This article presents new data from geochronological study the lake-bog organic-rich layer from of the “Ilya Prorok” sequence (Upper Volga Basin, Tver Region) that is a one of the reference sections located on the Russian Plain. Ideas concerning the age and climatic conditions of these organic-mineral deposits formation changed significantly over the long history of their study. As a result, the viewpoint about the belonging of this layer to the Likhvin time began to prevail. However, it is still unclear with which marine isotope-oxygen stage (MIS) the Likhvin interglacial can be compared. According to the paleobotanical study of the lake-bog from the Ilya Prorok section, it was confirmed that the lower part of the lake-bog layer can be attributed to the warm phases of the Likhvin interglacial, while its upper half was deposited during the transition to cooling after the interglacial period. For the first time, the radioisotope age of the buried lake-bog deposits of the reference section “Ilya Prorok” have obtained. According to the data of direct 230Th/U dating, the formation of the sequence probably began no earlier than ~ 326–260 Kyr ago. The 230Th/U age of the buried peat bog from its upper half, according to the results of applying the isochronous approximation, can be correlated with the interval ~256–225 Kyr ago. According to these data, the Likhvin deposits were formed no earlier than MIS-9.

The main goal of this study was to elucidate the chronostratigraphic position of the sediments of lacustrine-bog stratum from the Ch-14 section located in the sub-latitudinal sector of the Chernaya River in the north of the Bolshezemelskaya tundra. This study presents data on their numerical age and time of their formation, obtained by the parallel 230Th/U and 14С dating of organic-rich layers. According to the results of spore-pollen analysis obtained earlier, the lacustrine-bog sediments were attributed to the Byzovaya (Middle Valdai) interstadial, together with the lake and alluvial deposits from the Ch-3 and Ch-4 sections in the same sector of the Chernaya River. The 230Th/U and 14C age data are in good agreement with each other, especially for the lower boundary of the lacustrine-bog sediments of the Ch-14 section. The time range of the lacustrine-bog stratum accumulation is estimated to be approximately 13.7–13.3 to ~12.0 thousand years ago. Thus, its formation (10.5–6.5 m layer) did not occur in the Middle Valdai, but in the Late Valdai time from the beginning of Allerød to the beginning of the Younger Dryas cooling. It has been suggested that a certain delay of late glacial climatic events took place in the Bolshezemelskaya tundra compared with their age-related estimation by the Greenland isotope-oxygen stages. For the first time, the isochronous approximation approach was applied to obtain the 230Th/U age of such young terrestrial organic-rich deposits. Earlier this approach was usually used in dating similar sediments not younger than MIS-3. The geochronological results presented in this paper allow us to recommend the 230Th/U method for determining the age of late glacial organic-rich deposits and climate events correlated with them.

A new reference section of the Okhotsk seaside of Kamchatka in the Mitoga 2 River area is studied and dated for the first time (14C and 230Th/U). Sedimentary deposits were correlated with the previously known sections in the Khomutina‒Mitoga interfluve. It has been established that the sequence of “gray silts and clays” represents deposits of a large lake-type estuary, which began to swamp about 90–80 ka BP, and all sediments overlapping the silts began to form no earlier than 90 ka BP (second half of MIS 5). Deposits of a catastrophic collapse (clastic mass transport over about 100 km, area ≥1500 km2, volume ≥15 km3), which descended from the Balaganchik Ridge about 90‒80 ka BP, were identified. Two main facies were established: dispersed basal layer (“moraine-type loam” sequence) and landslide proper sediments (conglomerates). Valleys of the Bystraya and Plotnikova rivers were blocked by a collapse, resulting in the formation of a large dammed lake. The catastrophic drainage of the lake could occur about 37 ka BP. Deposits related to the dam breakthrough are recorded between the Mitoga 2 River and Zuikovo Settlement on the Okhotsk coast.

A geochronological and mineralogical study on the seafloor massive sulfides from the Pobeda hydrothermal cluster at the Mid-Atlantic Ridge was carried out. To improve the reliability of geochronological data, the 230Th/U ages were measured for both the bulk samples and monomineral separates. The oldest age ca. 52 kyr within Pobeda-1 and ca. 107 kyr within Pobeda–2 fields have been obtained. Then, several episodes of hydrothermal activity were identified within both fields up to ca. 0.3 kyr ago and up to ca. 4.3 kyr ago, respectively.

