Fe-Mn crusts from underwater rises of the Kashevarov Trough (Sea of Okhotsk)

Dredging on nonvolcanic underwater rises in the Kashevarov Trough area (Sea of Okhotsk) carried out during Cruise 178 of R/V “Sonne” yielded sedimentary (conglomerates), metamorphic (biotite hornfels, tectonic breccia with inclusions of biotite hornfels), and igneous (granodiorite) rocks as well as Fe-Mn crusts up to 15 cm thick. The study of the structural-textural properties and the thorough analysis of the mineral and chemical compositions of these crusts, including the REE and Y distribution, show that the ore sediments are hydrogenic in nature.     

Geological structure of the sedimentary cover and evaluation of the oil and gas potential of the Deryugin Basin (Sea of Okhotsk)

Results of interpretation of the seismic refraction survey in the southern part of the Deryugin Basin are presented. A geological-geophysical model was developed, and a scheme of the sedimentary cover evolution of the basin (Late Cretaceous-Pleistocene) is suggested. The data obtained indicate a high hydrocarbon potential comparable with that of the adjacent oil and gas-bearing shelf of northeastern Sakhalin.     

Neotectonics of the Deryugin Basin area (Sea of Okhotsk)

The data of the bottom “summit” surface were used for compiling the schematic structural-neotectonic map and map of the main neotectonic structural elements. Their comparison with the schematic paleogeographic maps of the lithophysical complexes for four periods (K₂-$ _{1 - 2} $ _{1 - 2} , $ \rlap{--} P_3 $ \rlap{--} P_3 -N₁¹, N₁^1–2, and N₁³-N₂) reveals that the largest part of the considered area was characterized by either a continental or relatively shallow-sea environment, except for the western areas occupied at that time by the relatively deep trough with its axis located substantially westward of the neotectonic Deryugin Basin and the Staritskii Trough. In the Late Pliocene, the deep paleotrough ($ \rlap{--} P_3 $ \rlap{--} P_3 -N₂²) and Deryugin Basin were likely occupied by shelf settings with continuing sedimentation. The paleogeographic environments of the area for the period from the terminal Pliocene to the late Riss (Taz) Glaciation (Q₂⁶; MIS6) are unknown so far. The most complete Quaternary section recovered by Core LV 28-34-2 consists of six units; the odd (1, 3, and 5) and even (2, 4, and 6) among them correspond to the warm and cold marine isotopic stages, respectively. Judging from the benthic foraminiferal assemblages, the water depths during cold periods were shallower as compared with the warm stages, which is explained by the respective ascending and descending bottom movements and, partially, by the eustatic sea level fluctuations. In the Late Pleistocene-Holocene (∼17 ka), the bottom of the Deryugin Basin and the summit part of the Institut Okeanologii Rise subsided with average rates of 8 and 3 cm/year, respectively.     

Geological structure and composition of the Curonian Spit (Baltic Sea)

The paper presents new data on geology of the Curonian Spit based on results of the study of data on the engineering-geological transect compiled during the construction of gas pipe in the Russian sector of the spit. The data show that, along with eolian sand, peat deposits recovered in both its Russian and Lithuanian sectors make up a significant portion of the spit (data on the Lithuanian sector are adopted from the available literature). Based on new data, existing concepts on geology, paleogeography, geoecology, and stability of the Curonian Spit are discussed and refined.     

New data on the structure of the Sea of Okhotsk bottom

The reinterpretation of the time and deep sections along CDP Profile 1632 revealed different previously unknown structural features: (1) a buried bar and a Late Pliocene regional unconformity, the Bol’sheretsk and Lebed subaerial shield volcanoes, and the Koni-P’yagina and Magadan megadikes at its level; (2) morphological evidence for the nappe structure of the Okhotsk Arch (homoclinal thrust slices of the acoustic basement with ramp half-grabens in the frontal part and a pull-apart zone with a solitary diapir in the Kol’skii Trough, which divides the arch into two allochthonous megablocks with opposite vergence of their thrusts), which is related to a divergent sheet decollement, probably, at the M discontinuity.     

The sedimentation model of the Tuapse Trough (Black Sea)

Based on the new 2D and 3D seismic data from the Tuapse Trough (Black Sea), the principle peculiarities of sedimentation have been studied in detail. A sedimentation model of the focused Maikop and Karagan-Chokrak intervals of the geological section has been suggested. A system of fan complexes referred to Maikop age has been found.     

Authigenic Carbonate and Barite Mineralization in Sediments of the Deryugin Basin (Sea of Okhotsk)

Results of the analysis of mineralogy, geochemistry, and isotope parameters (¹³C, ³⁴S, ¹⁸O, and ⁸⁷Sr/⁸⁶Sr) of carbonates and barites from sediments of the Deryugin Basin in the Sea of Okhotsk are presented. The diagenetic nature of carbonates and barites, which are formed as a result of the prolonged activity of cold seeps acting along a fracture zone and supplying methane–and barium-saturated fluids, is determined. Any signs for hydrothermal activity were not observed.     

