This paper provides information on the geological and geophysical studies of the structure of the Charlie Gibbs megatransform system in the North Atlantic on cruise 50 of R/V Akademik Nikolaj Strakhov in September–October 2020. The preliminary results of the expedition are discussed.

The geological and geophysical data obtained during the 50th cruise of R/V Akademik Nikolaj Strakhov on the Charlie Gibbs megatransform system structure in the North Atlantic are presented. The structure of the Charlie Gibbs Fracture Zone was examined in detail, considering previously published data. It has been shown that the northern and southern segments of the Mid-Atlantic Ridge, separated by the Charlie Gibbs transform fault, are entirely different in morphology, and hence in terms of formation. The dredged rocks are represented by an entire spectrum from the mantle to upper crustal varieties and allow us to determine the origin of the main structures of the Charlie Gibbs megatransform system considering detailed data on the morphology.

Sedimentary waves are represented by a series of wavelike accumulative features with various degrees of morphological expression. These morphological forms are superimposed on the underlying surface with a clear stratigraphic unconformity. The hydrophysical processes are the main relief-forming factors of such features. During expeditions 38 (2018) and 41 (2019) of the R/V Akademik Nikolay Strakhov, the seafloor was mapped between the Kanin Peninsula and inlet of Cheshskaya Bay and new data were acquired on the morphology sedimentary waves. New data obtained in summer (July–August) 2019 show rapid changes in the natural hydrodynamic environment influencing the alternation of the sedimentary waves. The occurrence of hazardous natural processes, geological and geomorphological risks, and the level of threats were identified, especially with respect to the prolonged navigation period along the Northern Sea Route.

The paper analyzes original data obtained on the Atlantis‒Meteor seamount system during Cruise 33 of the R/V Akademik Nikolai Strakhov in the eastern North Atlantic. This system is a volcanic rise formed on the Canary abyssal plate and represents one of the key objects for understanding the geological history of opening of the central segment of the Atlantic Ocean. Basalts, tephrites, and organogenic terrigenous lagoonal marine sediments dredged from the Atlantis, Plato, and Cruiser seamounts are considered. Petrography and compositions of the Atlantis and Cruiser basalts reflect significant differences in settings of their eruptions. Well-crystallized vesicle-free olivine basalts from the Atlantis Seamount were ejected under deep-water conditions. Glassy vesicular basalts of the Cruiser Seamount are typical of shallow subaerial eruptions. Evidence for the accumulation of tuff breccias and tuff gravelstones of the Plato Seamount in subaerial settings are obtained. Tendencies were revealed in the lithogenetic transformations of organogenic‒terrigenous sediments of the Cruiser Seamount, which were subjected to the high-temperature impact of subaerial lava flows. During the volcanosedimentary lithogenesis, the plant lignite-like matter lost its primary structure and was transformed into anisotropic coke with the wide development of fusinite and pyrofusinite. The studied volcanic occurrences are thought to be related to the final (Late Miocene‒Pliocene) volcanic stage in the seamount system, which predated the destruction of the system, its prograde subsidence, and transformation of islands into guyots.