The aim of this work is to elucidate the specifics of recent sedimentation in the Chukchi Sea, based on the study of the material composition of Late Holocene bottom sediments. Analytical methods included grain size and mineralogical analyses. The results of 210Pb and 137Cs dating were used. The sediments are clayey silt and silty clay containing sand admixture and single gravel grains and pebble. The content of coarse-grained material increases slightly in the upper parts of the studied sections. This is probably due to the greater contribution of ice rafting to the recent Chukchi Sea sedimentation as a result of climate warming. The ultrafine- and fine-grained (0.25-0.05 mm) sandy material is dominated by light-fraction minerals. Volcanic glass was discovered in the sediments sampled in the southern and central areas of the Chukchi Sea. It might have been transported from the volcanoes of Alaska, the Aleutian Islands, and the Kamchatka Peninsula through the Bering Strait by the Pacific currents directed from south to north. The sediments collected in the southern, central, and northern areas of the Chukchi Sea differ in grain size and mineral composition. This is probably due to their remoteness from the coastline and provenance areas and is also caused by different rates of sedimentation.

The third finding of ikaite in Holocene sediments of the Chukchi Sea is described. Based on the results of a comprehensive study (mineral, chemical, and isotopic composition), a conclusion is made about the formation under low temperatures with the participation of carbon from the oxidation of organic matter and methane.

Ore crusts with a germanium content of up to 96 ppm were discovered in the Sea of Japan. This is tens of times higher than the clarke of the Earth’s crust. Germanium-rich crusts were dredged together with intermediate and felsic volcanic rocks. The crusts are composed predominantly of iron oxyhydroxides (goethite) and contain germanium in the dispersed state.

The paper presents a brief overview of the results of integrated geological, geophysical and oceanographic studies for the period 2017–2023, for which interregional generalizations were made on some promising areas of study of underwater mineral resources and the environment. The data on geological underwater objects, in particular, manganese ores of the Sea of Japan and the Sea of Okhotsk and adjacent water areas; rare-earth ores of the Tomtor ore cluster, ancient and modern coastal-marine placers of the Laptev Sea coast are presented; barite ore occurrences “Barite Hills” (in the Sea of Okhotsk); ferromanganese formations of the Eastern Arctic shelf of Russia; coastal marine placers of the shelf and coast of the Far Eastern seas, including gold-bearing placers. including gold-bearing placers of the shelf zone of the south of Primorye and north of Sakhalin, titanomagnetite placers of the Kuril Islands, gold-bearing placers of the North Sakhalin Plain and others. Direct signs of hydrocarbons were obtained in areas previously considered unpromising (including the South China Sea), gas hydrate accumulations were mapped and studied in the Sea of Okhotsk and the Sea of Japan, prospecting for gas hydrates in the Bering Sea was prepared, and comparative studies of hydrate-bearing capacity of the marginal seas of the NW Pacific and the Indian Ocean were carried out. The main features of the distribution of lithologic and gas-geochemical indicators of hydrocarbon gases in bottom sediments of the southwestern sector of the East Siberian Sea, which is the least studied in terms of oil and gas content, were studied. Based on the data of gas-geochemical studies, the prospects of oil and gas content of the eastern shelf of the Arctic were assessed. The results of geomicrobiological studies in the seas of the Far East region are described. In some cases deepsea sediments themselves (peloid-like sediments, etc.) appear to be a separate huge mineral resource. At present, the “continent-ocean” transition zone and neutral waters can become the most important source of replenishing the mineral resource base of these mineral components. The presented research corresponds to the main objectives of the GEOMIR project of the national action plan within the UN Decade of Ocean Sciences for Sustainable Development (2021–2030) and was carried out mainly in accordance with the directions of the state assignment. Studies of gas hydrates were carried out within the framework of the WESTPAC working group “Gas hydrates and methane fluxes in the Indo-Pacific region” (CoSGas, 2021–2024), established on the initiative and under the leadership of Russia.

A modified gravity corer (MGC) for more efficient and high-quality sediment core sampling is considered. Such design elements as the core catcher, section muff joints, the weight, and loop have been modified; the crown and locking plate have been removed. As a result of comparative testing in the South Chukchi Basin of the Chukchi Sea, it is shown that the MGC sampled 30

--We studied the distribution of gold, silver, and platinum group elements (Pd, Pt, Rh, Ir, and Ru) in two bottom sediment cores of the southern Chukchi Sea. It is shown that the Holocene pelite-silty sediments with an age of up to 4.0 ka BP are significantly enriched in these elements, except for Ru and Rh, relative to their clarkes. Native silver minerals were found in all samples by probe microanalysis, whereas gold minerals were revealed only in the surface layer of the sediment core closest to the Chukchi Sea coast. Multicomponent statistical analysis of the chemical composition and grain size of the sediments and the content of organic matter in them has led to the conclusion about the accumulation of clastogenic and chemogenic forms of precious metals. The abnormally high content of gold (0.3 ppm) in the recent sediments near the Chukchi Peninsula coast might be due to its additional removal from the continent as a result of the placer mining there.