ИнстИтут ИсторИИ матерИальной культуры ран россИйскИй государственный педагогИческИй унИверсИтет Им. а.И.герцена самарскИй государственный соцИально-педагогИческИй унИверсИтет

This article presents the results of a comprehensive geochronological study of organic-rich sediments lying at the base of the sand suite in the well-known reference Belyi Yar II section on the left bank of the Irkut river (Tunka depression, Southwestern Cisbaikalia). It was found that in the 1960s, a pack of lake-marsh sediments from the lower part of the section was assigned to the upper Eopleistocene, and the overlying sands to the Samarovo period of the Middle Pleistocene. Later, based on the first 14C datings, the stratigraphy of these sediments was revised. The lower part of the sediments was attributed to the Karginsky time, and the overlying sands to the Sartanian glaciation. However, the questions concerning the genesis, age and conditions of formation of these sediments remain controversial. In particular, the individual dates of 14C differ greatly from one another; therefore, they require further verification. A renewed study of the lower part of the Belyi Yar II section discovered peat and gyttjas deposits of alluvial origin. It was shown that their numerical age is beyond the 14C dating method limits. Paleobotanical data showed that the gittya was formed in conditions of a relatively warm and humid climate, and the overlying layers accumulated in the cooling and more xerophytic condition. Evaluation of the 230Th/U isochronous age of these organogenic deposits, combined with palynological data, suggested that the bottom of the sand layer in the Belyi Yar II section was not formed during the Karginsky time (MIS 3), as was thought previously, but during MIS 5. The gittya could have formed during MIS-5c, whereas the overlying peat layers formed, possibly, at the transition to MIS-5b.

Perspectives of the 230Th/U method for dating the fossil bones of mammoths, widespread in sediments of the Arctic region, are considered. Determination of uranium and thorium contents in well-preserved mammoth bone samples with known radiocarbon age was carried out and the prerequisites for the 230Th/U method were tested. It was revealed that the external and middle layers of bones can be geochemical barriers that make it difficult for dissolved uranium to enter the internal layers during post-sedimentation time. Thus, the internal layers can be attributed to conditionally closed radiometric systems. In some cases, 230Th/U age of these layers is similar to radiocarbon data. 230Th/U age in the range of 100 thousand years was obtained for the sample with the direct radiocarbon age. The results suggest that using the 230Th/U method for determining the age of mammoth bones is possible under certain conditions.

Recent revision of the eastern boundary of the last glaciation of Eurasia opened new perspectives in the search of the paleopedological records in the north of Eastern Europe and Western Siberia. We studied paleosol-sedimentary sequences in the Upper Volga and Middle Ob basins as a regional paleoecological record for the Late Pleistocene thermochrons. Two key sections Cheremoshnik and Belaya Gora containing MIS3 and MIS5 paleosol units and additional section Koskovo 2 with polycyclic MIS3 paleosol were investigated. Their timescale are based on C14 and U/Th datings as well as on stratigraphic and paleobotanical correlations. Macro-, meso- and micromorphological observations together with fossil insects and plant macrofossil were used as paleoenvironment proxy. MIS3 paleosols show abundant redoximorphic and cryogenic features that allow interpreting them as gleyic Cryosols. Sub-fossil insects and plant macrofossil reflect the cold climate conditions. Three incipient Ah horizons in Koskovo 2 pedocomplex point to multiple phases of pedogenesis, correlative to the MIS3 paleosol levels in different sections of the Eurasian loess belt and to the major interstadials of the Middle Pleniglacial of the NW Europe MISS paleosols are also characterized by gleyzation and peat accumulation, in this case we suppose geomorphological control on hydromorphic pedogenesis; however paleosol in Belaya Gora has clear signs of polygenesis including the phase of clay illuviation. Insect and plant remains from the lower paleosol level of the Belaya Gora section show the transition from cold (terminal phase of MIS6) to warm first, and then to a moderately cold climate (within MIS5). The obtained results contribute to understanding of soil and landscape zonality in the largest plains of Eurasia mostly during the warm phases of Late Pleistocene. (C) 2018 Elsevier Ltd and INQUA. All rights reserved.

