The chemical composition of bottom sediments in the Chukchi and, partly, East Siberian Seas was studied. In the south and west of the Chukchi Sea, a zone has been detected with the accumulation of sediments rich in organic carbon, an increased background content and anomalies of sulfophile metals (Mo, Zn, Hg, Ag, Au), iron-group metals (V, Ni, Co), and some PGE (Ru, Pt). This zone is confined to the neotectonic active system of rift troughs extending from the Bering Strait and eastern Chukchi Peninsula to the continental slope, where it is bounded by the Cenozoic Charlie rift basin of the Canadian hollow. The geochemical features of the carbon-enriched sediments evidence that they formed under oxygen-deficient conditions and, sometimes, in suboxic and anoxic environments near endogenic water and gas sources. The high carbon and metal contents suggest that the very fine-grained sediments in the rift troughs of the Chukchi Sea are a possible analog of some types of ancient highly carbonaceous sediments belonging to black shales.

Seismic data on the southern (Laptev Sea) extremity of the Lomonosov Ridge were used to develop a new structural model for the sedimentary cover. It permitted a correlation between the seismic cross-sections of the ridge crest and two deep-sea basins: the Podvodnikov Basin and the Amundsen Plain. It is the first time that a seismic model has taken into account both regional seismic-reflection profiles obtained from NP drifting ice stations and recent high-resolution CDP data. Our seismic model agrees both with geological data on the Laptev Sea continental margin and the data obtained from deep-sea drilling into the Lomonosov Ridge under the IODP-302 project. The sedimentary cover of the southern Lomonosov Ridge and adjacent parts of the Amundsen Plain and Podvodnikov Basin was dated at the Aptian–Cenozoic. The sedimentary section is divided by two main unconformities, of Campanian–Paleocene and Oligocene–Early Miocene ages. The cover contains a structurally complicated graben system, which is an extension of the New Siberian system of horsts and grabens, recognized in the shelf. Sedimentation began in the grabens in the Aptian–Albian and ended with their complete compensation in the Paleocene.

Dating of marine sediments and faunal remains they contain in stratotype and reference sections by the methods of infrared optically stimulated luminescence (IR-OSL) of K-feldspar, optically stimulated afterglow (OSA) of quartz, electron spin resonance (ESR), and 230Th/U provides new constraints on deposition in the Yenisei mouth during the Kazantsevo interglacial. The luminescence and U–Th ages in the 120–68 ka range and 93–70 ka ESR ages show that the deposition spanned the whole marine isotope stage (MIS) 5. The sediment structures and textures, grain sizes and mineralogy, and faunal records indicate tidal and shelf deposition environments. The sampled assemblages of marine mollusks comprise taxa that typically live in relatively shallow and warm water, as well as abundant subarctic and boreal species, including the Arctica islandica index species. The variations of faunal patterns, more likely, had facies rather than climatic controls, while the sediments were deposited during transgression, in a warm climate, when the area was ice-free.

The molluscan shells from three drill and two piston cores obtained in the southern Russian sector of the Chukchi Sea are dated by the AMS 14C measurement method back to 0.8–3.5 and 9.2–10.5 ka. The...