The first case of hydrothermal brecciated crusts composed of goethite with quartz veinlets is described for the Sea of Japan.

Изучено распределение золота, серебра и элементов платиновой группы (Pd, Pt, Rh, Ir, Ru) в двух колонках донных осадков южной части Чукотского моря. Установлено значительное обогащение этими элементами, за исключением Ru и Rh голоценовых пелит-алевритовых осадков с возрастом до 4 тыс. лет, относительно их кларка в земной коре. При электронно-микрозондовом анализе самородные минералы серебра встречены по всем пробам, минералы золота только в поверхностном слое осадков колонки, наиболее близкой к побережью Чукотки. При анализе данных по химическому составу, гранулометрии, содержания органического вещества с использованием методов многокомпонентной статистики обосновано накопление благородных металлов в кластогенной и хемогенной формах. Аномально высокое содержание золота 0.3 г/т в современных осадках вблизи побережья Чукотки, возможно, обусловлено дополнительным выносом его с материка из-за разработки россыпных месторождений на суше. We studied the distribution of gold, silver, and platinum group elements (Pd, Pt, Rh, Ir, and Ru) in two bottom sediment cores of the southern Chukchi Sea. It is shown that the Holocene pelite–silty sediments with an age of up to 4.0 ka BP are significantly enriched in these elements, except for Ru and Rh, relative to their clarkes. Native silver minerals were found in all samples by probe microanalysis, whereas gold minerals were revealed only in the surface layer of the sediment core closest to the Chukchi Sea coast. Multicomponent statistical analysis of the chemical composition and grain size of the sediments and the content of organic matter in them has led to the conclusion about the accumulation of clastogenic and chemogenic forms of precious metals. The abnormally high content of gold (0.3 ppm) in the recent sediments near the Chukchi Peninsula coast might be due to its additional removal from the continent as a result of the placer mining there.

This paper describes an approach assuming that already in the sea, based on the express analysis of visually similar cores of Arctic Holocene sediments and their comparison with dated and studied in detail cores of the regional sediments, it is possible to select a material that is promising for sequence stratigraphic correlation and paleoreconstructions. The range of lithological, colorimetric (CIE L*, CIE a*, and CIE b*), geophysical (magnetic susceptibility), and geochemical (Fe/Rb, Mn/Rb, and Ti/Rb) parameters is analyzed. The most informative characteristics include the CIE b* color coordinate, magnetic susceptibility, and Fe/Rb.

Deciphering the origin of sedimentary material in the Arctic can contribute to a deeper understanding of modern transport and sedimentation processes. Here, the application of rare earth elements (REEs) is particularly promising, as they can serve as indicators of sources as well as chemical and physical conditions and processes. This study aimed to determine the distribution of REE sources in the bottom sediments and the forms of their occurrence on the East Siberian Arctic Shelf. The concentrations and distributions of the REEs and major and trace metals, grain size, and mineral composition of 72 surficial sediment samples and two sediment cores that were collected from the Laptev and East Siberian seas were studied. Increasing REE content, the predominance of light REE, and close correlation with Zr, Nb, Y, Sc, and Ti were revealed in the Laptev and western East Siberian sea sediments in the zone of influence of the Lena River runoff. The source of the REEs was the eroded Yedoma complex along the coast. The REE content in the sub-colloidal fraction of the sediments was comparable to the REE concentration of the bulk bottom sediments and varied in the East Siberian Sea from 104 to 220 mg kg -1, with the maximum content around the submarine valley of the Indigirka River, in the Laptev Sea, ranging from 124 to 197 mg kg -1. The findings could be used to study ice dynamics and to conduct lithostratigraphic and paleoceanographical reconstructions of the Central Arctic.

The distribution of rare earth elements (REEs) has been studied for the first time in different morphotypes of ferromanganese formations (FMFs) from the East Siberian Sea, namely, ferruginous and ferromanganese crusts, discoid nodules, and biomorphoses. The FMFs were formed at different distances from the land and, accordingly, from the main sources of sedimentary material during (sub)oxic diagenesis. Seaward, with an increase in the oxidation of sediments, primarily because of reducing sedimentation rates, FMFs, against a rising manganese content in them (Mn from 0.09% to 12.34%, Mn/Fe from 0.01 to 1.15), show a decrease in the total REE content (ΣREE from 166.90 ppm to 96.86 ppm), depletion in cerium (Cean from 0.90 to 0.71), and enrichment with middle REEs. Due to the rapid growth of FMFs, which should be faster than sedimentation rates, reactive REE species do not have time to accumulate; therefore, REE total content in FMFs is everywhere lower than in sediments.

Manganese crusts, composed of manganite with an admixture of pyrochroite and quartz, are revealed for the first time in the Sea of Japan. According to a combination of features, these are low-temperature hydrothermal mineral formations that appeared on the slope of the South Yamato Ridge at a depth of no more than 1300 m under conditions of oxygen deficiency.

