Мурманская МИЛЯ. 2018 г. №4.

EXPLORATIONS Gakkel Ridge rift valley is notable but the lack of vivid compatibility in the nature of seismic record in the Nansen and Amundsen basins as well. At the same time the general thick­ ness of the Nansen Basin sedimentary cov­ er is twice as large as the thickness of the Amundsen Basin sedimentary cover. The comparative analysis of the adjusted to the reflected and diving P-waves values of interval velocities of coeval sedimentation sequences in the Nansen and Amundsen ba­ sins according to the 2014 expedition data shows certain principles. The velocities are almost identic (1.8-2.3 km/sec in the Amund­ sen Basin, 1.9-2.3 km/sec in the Nansen Ba­ sin) in the Miocene to Quaternary sequence. And the velocities sufficiently vary (2.4-2.7 km/sec in the Amundsen Basin, 2.7-3.3 km/ sec in the Nansen Basin) in the Eocene to Oligocene sequence and (2.8-3.5 km/sec in the Amundsen Basin, 3.5-4.2 km/sec in the Nansen Basin) in the Paleocene and Eocene sequence. The difference in values of the P- waves interval velocities in pre-Miocene se­ quences of two basins cover in the Eurasian Basin can be explained by different sources of terrigenous sediments. It is a standard passive margin for the Nansen Basin, name­ ly the Barents-Kara shelf - the continental margin of the Eurasian tectonic plate and the morphostructures of provinces of the Central Arctic underwater highs for the Amundsen Basin. It also explains a sufficiently less («1.5 times) general thickness of the sedimentary cover in the Amundsen Basin. Another one seismic line essential for the 6 8 Fig. 2. The interpreted section of AR1401 line The North Chukchi Trough - the Podvodnikov Basin section. Рис. 2. Интерпретированный разрез МОВ- ОГТ AR1401 сечения «Северо-Чукотский про-гиб - котловина Подводников». understanding of the Arctic Basin develop­ ment has become line AR1401 shot during the expedition of 2014. It allowed tracing the sedimentary cover structure from the East Siberian Sea shelf to the Podvodnikov Ba­ sin (Fig. 2). As the result of acquired data analysis in which there were involved seismic data obtaine in expeditions of early years (Shelf-2011 and Arctic-2012) within the li­ mits of the province of the Central Arctic un­ derwater highs of the Amerasian Basin there were 7 seismic stratigraphic sequences iden­ tified (SSS). In the Cenozoic part of the sedimentary cover the seismic data correlate with seis­ mic section AWI-91090, calibrated by drilling ACEX IODP 302 on the Lomonosov Ridge (the line crosses the well) [9]. In accordance with dating of the traced unconformities RU and pCU, two seismic sequences are iden­ tified (from top down the section), namely: SSS-1 - N1-Q (low Miocene to Pleistocene) and Paleogenic SSS-2 - E1-E2/E3 (upper Paleocene to mid-Eocene/Oligocene in ba­ sins). Both seismic sequences are continu­ ously traced from the Lomonosov Ridge to the Podvodnikov Basin, Vilkitsky Trough, the Mendeleev High as well as across the transit zone to the Eurasia shelf. The Neogene sequence SSS-1 is rep­ resented by hemipelagic deposits and was formed after the Fram Strait discovery. Ac­ cording to the ACEX data it is composed by aleurolites with sand partings. The adjusted to the reflected and diving P-waves values of interval velocities in SSS-1 vary within the 1.8-2.8 km/sec limits. The Paleogene SSS-2 is specified by extremely low thickness on the Lomonosov Ridge (less than 200 m), on the Mendeleev High and in the west/north-west of the Pod­ vodnikov Basin (300-400 m maximum). Ac­ cording to the drilling data it had formed in the neritic sedimentation environment af­ ter the Laurasia split in to the Eurasian and North American tectonic plates. Most part of the Podvodnikov Basin with low thickness Paleogene sequence may be considered as a submerged side of the Lomonosov Ridge. The adjusted to the reflected and diving P- waves values of interval velocities in SSS-2 vary within the 2.9-3.3 km/sec limits. The interpretation of the pre-Cenozoic sequences of the sedimentary cover of the province in the Central Arctic underwater highs was based on the projection verified by drilling (on the coast and shelf of Alaska [14]) regional seismic and stratigraphic plugs MURMANSK MILE • 4-2018