Pockmarks morphology at the Barents sea shelf and its determining factors

Based on the results of complex geological and geophysical works carried out during the 38th, 52nd and 56th cruises of the R/V “Akademik Nikolaj Strakhov” and the 51st cruise of the R/V “Akademik Boris Petrov”, the fluidogenic relief was studied in detail at five key polygons in the southern and northeastern parts of the Barents Sea shelf. Digital elevation models of sea bottom obtained as a result of multibeam bathymetric survey allowed identifying of 2218 pockmarks. Their diameter varies from the first dozens of meters to 250 m, and the depth from 0,2 to 7,8 m. The morphometric analysis of these landforms provided for studying the relationship between the area, depth and shape of the pockmarks cross-sectional profile and physical geographic conditions (tectonic structure, lithology of Quaternary sediments, background topography, hydrological conditions). The distribution of pockmarks and other manifestations of degassing is traceable associated with the fault network. It acts as a pathway for fluid uplift from the gas-saturated sediments of predominantly Mesozoic age to the surface, which proves the deep origin of fluids. The tectonic structure of the area is also reflected in the mutual location of pockmarks within the polygons: the areas of increased density of landforms are near fault zones and in depressions, which are probably of tectonic origin. It was found that the morphology of pockmarks is primarily determined by the lithology of the Quaternary sediments. Large landforms with a more gentle profile are more common in the areas with sandy loams and sands. Small landforms with a V-shaped cross-sectional profile are within the areas with denser clay sediments. It was suggested that the deepest pockmarks occur in the areas covered by glaciers in the recent past. It may be related to active degassing of sediments after removal of the glacial load. Modern exogenous subaquatic processes have a significant influence on the change of pockmark morphology. The slope processes make the cross-sectional profile of pockmarks more complex, i. e. asymmetric and micro-stepping, while the influence of bottom currents leads to landforms elongation.