Проанализированы геохимические и минералогические аспекты распределения редкоземельных элементов (РЗЭ) в железистых образованиях (ЖО) и донных осадках юго-восточной части моря Лаптевых. Среди ЖО преобладают биоморфозы по трубкам полихет. Общее содержание и распределение РЗЭ в ЖО складывается из соотношения рудного и нерудного вещества. Рудное вещество представлено в основном гидроксидами железа (лимонит). Оно сформировалось в ходе субокислительного диагенеза, усиленного процессами биотурбации, и определяет в ЖО некоторый избыток средних РЗЭ и дефицит церия (Ceан - 0.94). Нерудное вещество поступает в ЖО из терригенных осадков и имеет (алюмо)силикатный состав. Оно определяет в ЖО содержание скандия и является источником зерен минералов РЗЭ, среди которых преобладает монацит-(Ce). Для осадков характерно общее подобие составу РЗЭ в сланцах и во взвеси р. Лена, впадающей в море Лаптевых, при небольшом избытке легких и средних РЗЭ и величине цериевой аномалии, практически равной единице (Ceан - 1.06). В осадках минералы РЗЭ тяготеют к фракциям мельче 63 мкм. Высокое содержание в осадках органического вещества (Сорг - до 2.15 %), имеющего преимущественно терригенный генезис (ОВтер - до 85 %), объясняет дефицит кислорода и общее вялое протекание процессов диагенетического минералообразования со слабым накоплением в ЖО микроэлементов, включая РЗЭ. Суммарное содержание РЗЭ в ЖО ниже, чем в осадках, и составляет в среднем 173 против 206 г/т. The geochemical and mineralogical aspects of the distribution of rare-earth elements (REE) in ferruginous deposits (FD) and bottom sediments of the southeastern Laptev Sea are analyzed. The FD are dominated by biomorphs developed after polychaete tubes. The REE patterns depend on the proportion of ore and non-ore substances. The ore substance is represented mainly by iron hydroxides (limonite). It is a product of suboxic diagenesis enhanced by bioturbation and determines the slight enrichment of FD in MREE and cerium deficiency (Cean = 0.94). The non-ore substance comes from terrigenous sediments and has an (alumino)silicate composition. It controls the scandium content and is the source of REE mineral grains, among which monazite-(Ce) prevails. The sediments demonstrate a common similarity in REE patterns to shales and suspended material transported to the Laptev Sea by the Lena River, with elevated LREE and MREE contents and the value of Ce anomaly almost equal to unity (Cean = 1.06). In the sediments, REE minerals occur mostly in the silt fraction (<63 μm in size). The high content of organic matter (Corg of up to 2.15%) of predominantly terrigenous origin (OMter of up to 85%) in the sediments explains the oxygen deficiency and weak diagenetic mineral formation with low accumulation of trace elements, including REE, in the FD. The total REE content in the FD is lower than that in the sediments (on average, 173 ppm against 206 ppm).

Ferruginous (goethite) mixed-type hydrothermal–hydrogenetic crusts, which were found in the Sea of Japan for the first time, are described. Compared to manganese (todorokite, birnessite) mixed-type hydrothermal–hydrogenetic crusts, which are common in the Sea of Japan, ferruginous crusts were probably formed under higher temperatures and closer to the hydrothermal fluid outlets on the seafloor. The substance that hydrogenetically precipitated to the crusts from seawater after the cessation of hydrothermal process is identified by the high contents of Th and rare earth elements and also by the positive Ce and negative Eu anomalies.

The distribution of rare-earth elements (REEs) in ferromanganese deposits (FMDs) from the southeastern Laptev Sea is considered. The ore part of FMDs consisting mainly of iron hydroxides (limonite) results from the process of suboxic diagenesis enhanced by bioturbation. It is responsible in FMDs for the deficiency in Ce and some enrichment in middle REEs (MREEs). The (alumino)silicate part of FMDs is genetically related with bottom sediments, corresponds to their REE composition, and most likely controls the scandium content. Because of the high formation rate of hydroxides, the total REE content in FMDs is lower than that in bottom sediments.

A new method of quantitative determination of color using an original photodevice is presented for marine sediments, which are a specific geological object. The advantages of the photodevice over the main color-measured tool (colorimeter) are shown for the example of numerous sedimentary columns from the Pacific and Arctic oceans.

Выполнена первая полуколичественная и качественная оценка наложенной (поствулканической) рудной минерализации основных типов вулканических пород - окраинно-континентального, пострифтового и щелочного, - слагающих в Японском море подводные возвышенности. Главное внимание сосредоточено на минеральных формах выделения цветных, благородных и редких металлов. Максимально ярко минерализация проявлена в породах пострифтового типа, что объясняется флюидонасыщенностью исходной магмы, длительностью вулканических и поствулканических процессов.

Представлены данные минералогического анализа тонкого и мелкого песка в составе осадков, накопленных в южной части Чукотского плато за четвертичное время. Рассмотрены ассоциации и распределение по разрезу породообразующих и акцессорных минералов, их связь с другими характеристиками. Выявленные минералогические особенности, обусловленные климатическими изменениями — периодами потепления и похолодания, могут быть использованы в решении ряда генетических вопросов, стратификации, палеореконструкциях.