В статье приводится краткий обзор результатов исследования аутигенных моносульфидов железа - магнитного грейгита и немагнитного макинавита - в отложениях двух районов Мирового океана. Оба эти минерала участвуют в образовании микро- и макроконкреций, что делает их более устойчивыми и позволяет участвовать в процессе диагенеза. Грейгит весьма широко распространен в восстановленных четвертичных осадочных отложениях. Его обнаружение в осадках дает возможность реконструировать диагенетические процессы на дне морей и океанов.

Vivianite, an authigenic mineral from the phosphate class, was discovered in Kara Sea bottom sediments for the first time. Similar finds of vivianite were previously known only for the outer shelf of the Laptev Sea, the northern Barents Sea, and the eastern White Sea. Its presence in the subsurface sedimentary strata indicates desalinization of the surface layer of the sea. Core 7444, sampled in a tectonic depression in the Kara Sea during the first stage of cruise 89 of the R/V Akademik Mstislav Keldysh (2022), uncovered Holocene sedimentary strata up to 6.19 m thick. Coarse-silty and sandy vivianite formations are found throughout the entire core, starting from 0.11 m. Vivianite was investigated by a set of methods: optical microscopy, X-ray diffraction, and scanning electron microscopy with energy dispersive spectroscopy. The morphology, microstructures, and chemical composition of vivianite formations have been studied. Three morphological types of these formations have been identified: micronodules and their intergrowths, crystalline aggregates and their intergrowths, and tubular aggregates.

The content of sediment-forming minerals in two cores from the eastern (ANS45-37) and western (ANS45-48) parts of the valley of the Vema Fracture Zone is studied using semiquantitative XRD analysis of bulk powder sediment samples. The mineral composition of deep-sea sediments from the Amazone Cone is also analyzed for comparison. It appeared that the average composition of the terrigenous component of both cores (according to prevailing quartz, secondary mica, plagioclase and potassium feldspar, as well as smectite, chlorite, kaolinite, illite) is quite similar and approximately corresponds to the composition of sediments from the Amazon Cone. The ratio of four clay minerals suggests supply of terrigenous material to the Amazon and Orinoco due to erosion of the Andes and humid tropical weathering in the lower courses of the rivers with further transport of the suspended load to the ocean. This material was transported to the valley of the Vema Fracture Zone due to interplay between gravitational flows from the South American continental slope and current of Antarctic Bottom Water. In addition, data on biogenic calcite (planktic foraminiferal tests, nannofossils) and opal A (radiolarians, sponge spicules) have been obtained. In the study area, several authigenic (diagenetic) minerals are identified. In particular, siderite and greigite are first found in the sediments from the Vema valley and Amazon Cone, respectively.

Lithological-mineralogical studies of bottom sediments in the northwestern shelf of the Black Sea using modern methods made it possible to diagnose a mineral complex reflecting the features of Holocene sedimentation and marking the stage of early diagenesis. The study of the material composition of bottom sediments in general, as well as diagnostics of the authigenic mineral complex, including gypsum, pyrite, and Mg-calcite, was carried out by X-ray powder diffractometry, as well as by microscopic methods, including optical and scanning electron microscopy. A genetic relationship of pyrite diagnosed in sediments with diagenetically altered remains of diatoms of the genus Amphitetras was revealed.

This paper, devoted to the mineral composition of ore-bearing sediments in the Pobeda hydrothermal cluster in the Mid-Atlantic Ridge (MAR), is a continuation of previous studies (Gablina et al., 2021). Rare zinc minerals (zinc phosphates, zincite, willemite, gahnite(?), and Zn-forsterite) are described. Most of these minerals were first established in bottom sediments of the MAR. The studies were carried out by several methods: scanning electron microscopy, X-ray spectral microanalysis, X-ray diffractometry, Raman spectroscopy, and electron backscatter diffractometry.