For the first time, numerical radioisotope age were obtained for the “cross-laminated sandy” stratum, which is widespread in Neopeopleistocene reference sections of loose sediments from Central Kamchatka. Two peat layers, incorporated in the “cross-laminated sandy” stratum of the Yar Sredny, were studied. The results of their paired 230Th/238U and 14C dating are in good agreement with each other. According to the dating results, it was determined that the “cross-laminated sandy” stratum was deposited, apparently, in the range of about 50-40 thousand years ago, i.e. in the Late Pleistocene (MIS-3), and not in the Middle Pleistocene, about 400-300 thousand years ago, as previously thought.

Впервые получены количественные данные о радиоизотопном возрасте толщи “косослоистых песков”, широко распространённой в неоплейстоценовых опорных разрезах рыхлых отложений Центральной Камчатки. Исследованы два горизонта торфа, погребённых в толще “косослоистых песков” яра Среднего. Результаты изотопного датирования, проведённого разными методами ( 230 Th/ 238 U- и 14 С-), хорошо согласуются между собой. По итогам работ установлено, что, по-видимому, вся толща отлагалась в интервале около 50-40 тыс. лет назад, т.е. в позднем плейстоцене (МИС-3), а не в среднем, около 400-300 тыс. лет назад, как считалось ранее.

The first quantitative data on the radio-isotope age are presented for a sequence of cross-layered sands abundant in the Neopleistocene reference sections of loose sediments of Central Kamchatka. Two peat horizons buried in a sequence of cross-layered sands of Yar Sredny are studied. The results of 230Th/238U and 14С isotope dating are quite consistent. It is found that the entire sequence was probably deposited at 50–40 ka BP (Late Pleistocene, MIS-3) in contrast to the previously suggested age of 400–300 ka (Middle Pleistocene).

This article presents the results of a comprehensive geochronological study of gyttja deposits from a section of a terrace above a floodplain located on the right bank of the Ob River near the town of Kolpashevo. According to the 230Th/U dating, the age of the gyttja could be dated in the range of 110–95 kyr. The results of spore–pollen analysis suggest that the gyttja deposit was formed in the period of a wide distribution of middle taiga forest landscapes with the dominance of spruce; the climatic conditions were similar to modern ones. These events probably took place in the interstadial time during MIS-5c or at the end of Kazantsevo interglacial period.

Dating of late Pleistocene sediments remains a challenge in Quaternary chronology, due to the inherent limitations of the 14C and OSL methods. The 230Th/U radioisotope method is theoretically applicable to wood remnants contained within Pleistocene sediments, but few results have been pub-lished to date and in some cases, the age data are ambiguous. This paper tests the use of 230Th/U da-ting of fossil wood remnants dated earlier by radiocarbon method. We analyzed a buried larch trunk from a well-known stump layer in the Lipovka outcrop, located on the Tobol River bank in Western Siberia. The stump layer is preserved in situ. We determined the specific activities of U and Th iso-topes in samples of both modern pine and fossil larch and proposed a model for the incorporation and distribution of U and Th in the buried wood during aging. Complications related with the recognition of geochemical closed systems with respect to U did not allow obtaining completely reliable 230Th/U age. Despite this the 230Th/U age obtained for the uppermost heartwood sample and 14C ages of the same larch trunk and other wood and vegetation remnants gave consistent results. These age data in combination with previously obtained pollen data testify the stump layer formation during the late cooling stage of the Karganian time (MIS-3, Middle Valdai).

From the viewpoint of precision and reliability of radioisotopic dating, deposits whose quantitative age can be determined through several methods of geochronometry are of special interest. The mutually conforming finite 14 C and 230 Th/U dates of buried Neopleistocene organic deposits, taken from the Tolokonka section by the North Dvina River (100 km downstream from the city of Kotlas), have been obtained for the first time in Russia. The stratigraphical reference of these results to those obtained via the optically induced luminescence for upper and lower bedding layers has been established. The presented geochronometric data have allowed us to consider the age of oxbow lake organic deposits completely reliable and refer the time of their formation to the Tyrbei warming within the MIS-3. The applicability of the new version of the 230 Th/U method for dating of interglacial and interstadial deposits, for the purpose of solving the Middle and Late Neopleistocene chronostratigraphy issues, is confirmed.