Boris Baranov

Bottom current-controlled sedimentation and mass wasting in the northwestern Sea of Okhotsk

Abstract Quaternary sedimentation in the northwestern Sea of Okhotsk, where tidal and thermohaline currents are active, was studied using 8443 km of high-resolution air gun profiles from four cruises. It is characterized by: (1) bottom current-controlled processes, which lead to widespread deposition of contourite drifts and sediment waves on the North Okhotsk continental margin and the northernmost Sakhalin slope, as well as to erosion and sediment reworking on the northern Sakhalin shelf; (2) mass wasting triggered probably by shallow earthquakes, by gas hydrate instability during sea-level lowstands leading to slumps and debris flows in the western Derugin Basin; (3) deposition of the fluvial load of the River Amur, which results in sediment drift bodies and prograding lowstand wedges during glacial periods, and to contourite drifts and a ‘fan’ during interglacial times; and (4) ice-rafted detritus and hemipelagic sedimentation interrupted by episodic turbidity current activity, especially in the Derugin Basin and its northern, eastern and southern flanks.

Evidence for Compressionally-Induced High Subsidence Rates in the Kurile Basin (Okhotsk Sea)

A combined volcanological, geochemical, paleo-oceanological, geochronological and geophysical study was undertaken on the Kurile Basin, in order to constrain the origin and evolution of this basin. Very high rates of subsidence were determined for the northeastern floor and margin of the Kurile Basin. Dredged volcanic samples from the Geophysicist Seamount, which were formed under subaerial or shallow water conditions but are presently located at depths in excess of 2300 m, were dated at 0.84±0.06 and 1.07±0.04 Ma with the laser 40Ar/39Ar single crystal method, yielding a minimum average subsidence rate of 1.6 mm/year for the northeast basin floor in the Quaternary. Trace element and Sr–Nd–Pb isotope data from the volcanic rocks show evidence for contamination within lower continental crust and/or the subcontinental lithospheric mantle, indicating that the basement presently at ∼6-km depth is likely to represent thinned continental crust. Average subsidence rates of 0.5–2.0 mm/year were estimated for the northeastern slope of the Kurile Basin during the Pliocene and Quaternary through the determination of the age and paleo-environment (depth) of formation of sediments from a canyon wall. Taken together, the data from the northeastern part of the Kurile Basin indicate that subsidence began in or prior to the Early Pliocene and that subsidence rates have increased in the Quaternary. Similar rates of subsidence have been obtained from published studies on the Sakhalin Shelf and Slope and from volcanoes in the rear of the Kurile Arc. The recent stress field of the Kurile Basin is inferred from the analysis of seismic activity, focal mechanism solutions and from the structure of the sedimentary cover and of the Alaid back-arc volcano. Integration of these results suggests that compression is responsible for the rapid subsidence of the Kurile Basin and that subsidence may be an important step in the transition from basin formation to its destruction. The compression of the Kurile Basin results from squeezing of the Okhotsk Plate between four major plates: the Pacific, North American, Eurasian and Amur. We predict that continued compression could lead to subduction of the Kurile Basin floor beneath Hokkaido and the Kurile Arc in the future and thus to basin closure.

Hydrate‐bearing structures in the Sea of Okhotsk

Gas hydrates are natural gas reservoirs in ice-like crystalline solids, and are stable in pore spaces of submarine sediments in water depths greater than about 300–500 m. They have been recovered in many of the worlds oceans, both at larger sub-bottom depths (up to 450 m) by drilling and near the seafloor in shallow cores by gravity-coring. In the latter case, the gas hydrates are related to the sites of enhanced seepage such as cold seeps and mud volcanoes [Ginsburg and Soloviev, 1998]. Multidisciplinary field investigations during the two cruises have revealed new, large hydrate-bearing seepage structures in the Sea of Okhotsk, a northwestern marginal sea of the Pacific Ocean (Figure l). The Derugin Basin at the central part of the Sea of Okhotsk, the zone of intensive gas seepage and hydrate accumulation, was studied during two cruises of the R/V Akademik M.A. Lavrentyev (LV) of the Russian Academy of Sciences (RAS), in August and October 2003 within the framework of the CHAOS project (hydroCarbon Hydrate Accumulations in the Okhotsk Sea) supported by funding agencies in five nations.