Ferromanganese (Fe-Mn) crusts in the ocean accumulate significant amounts of strategically important elements necessary for the development of high technologies. The recent study of Fe-Mn crusts shows that they noticeably vary in different oceans, and the purpose of this work is to compare the composition of Fe-Mn crusts from the Arctic and Atlantic oceans to reveal their similar features and differences and to associate them with a specific sedimentation environment. The chemical and mineral composition of Fe-Mn crusts from Knipovich Ridge located in the Arctic Ocean and from Brazil Basin in the Atlantic Ocean have been studied. Published data were used to increase the reliability of the conclusions. The Arctic Ocean crusts show specific characteristics such as low content of manganese, cobalt, and cerium and a high content of detrital material (Al), lithium, arsenic, thallium, and thorium. Previous data on high vanadium content are not confirmed. Low manganese content and the Mn/Fe ratio in the Arctic Ocean crusts negatively correlate with the accumulation of ice-rafted detrital material (Al is used as an indicator). This relationship indicates that the main difference of the Arctic Ocean crusts in comparison to the Atlantic Ocean crusts is associated with the fact that rocks supplied with ice are not equilibrated with seawater and contain Fe2+. The latter reduces manganese from MnO2 during the halmyrolysis, lowering the Mn/Fe ratio in the crusts.

Mineralogical, geochemical, and isotopic studies of the Fe–Mn crust collected in the Jan Mayen vent field area have been carried out for the first time. The crust (about 3 cm thick) has a distinct microstratified structure, sharp contact with the underlying volcanic substrate, and colloform Fe and Mn oxyhydroxides at its bottom. The crust is composed mainly of Mn oxyhydroxides: birnessite and buserite with an impurity of volcanic glass. As follows from the layer-by-layer study of the crust, the Mn content increases by 3–10 times from bottom to top, whereas Fe and REE decrease in the same direction. The samples are marked by a positive Eu anomaly (Eu/Eu NASC 1.08–1.41). Ce/Ce NASC is 0.89 ± 0.05. 87 Sr/ 86 Sr in the crust’s lower and middle layers is within 0.70621–0.70713, while ε Nd reaches 5.6–6.2. These parameters are 0.70740 and –0.1, respectively, in the uppermost layer of the crust. The REE composition, positive Eu anomaly, high ε Nd values, and low 87 Sr/ 86 Sr ratios in the crust are indicative of the fact that the ore material mainly originated from hydrothermal solutions. Changes in the Sr and Nd isotope characteristics and REE composition in the crust layers are due to a decrease in the hydrothermal material contribution as the crust grew at a high crust deposition velocity in the Jan Mayen vent field area.

The paper presents the mineral and chemical compositions of carbonate, metalliferous, and ore-bearing sediments developed within the Pobeda ore cluster based on the materials of stations 37L244g, 37L245g, and 37L184k by the chemical, optical, electron microscopic, electron probe, and X-ray methods. The compositions are compared with those of background biogenic carbonate sediments developed beyond the hydrothermal cluster. The results revealed that the hydrothermal activity zone is marked by various types of mineral and geochemical zoning: (1) increase in the ore element concentration downward the sediment section leading to a downsection change of carbonate sediments by the ore-bearing variety (St. 37L184k); (2) layer-by-layer enrichment of sediments with ore components (St. 37L244g); and (3) confinement of concentration zones to the roof, middle part, and bottom of sedimentary deposits (St. 37L245g). The relationship of various types of mineral and geochemical zoning with the physical and chemical parameters of interstitial waters in the metalliferous and ore-bearing sediments is considered.

