V. Yu. Kuznetsov

Massive sulfide ores of the northern equatorial Mid-Atlantic Ridge

The optimal set of prospecting methods, including geophysical (geoelectrical), geological (mineralogical-geochemical), and hydrological observations, was developed during the long-term investigations of the sulfide mineralization in the northern equatorial zone of the Mid-Atlantic Ridge. The application of these methods made it possible to discover six massive sulfide deposits and considerably extend the boundaries of another two ore objects. The ores associated with ultramafic rocks are characterized by elevated Cu, Au, and Co concentrations. It is established that the ore formation was a multistage process that resulted in the accumulation of large deposits (over 10 million tons).

The first case study of 230Th/U and 14C dating of mid-valdai organic deposits

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 14C and 230Th/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 230Th/U method for dating of interglacial and interstadial deposits, for the purpose of solving the Middle and Late Neopleistocene chronostratigraphy issues, is confirmed.

Stratigraphy of bottom sediments in the Mendeleev Ridge area (Arctic Ocean)

602 Two age models are available for bottom sediments cored in the Arctic Ocean: “older” [1–5] and “younger” [6–9]. The first of them assuming very low sedimentation rates is based on interpretation of the magnetization vector in sediments and finds of partic ular stratigraphically significant microfossils (index species and assemblages). The replacement of the pos itive residual magnetization in sedimentary sections by the negative one, which was correlated with the boundary between the Brunhes and Matuayma paleo magnetic epochs, was considered as the main criterion for developing the “older” model [3]. The second model assuming higher sedimentation rates is based on amino acid dates obtained for tests of planktonic foraminifers, optically stimulated luminescence dates obtained for quartz and feldspar grains, climatostrati graphic interpretations of oxygen isotope curves, con tents of ice rafted material, and Fe and Mn minerals in sediments. In this model, older foraminifers and diatoms are considered as being reworked and inter vals with reversed magnetization of sediments are cor related with episodes of the Brunhes, not Matuyama, epoch. Detailed analysis of sediment cores obtained recently throughout the entire Arctic Ocean has stim ulated most researchers to accept the “younger” model.

Assessment of the long-term safety of radioactive waste disposal: 1. Paleoreconstruction of groundwater formation conditions

Isotopic characteristics (δ2H, δ18O, 234U/238U, Ar, 3H) of natural and technogenically affected waters were determined in the area around the burying grounds of the Siberian Chemical Combine with the aim to assess the circulation conditions of natural waters and the safety of radioactive waste disposal in reservoir beds.

The first uranium-thorium dating of the Middle Neopleistocene peat in West Siberia

For a sample from the roof of peat (0–2 cm) located in a reference section for the Middle Neopleistocene in West Siberia near the village of Krivosheino, we obtained an exorbitant value of 14C date ≥53.9 ka B.P. (LU-6024). In the peat proper, the 230Th/U dates obtained by the isochronous method are 195.2 ± 10.8/9.1 ka B.P. for the L/L model and 204.1 ± 17/13 ka B.P. for the TSD model. The palynospectra of the peat characterize, from the bottom up, birch forests with fir and spruce participation; then spruce forests with fir; next spruce-cedar forests, similar to the middle taiga subzone. In the clay, the following palynospectra have been examined: forb-gramineous grasslands and light forests with spruce and Betula fruticosa. In the upper part of clays, the palynospectra reflect the evolution of swampy, birch, light forests with spruce participation. The conclusion is made that the studied part of the section formed at the end of the Samarovo Ice Age and in the last third of the Taz Ice Age. The break in sedimentation related to the erosion contact covers a part of the Samarovo Ice Age and the first two-thirds of the Taz Ice Age.

The First Find of Buried Low-Temperature Hydrothermal Deposits in the Mid-Atlantic Ridge Rift Valley

Buried ferromanganese deposits (FMD) were recovered in the course of vibrodrilling at Station 1361 within the terrace on the western slope of the Mid-Atlantic Ridge (MAR) rift valley at 13 ° N during Cruise 24 of the R/V Professor Logachev in 2004. In the same region, at dredging stations 913, 1057, 1058, 1066, 1083, 1311, and 1362, FMD samples were taken from the surface of metabasites (Fig. 1). Discussed in this work are distinguishing features of the structure and chemical and mineral compositions of these deposits, which allowed us to consider in a new fashion the genesis of some low-temperature hydrothermal systems in the MAR rift valley.

Plutonium in Lake Sediments of the Taimyr Peninsula

A radiochemical study is made of five cores of lake sediments collected from the Taimyr Peninsula. For the first time quantitative data are reported on the content and vertical distribution of 239,240Pu and 238Pu in lake sediments of this region. The plutonium content was found to range from 0.89 Bq/kg in the surface layers to 0.02 Bq/kg in the lower horizons (5-10 cm) of the sediment cores studied. The observed variations in the Pu vertical distribution are interpreted in terms of bioturbation and specific features of water catchment for the lakes studied. The 239,240Pu and 238Pu contents and the 238Pu/239,240Pu activity ratios obtained in this work (0.02-0.10) correspond to the global level for the North hemisphere, although the region studied is not far from the principal nuclear weapons test site of the former Soviet Union in the Novaya Zemlya Archipelago.

230Th/U Chronology and Geochemistry of Irinovskoe Hydrothermal Field (Mid-Atlantic Ridge)

The results of 230Th/U dating and mineralogical–geochemical studies of sulfide ores from the Irinovskoe hydrothermal field and the Severo-Zapadnoe ore occurrence (Mid-Atlantic Ridge) are presented. Sulfides are represented primarily by copper–sulfide ores with 12–30% Cu content; sulfur- and zinc-sulfide ores are distributed less frequently. The analysis of a change in the composition of sulfides over time has made it possible to identify three stages of formation. Each stage assumes that mineral associations are changed from high-temperature (sulfur and copper sulfide) to medium temperature (Zn–Cu and Zn-sulfide) sulfide ores. The whole age range of formation of the hydrothermal deposits falls within the time interval of about 58000–8000 for the Irinovskoe field and 69000–11000 years ago for the Severo-Zapadnoe ore occurrence.

U–Th age of the Kazantsevo (MIS 5) Horizon of the Upper Neopleistocene Ust Oda reference section, Baikal Region

For the first time, the organic sediments of the Kazantsevo Horizon (Baikal Region) were characterized geochronometrically. The 230Th/U age of the buried gyttias from the Upper Neopleistocene Ust Oda stratotypical section on the Kitoi River was determined using a new version of isochronous approximation. The assemblage of all the 230Th/U age data, which were obtained taking into account the errors in the entire range from 136 to 86 kyr, indicates that most likely gyttia age is 115–104 kyr (MIS 5d). Thus, the paleontological conclusions on the Kazantsevo age of the Ust Oda Formation with buried gyttias are confirmed. Our geochronometric data supplement and make more reliable the age model of the formation of sedimentary rocks of the Ust Oda section.

Chronostratigraphy of the Cheremoshnik key section (Yaroslavl Volga region) based on new geochronological, palynological, and paleosol data

According to radiochemical and biostratigraphic studies of the buried peat layer in the Cheremoshnik key section on the East European plain, the first age dating of this peat was obtained and its assignment to the Mikulino interglacial was confirmed. The Th/U isotope age data obtained for the peat horizon allow us to state with confidence that it was formed during the MIS5e. It was found that a variety of signs, including the lithological characteristics of dated layers and climatic indexes, is evidence that the Cheremoshnik site and Borisoglebsk upland occurred in the periglacial zone during MIS3–MIS2.