Structural and geological characteristics of a “seismic gap” in the central part of the Kuril Island Arc

The results of the cruise of R/V Akademik M.A. Lavrentiev conducted by the Pacific Institute of Oceanology, Far East Division of the Russian Academy of Sciences and the Shirshov Institute of Oceanology, Russian Academy of Sciences in August to September 2005 are considered. The aim of the works was to specify the tectonic structure, seismogenic potential, and tsunamigenic hazard of the central segment of the Kuril Island Arc. The complex studies involved single-channel seismic profiling, gravimetry, magnetometry, detailed bathymetry, dredge sampling of sea-floor rocks and sediments, and gas geochemistry. Geophysical and geological data are reported. It was demonstrated that the target area is an active tectonic destruction zone, the zone boundaries were outlined, and the main internal structural and compositional heterogeneities were identified.

Seismic stratigraphy, BSR distribution, and venting of methane-rich fluids west off Paramushir and Onekotan Islands, northern Kurils

Abstract Single-channel seismic recording, water chemistry determination, and sediment sampling were carried out off the northern Kuril Islands and the southern tip of Kamchatka. A bottom simulating reflector (BSR) was mapped in detail. The shipboard analyses of bottom water samples yielded methane concentrations up to 1000 nl/1. West off Paramushir Island, venting of methane-rich fluids from the seafloor into the water column is related to unusual trajectories of the BSR which emerges towards the seafloor. The destabilisation of gas hydrates and the origin of the vent site may correspond to anomalous high heatflow caused by recent volcanic intrusions into the sediment. No venting was found in the areas off the southern tip of Kamchatka and off Onekotan Island.

Implications of the seismic source dynamics for the characteristics of a possible tsunami in a model problem of the seismic gap in the Central Kurile region

[1] Various scenarios of earthquakes and the associated tsunami wave generation are numerically simulated. It is shown that, depending on the chosen dynamic source parameters in the central seismic gap zone of the Kurile-Kamchatka arc, the characteristics of tsunami waves in the water area of the Sea of Okhotsk and Kurile-Kamchatka zone can differ dramatically, from insignificant inundation of Sakhalin and Kamchatka coasts to a catastrophic run-up of waves up to 8 m in height. Detailed numerical constraints on the tsunami wave run-up are obtained for a number of points of the Sakhalin coastline, the form of the first waves climbing the coast is determined, and the run-up velocity characteristics are computed.

Submarine Landslides on the Western Slope of the Kuril Basin, Sea of Okhotsk

Landslide processes on the western slope of the Kuril Basin were studied using bathymetry and seismic data obtained under the international KOMEX and SSGH projects. Slope areas containing landslides, landslide blocks and mass-transport deposits were distinguished. Large-scale landslides occupying an area of more than 100 km2 are located in such areas of open continental margins as the slopes of the North Hokkaido Marginal Plateau and Terpeniya Ridge. Landslide blocks up to 2 km in size and mass-transport deposits are located in submarine canyons and fans in Terpeniya Bay. The age of landslides has been estimated as Middle Pleistocene–Holocene. Landslides are most likely triggered by seismic activity and gas saturation of sediments. Subsequent slope failure seems quite probable within the study area, and landslides capable of generating tsunamis may occur.

Structural Evidence of Recent Activity of the Khatanga–Lomonosov Fault Zone in the Laptev Sea

New structural data obtained by a geophysical survey during Cruise 69 of the R/V Akademik Mstislav Keldysh in 2017 indicate that the Khatanga−Lomonosov fault zone is presently active and propagating in Khatanga Bay. The orientation of conjugated extension and compression structures points to the sinistral displacement along this zone. The results confirm the concept that this zone represents a transform fault separating Gakkel Ridge from the rift system of the Laptev Sea shelf.