The paper presents data from grain size and mineralogical analyzes of surface bottom sediment samples obtained on several cruises of the R/V Akademik Mstislav Keldysh (2016–2018) from different parts of the Barents Sea. Pebble and gravel material is found in surface sediments in the form of impurities scattered throughout the sea. Such a chaotic distribution pattern is apparently associated with ice separation. Coarse material is most common in the Barents Sea off the coast of the Kola Peninsula, off the coast of Novaya Zemlya, Spitsbergen, where it accumulates due to coastal abrasion. In addition, a fraction >1 mm is widespread at depths where fine fractions are stirred and leached. The most common sediments in coastal shallow water are sands. Sands (0.1–1 mm) are widespread in the southern and southeastern regions of the sea, in the region of the Pechora polygon, the Kaninsky shallow water, the Kola Peninsula, and in the northwest, off the coast of Svalbard. With increasing depth, the sands are replaced by mixed sediments with a low admixture of pelite. Pelitic sediments are prevalent in the central part of the sea. Precipitation with a pelitic fraction (<0.01 mm) of more than 50% occupy about 70% of the Barents Sea. They are widespread in deep-sea hollows and trenches, as well as in the numerous fiords of the North Island of Novaya Zemlya and Franz Josef Land. Surface sediments have a predominantly terrigenous composition; only at the border with the Norwegian Sea the proportion of biogenic material increases. The mineral composition of sediments is dominated by quartz and feldspars, clay minerals are mainly represented by illite, smectite and kaolinite.

The paper presents the first results of a study of seasonal variations in the grain size distribution and mineral compositions of suspended particulate matter (SPM) of the Northern Dvina River. The SPM samples were collected every month during 2016–2017 at the outlet of the Kuznetchiha arm to Dvina Bay of the White Sea. The grain size fractions were separated by Petelin’s water-mechanical method with retention of fractions for subsequent analyses using an electron microscope, energy-dispersion microanalyzer, and X-ray difractometer. The results demonstrated that the pelitic and subcolloidal fractions predominated in the grain size distribution of river SPM, with subordinate coarser fractions. Seasonal variations in the SPM concentration and the total amount of detrital and clay minerals are influenced by river water discharge and achieved a maximum in high water periods (spring flood and partly at the end of summer–autumn heavy rains). The subcolloidal fraction in the March sample stands out in the fine fraction distribution. Its share in this sample was the highest among these fractions throughout the year. The reason is probably related to the highest content of fine dispersed detrital minerals in the fraction. The question of why this is encountered only in March remains open.

The article discusses the preliminary results of plume and bottom sediment studies of the Trollveggen hydrothermal vent field based on data from cruise 68 of the R/V Akademik Mstislav Keldysh. The hydrothermal vent field is located east of the axial zone of the slow-spreading Mohn Ridge near the Jan Mayen hotspot at a depth of about 550 m (71°18′ N, Norwegian–Greenland Basin). The hydrothermal vent field plume was characterized by a weak distribution in the water column; temperature, density, and salinity anomalies; a moderate methane concentration; and a low concentration of suspended particulate matter near the bottom. The enrichment of bottom sediments in barium, strontium, and some sulfide-forming elements (zinc, lead, copper, and molybdenum) was shown. Two mineral assemblages of hydrothermally modified bottom sediments were revealed: pyrite and barite–marcasite. The temperature of hydrothermal fluids was established by thermal and cryometric studies of gas–liquid fluid inclusions in barite (128–260°С); the FeS–ZnS equilibrium diagram of sulfide minerals was also used (130–290°С). Our data were close to direct fluid temperature measurement data [28]. We compared the hydrothermal mineralization of the Trollveggen vent field and earlier studied fields of the Mid-Atlantic Ridge located near the Azores hotspot. As a result, we confirmed the influence of ocean depth and PT conditions on the formation of hydrothermal deposits.

