АМПЛИТУДЫ ДИЗЪЮНКТИВНЫХ НАРУШЕНИЙ ФЛАНГОВ ХРЕБТА КНИПОВИЧА (СЕВЕРНАЯ АТЛАНТИКА) КАК ИНДИКАТОР СОВРЕМЕННОЙ ГЕОДИНАМИКИ РЕГИОНА

The Pechora Sea is optimally located for studying the coalescence of a glacial and periglacial continental shelf zone in the high Arctic. Here, we present data acquired during cruises of the RV Akademik Nikolaj Strakhov in 2018–2021, revealing the distribution of submarine glacial landforms in the central part of the Pechora shelf area. Based on moraines and the distribution of glacial lineations, the extent of the ice sheet during the Last Glacial Maximum (LGM) is proposed. The crests of the moraine ridges and the slopes of their sides express a variation in morphology, and the ridges combine into irregular complexes. The moraines are primarily composed of coarse cobble-sized material with an addition of coarse sand and other sedimentary fractions. The mapped glacial landforms clearly indicate that an ice sheet extended over the area, while the Pechora basin, at the same time, was comprised of lowland characterized by a cryogenic subaerial landscape. Based on the result from this study, the extent and ice-flow pattern of the Barents-Kara Ice Sheet during the LGM were determined.

The study is based on the results of multibeam echo-sounding and high-frequency seismic profiling during the 2018-2022 cruises of the R/V “Akademik Nikolai Strakhov” and “Akademik Boris Petrov”. Regular changes of morphometric parameters and the internal structure of pingo-like formations of the shelves of the Pechora and Kara seas were revealed. A morphometric analysis of pingo-like formations was carried out, which made it possible to draw conclusions about their relative age, as well as the role of near-bottom currents and slope processes in their modern dynamics. It was found that the density and morphological variety of pingo-like formations depend on the geological and tectonic features of the bottom area, the presence and nature of permafrost, the intensity of degassing, and the time of shelf flooding during the Holocene transgression. Pingo-like formations on the shelf, where the depth exceeds 70-80 m, emerged at the early stages of the Holocene transgression, and by now the permafrost there has largely thawed out. At the same time, pingo-like formations are still prominent in the relief and actively transformed by bottom currents, slope and, possibly, pseudovolcanic processes associated with ongoing degassing. Pingo-like formations are rare within shallow (up to 20-30 m) shelf areas close to the shore, and, apparently, continue their evolution at present. At the same time, the large thickness and continuity of permafrost prevent active fluid flow, acting as a seal. Pingo-like formations in the shallow-water zones are mainly cone-shaped mounds without intensive degassing. The density of pingo-like formations is maximum at the intermediate depths (from 20-30 to 70-80 m), in the presence of insular or discontinuous permafrost, under high fluid flow intensity within the fault zones and oil- and gas-bearing structures. Near-surface sediments in such areas are characterized by a combination of localized processes of heaving and active degassing. It predetermines a wide variety of the morphological types of pingo-like formations.Keywords: Arctic, bottom topography, degassing, pingo-like features, acoustic anomalies, multibeam echo sounding, seismoacoustic profiling

The results of detailed geological and geomorphological studies in the waters of the Pechora Sea using a complex of hydroacoustic methods during the 52nd cruise of R/V Akademik Nikolaj Strakhov revealed numerous gas funnels (pockmarks) at the bottom of the Southern Novaya Zemlya Trench. These forms are widespread over a considerable part of the bottom of the Barents Sea, but for the Pechora shelf, there is little information about their distribution. The analysis of the seismoacoustic sections at the sites of development of gas funnels showed the presence of vertical chimneys in unconsolidated sediments of the Southern Novaya Zemlya Trench, which allow gas to rise to the bottom surface and to escape into the water column with the formation of negative landforms, which is accompanied by the detachment of bottom sediments.

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.

The results of detailed geological and geomorphological studies in the waters of the Pechora Sea using a complex of hydroacoustic methods in the 52 cruise of the R/V “Academic Nikolaj Strakhov” revealed numerous gas funnels (pockmarks) at the bottom of the Yuzhno-Novozemelsky trench. These forms are widespread on most of the bottom of the Barents Sea, while on the Pechora shelf there is very little information about their distribution. Analysis of seismoacoustic sections at the sites of development of gas funnels showed the presence of vertical chimneys in unconsolidated sediments of the Yuzhno-Novozemelsky trench, through which gas rises to the bottom surface and its release into the water column with the formation of negative landforms, which is accompanied by churning bottom sediments.