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#           Pockmarks offshore Big Sur, California provide evidence for recurrent, regional, and unconfined sediment gravity flows      

      May 21, 2024    

Recent surface ship multibeam surveys of the Sur Pockmark Field, offshore Central California, reveal >5,000 pockmarks in an area that is slated to host a wind farm, between 500- and 1,500-m water depth. Extensive fieldwork was conducted to characterize the seafloor environment and its recent geologic history, including visual observations with remotely operated vehicles, sediment core sampling, and high-resolution, near-bottom Chirp and multibeam surveys collected with autonomous underwater vehicles to capture the morphology and stratigraphy of the pockmarks. No evidence of high methane concentrations in sediments, chemosynthetic biological communities, or methane-derived diagenetic byproducts was found. Chirp data and sediment cores showed alternating layers of slowly accumulating hemipelagic drapes interrupted by more reflective turbidite horizons that extend throughout the pockmark field and beyond. Chirp data showed multiple episodes of lateral migration over time in some of the pockmarks in association with erosion and infilling events. Laterally continuous turbidite horizons that overlay erosional surfaces indicated that pockmark migration occurred synchronously in multiple pockmarks separated by tens of kilometers. These shifts are presumed to be the result of asymmetrical erosion of the pockmark flanks caused by passing sediment gravity flows. While some pockmarks occur in chains, most are not clustered or randomly spaced but are regularly dispersed within the pockmark field. We hypothesize that intermittent, unconfined sediment gravity flows occurring over at least the last 280,000 years are the source of the regionally continuous turbidite deposits and the mechanism that maintained the regularly dispersed pockmarks.

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####             Maureen L Walton, PhD (Former Employee)          

##### Research Geologist

Pacific Coastal and Marine Science Center

####             Nora Nieminski (Former Employee)          

##### Research Geologist

Pacific Coastal and Marine Science Center

#### Mary McGann

##### Research Geologist

Pacific Coastal and Marine Science Center

mmcgann@usgs.gov

650-329-4979

#### Thomas Lorenson

##### Physical Scientist

Pacific Coastal and Marine Science Center

tlorenson@usgs.gov

831-460-7410

#### Guy R Cochrane, PhD

##### Research Geophysicist

Pacific Coastal and Marine Science Center

gcochrane@usgs.gov

831-460-7554

#### Jason A. Addison, Ph.D.

##### Research Geologist

Geology, Minerals, Energy, and Geophysics Science Center

jaddison@usgs.gov

650-329-5271

## Related Content

####             Maureen L Walton, PhD (Former Employee)          

##### Research Geologist

Pacific Coastal and Marine Science Center

####             Nora Nieminski (Former Employee)          

##### Research Geologist

Pacific Coastal and Marine Science Center

#### Mary McGann

##### Research Geologist

Pacific Coastal and Marine Science Center

mmcgann@usgs.gov

650-329-4979

#### Thomas Lorenson

##### Physical Scientist

Pacific Coastal and Marine Science Center

tlorenson@usgs.gov

831-460-7410

#### Guy R Cochrane, PhD

##### Research Geophysicist

Pacific Coastal and Marine Science Center

gcochrane@usgs.gov

831-460-7554

#### Jason A. Addison, Ph.D.

##### Research Geologist

Geology, Minerals, Energy, and Geophysics Science Center

jaddison@usgs.gov

650-329-5271

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####               Pacific Coastal and Marine Science Center          

2885 Mission StreetSanta Cruz, CA95060United States

831-460-7401

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