Подводный хребет Ширшова представляет собой самостоятельную систему терригенной седиментации, геоморфологически изолированную от придонных потоков поступления терригенного материала в глубоководную котловину Берингова моря. Это позволило на его примере исследовать фоновую гемипелагическую седиментацию тонкодисперсной терригенной взвеси из водной толщи и осаждение более крупнозернистого материала ледового разноса в западной части глубоководной котловины. Гранулометрический и минеральный состав послеледниковых отложений хребта Ширшова изучен в колонках SO201-2-85KL и SO201-2-77KL, отобранных в локальных впадинах центральной и южной частей хребта, соответственно. Статистическая обработка непрерывных гранулометрических распределений (ГР) терригенной составляющей послеледниковых отложений методом моделирования конечных элементов (КЭ) выявила смешивание трех КЭ в реальном гранулометрическом составе осадков из двух колонок. КЭ-1 и КЭ-2 отражают гемипелагическую седиментацию без влияния и с влиянием придонных течений, соответственно, а КЭ-3 с модой в области мелкозернистого песка характеризует ГР материала ледового разноса. Реконструированы механизмы поступления терригенного материала на хребет Ширшова ‒ адвекция взвеси в составе поверхностных и промежуточных водных масс и ледовый разнос. Оценена относительная роль обоих механизмов терригенного осадконакопления в условиях изменчивых скоростей придонных течений для интервалов максимума последнего оледенения, ранней дегляциации, события Хайнриха 1, беллинга/аллереда, позднего дриаса и раннего голоцена. Выявлена зависимость гранулометрического состава терригенной составляющей осадков от климатических изменений, ледовитости, путей дрейфа и условий таяния припайного льда, подвижности придонных вод. Над южной частью хребта во второй половине события Хайнриха 1, вероятно, существовали условия с плотным скоплением дрейфующих льдов или сплошным ледовым покровом. При малой подвижности придонных вод происходило только подледное гемипелагическое осаждение тонких фракций из фонового резерва взвеси. Резкое сокращение поступления материала ледового разноса реконструировано для интервала потепления белинга/аллереда. Придонные течения влияли на осадконакопление в центральной части хребта в течение всей дегляциации (кроме второй половины события Хайнриха 1), а в его южной части — в беллинге/аллереде, позднем дриасе и раннем голоцене.

The submarine Shirshov Ridge is an independent system of terrigenous sedimentation, which is geomorphologically isolated from bottom terrigenous influx into the deep-water basin of the Bering Sea. Using the ridge as example, we studied background hemipelagic sedimentation of the finely dispersed terrigenous suspended material from water column and deposition of the coarser grained ice-rafted material in the western part of the deep-water basin. The grain-size and mineral composition of postglacial sediments of the Shirshov Ridge was studied in cores SO201-2-85KL and SO201-2-77KL taken from local basins in the central and southern parts of the ridge, respectively. Statistic treatment of uninterrupted grain-size distributions (GD) of terrigenous component of the postglacial sediments by end-member (EM) modelling revealed that the grain-size distributions of terrigenous sediments from two cores are determined by the mixing of three EMs. EM-1 and EM-2 reflect the hemipelagic sedimentation with and without bottom currents influence respectively, while EM-3 with mode at fine-grained sand characterizes GD of the ice-rafted material. Reconstructed mechanisms of terrigenous influx on the Shirshov Ridge involve advection of the suspended matter with surface and intermediate water masses and ice-rafting. The relative role of both mechanisms of the terrigenous sedimentation under the influence of varying bottom current velocities for intervals of Last Glacial Maximum, early deglaciation, Heinrich event 1, Bølling–Allerød, Younger Dryas, and Early Holocene is estimated. It is ascertained that the grain-size distribution of terrigenous component is defined by climate variations, sea ice coverage, sea ice drift pathways, conditions of fast ice melting, and mobility of bottom waters. High concentrations of drifting ice or seasonal sea ice cover likely existed above the southern part of the ridge during the second half of the Heinrich 1 event. The low mobility of bottom waters facilitated only the subice hemipelagic sedimentation of fine fractions from the background reserve of suspended material. A sharp reduction of ice-rafted flux was reconstructed for the Bølling–Allerød warming interval. Bottom currents affected sedimentation in the central part of the ridge during the entire deglaciation (in addition to the second half of the Heinrich 1 event), and in the southern part during the Bølling–Allerød, Younger Dryas, and Early Holocene.

The paper presents the results of lithological, mineralogical, and geochemical studies of bottom sediments in the central part of the South Caspian Basin. A complex of analytical methods was used to identify authigenic minerals from groups of sulfates, carbonates, and sulfides; study their forms of crystals and aggregates and their composition; and determine the distribution pattern in bottom sediments. The lithological and geochemical data were used to identify the characteristic property of authigenic mineral formation processes in the central part of the South Caspian Basin under hydrogen sulfide contamination conditions.