Characterization of seafloor sediment and morphology offshore from the Northern Channel Islands, California

Nick Poser

Nick Poser
BS Candidate
Advisor: Dr. Shannon Klotsko and Dr. Jillian Maloney

Friday May 10th, 2019
CSL 422 1:10 pm

Abstract
New high-resolution multibeam bathymetry and acoustic backscatter data were collected and processed along with previously collected chirp data from the shelf offshore the Northern Channel Islands, California. These display patterns of sediment distribution, tectonic deformation, seafloor geomorphology, and lithology. The combination of these datasets will help to identify changes in seafloor lithology, for example between rock, gravelly-muddy sand, muddy sand, and mud. Results can be used for numerous studies, including applications to mapping of submerged archaeological resources and benthic habitat distribution. The four Northern Channel Islands were once a unified landmass known as “Santarosae” during the last glacial maximum when global sea level was approximately 120 meters lower than today. The presence of numerous paleocoastal archeological sites on the modern islands suggests that similar sites may exist on the submerged shelf. Mapping seafloor and sub-seafloor geology can identify paleolandforms that may have provided resources and been occupied by early people living on Santarosae. Between Santa Cruz and Santa Rosa Islands, folded beds of Monterey Shale are truncated by a strong acoustic reflector interpreted to be the transgressive surface created by sea level rise since the last glacial maximum. To the North of Santa Rosa Island, there is a continuous trend of volcanic rocks observed both at the seafloor and buried below marine sediment. Sediment thickness above the transgressive surface and volcanic bedrock varies widely across the survey area due to differences in tectonic and hydrographic influences. Understanding these structural and hydrographic controls of the seafloor morphology will improve predictive modeling of submerged archaeological sites for better resource management.