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.     

Holocene Siliceous Sediments in the Sea of Okhotsk

The mineral and chemical compositions and physical properties of diatomaceous clayey–siliceous sediments in the Sea of Okhotsk are studied. Absolute masses of silica accumulation are determined. Their compositional model based on the silica content is similar to that of Late Jurassic and Olenekian–middle Anisian cherts of the Sikhote Alin region. The thickness of the Holocene siliceous unit and the absolute mass of siliceous deposits depended on bioproductivity in the upper water column and the seafloor topography. Absolute masses of SiO₂ am (0.05–5.7 g cm^–2 ka^–1) and SiO₂ fr (0.5–11.6 g cm^–2 ka^–1) are minimal on seamounts and maximal in depressions near foothills. These values match absolute masses of SiO₂ fr accumulations in Triassic and Late Jurassic basins of the Sikhote Alin region (0.33–3 g cm^–2 ka^–1). Comparison of the composition and absolute masses of silica shows that Triassic and Late Jurassic siliceous sequences of Sikhote Alin could be accumulated in the marginal marine basin near a continent.     

Geological Conditions of the Formation and Dissociation of Gas Hydrates in the Sea of Okhotsk: Tectonic and Genetic Aspects

Lithology and Mineral Resources - The paper is dedicated to gas hydrate fields and active underwater gas seeps found in the Sea of Okhotsk. The study of geological conditions of the generation and...     

论河北丰宁牛圈银（金）矿床的成矿时限问题

南沙海槽的构造和沉积受控于南海的构造运动和加里曼丹西北大陆边缘的演化,具有适于天然气水合物形成的物源基础、温压条件、输导系统和储藏场所。似海底反射层(BSR)出现在水深650~2 800 m、海底下65~350 m深的晚中新世沉积物中,与褶皱、逆冲推覆构造及穹窿构造有关;沉积物中的甲烷含量和孔隙水的SO24-含量表现出异常变化特征,硫酸盐-甲烷界面(SMI)深度仅为8~11 m;表层沉积的自生石膏和黄铁矿的成岩环境与甲烷流体排溢引起的厌氧甲烷氧化(AOM)有关,这些地球物理和地球化学指标均指示南沙海槽发育天然气水合物。研究表明,南沙海槽沉积物的甲烷以二氧化碳还原型微生物成因为主,少量为混合气,海槽东南部可能是最有潜力的天然气水合物远景区。     

Manganese metalliferous sediments of the Deryugin Basin (Sea of Okhotsk): Chemical composition and geological setting

This paper reports the results of an investigation of the chemical composition and distribution of manganese-rich metalliferous sediments in the Deryugin Basin. They compose an upper sedimentary layer up to 30 cm thick within a strip up to 40 km wide and 180 km long in the central part of the basin along the East Deryugin suture zone bounding the Deryugin sedimentary basin to the east. The sediments are enriched relative to the regional background composition in Mn (by a factor of 35); Au; Ni; Zn; Co (by a factor of 3–5); and, locally, in Mo, V, Ba, Cu, Pb, and Hg. It was supposed that their formation was controlled by several processes: precipitation of Mn and some other trace elements from hydrothermal plumes of seawater that occasionally form above submarine hot vents in the northern part of the basin, precipitation from anoxic bottom waters at the eastern boundary of the Deryugin sedimentary basin, and early diagenetic migration of Mn into the surface sediments.     

Excitation of Under-Ice Seiches of a Sea Port of the Sea of Okhotsk

Doklady Earth Sciences - Multiannual observations (2009–2017) by means of autonomous seiche recorders have been conducted for marine seiches with one second discreteness in the boot basin for...     

Bubbled lava from the floor of the Sea of Okhotsk

A sample of bubbled lava raised from a submarine volcano in the Sea of Okhotsk was analyzed by means of electron microscopy and the ICP-MS technique. The outside of the sample is flecked with rounded micro- and macrocavities, and the inner part is characterized by a liquation structure. Along with this, the unstructured mass of the rock contains globular particles of nearly the same diameters as the cavities. The lava is close to andesites and volcanic ashes of Kamchatka Peninsula in the macro- and microelemental composition but different in the somewhat increased content of barium, strontium, lithium, niobium, tungsten, uranium, and thorium. It is suggested that the cavities were formed during the eruption of the submarine volcano owing to contact of the boiling gas-saturated lava with seawater accompanied by the ejection of ash, which was spread by marine currents over long distances.