes has been difficult to study. The difficulty arises because the zone shows subtle transitional morphologies and geomorphological changes that are hard to resolve with the limited resolution of surface-ship acquired bathymetry and conventional seismic data. To investigate this zone we used an Autonomous Underwater Vehicle (AUV) to acquire high-resolution (1×1×0.25 m) multi-bean bathymetry in the Navy Fan offshore Baja California. The Navy Fan has provided observations and interpretations that have been influential through decades, and it was in this fan where the first observation of a lobe was made. The new AUV bathymetry reveals, in unprecedented detail, an abundance of unrecognized seafloor textures including transitional morphologies, scours, gradient changes and waveforms. Most notably the survey area does not show the originally interpreted lobe. Instead, it is observed over several kilometers a channel (~230 m wide and ~10 m deep) that passes basinward to transitional morphologies that are wider (650-1000 m), shallower (3-5 m), and that induced turbidity current transformation and deposition from hybrid flows. These new data challenge existing models for the channel-to-lobe-transition zone (CLTZ); high gradients established by structure and sedimentation show prominent scouring, likely cut by accelerating and bypassing turbidity currents. Lower gradients sectors downdip show smaller scours, possibly originated from hydraulic jumps. Scours and waveforms are along similar trends in orientation and at times merge laterally suggesting a possible genetic linkage in which scours originated from an original waveform. We speculate that scours and waveforms may be cyclic steps, net erosional and net depositional respectively. AUV multibeam technology has enabled a step change in the imaging, characterization and interpretation of the CLTZ contributing to address a significant challenge in deep-sea fans research.

AAPG Datapages/Search and Discovery Article #90291 ©2017 AAPG Annual Convention and Exhibition, Houston, Texas, April 2-5, 2017