June 8 – Masters Presentation by Kristoffer Norman

The origin and development of seafloor cratering on the Lomonosov Ridge, central Arctic Ocean

Thursday, 8 June 2017
13h00, U26, Geohuset, Stockholm University

Supervisor:
Matt O'Regan, Stockholm University

Examiners:
Richard Gyllencreutz, Stockholm University
Benedict Reinardy, Stockholm University

 

Abstract

Seafloor pockmarks, or crater-like depressions, are characteristic features in regions of focused fluid escape. They form by erosion of near surface sediment as fluids discharge into the overlying water column. They are prolific in hydrocarbon bearing regions and where gas hydrates exist in near surface sediments. During the SWERUS-C3 expedition to the Arctic Ocean, a pockmark field was discovered on the Lomonosov Ridge. Geophysical data, including airgun, swath bathymetry and Chirp sub-bottom profiles, were collected during a survey of this region, and are used to test the central hypothesis that the pockmarks formed from fluids escaping organic rich early Neogene and Paleogene sediments. Constant rate of strain consolidation tests were performed on two samples from a sediment core (SWERUS-C3-L2-33GC) collected from one of the pockmarks. The results suggest that both samples share similar geotechnical properties as the Neogene ACEX (Arctic Coring Expedition) and were used to model in situ porosity and thermal conductivity down to 500 mbsf. However, the seismic data reveals that the chimneys underlying the pockmarks only extend ~105 meters below the seafloor, and do not reach the organic rich early Neogene and Paleogene sediments. This is consistent with thermal modeling revealing that the in situ temperature of the organic rich sediments is too low to have caused any thermal maturation and fluid generation. Therefore, the hypothesis that fluid escape from the deeply buried early Neogene and Paleogene sediments is causing pockmark formation is rejected, and other mechanisms for their formation – including possible methane hydrate dissociation, need to be explored.



 

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