Vol 477, No 1 (2017)

The U–Pb age of the boundary between the Lower and Middle Carboniferous has been determined on zircons separated from a volcanic tuff layer within a limestone unit near the roof of the Serpukhovian Stage in an occurrence at the right bank of the Iset’ River. The zircons have been dated using SIMS SHRIMP-II at 320 ± 3 Ma. The result agrees well with the accepted age of the boundary between the Serpukhovian and Bashkirian ages (323.2 ± 0.4 Ma, [1]).

The granitic magmatism occurred at the precollisional stage of the continentalization of the mafic basement of the Shchuch’ya island arc system. The first U–Pb (SIMS, SHRIMP II) data on zircons indicate three pulses of transformation of the oceanic crust into a continental crust: in the Silurian and Middle and Late Devonian. The age of the Yanganape granite is 429 ± 4 Ma, which corresponds to the Late Wenlockian; that of the Yurmeneku massif is 385 ± 2 Ma (Givetian); and that of the Canyon Massif is 368 ± 3 Ma (Famennian). The zircons from the Yanganape granite yielded an age of 335 ± 4 Ma, which corresponds to the Early Carboniferous (Visean). Similar ages were noted in uranium-rich zircons from the Canyon Massif granite. They correlate with the collision time of the island arc with the eastern edge of the Eastern European paleocontinent, and it is possible that this event caused disturbance of the U–Pb system of zircons in the islandarc granites of the Shchuch’ya zone.

The Rb–Sr and ¹⁴⁷Sm–¹⁴³Nd age data obtained for sheeted dolerite dykes and rocks of the Platinum Belt of the Urals within the Tagil segment of the paleoceanic spreading structure (Middle Urals) are discussed. The study of the Rb–Sr isotope systematics of gabbro allowed us to reveal errochronous dependencies, which yielded ages of 415 and 345 Ma at (⁸⁷Sr/⁸⁶Sr)₀ = 0.70385 ± 0.00068 and 0.7029 ± 0.0010, correspondingly. The ¹⁴⁷Sm–¹⁴³Nd isotope age data demonstrate a specific coincidence of the chronometric ages of the sheeted dolerite dyke complex (426 ± 54, 426 ± 34, and 424 ± 19 Ma) and gabbro from the Revda gabbro–ultramafic massif (431 ± 27 Ma) and from screens between dolerite dykes in the sheeted dyke complex (427 ± 32 Ma, 429 ± 26 Ma). The proximity of the ¹⁴⁷Sm–¹⁴³Nd ages of gabbro and dolerite can be explained by the thermal effect of the basaltic melt, which is the protolith for the dyke complex, on the hosting gabbro.

The age distribution of detrital zircons from Upper Riphean and Early Carboniferous sandstones of the northwest part of Nordenskiöld Land (Spitsbergen Island) was studied. The results obtained supplement the previously known data on the rocks of Precambrian and Paleozoic masses of West Spitsbergen. Integrated consideration of these data showed that the time interval from the Middle Riphean to the Early Carboniferous inclusive might be subdivided into at least five stages characterized by quite different provinces supplying detritus to sedimentary basins. (The relics of these latter are represented in the present structure of western Svalbard.) The most ancient distinguished event of alteration of the sources of sedimentary matter (at the boundary of the Middle and Late Riphean) corresponds to the consolidation time of the ancient basement of Svalbard.

Before our studies, it was considered that the Bagrusha rhyolite–porphyry complex (BC) including veins and thin dykes occurring in the Kusa region among deposits presumably of the Satka and Avzyan Formations of the Lower and Middle Riphean, respectively. Based on the U–Pb SHRIMP and IDTIMS studies of zircons from rhyodacite—porphyry, we established the age of the BC formation of T₀ = 1348.6 ± 3.2 Ma for the first time. The age obtained is inconsistent with the idea on the Paleozoic age of the BC and the geological situation shown on geological maps of the region. The age (T₀ = 1348.6 ± 3.2 Ma) of rhyodacite–porphyry from the BC provides evidence for acid volcanism controlled by the Mashak (Middle Riphean) magmatic event in the region, and deposits hosting volcanic rocks of the BC cannot be younger than the base of the Middle Riphean, i.e., the Mashak Formation, which was not previously distinguished by researchers in the western part of the Kusa and Bakal–Satka regions. At the same time, it is possible that deposits hosting dykes and veins of the granite–rhyolite formation may have a Bakal (Lower Riphean) age.

For the first time, biogenic nanomagnetite has been detected in banded iron formation of the Lebedinskii deposit of the KMA and has been demonstrated to be a primary mineral. This finding may imply a key role of metabolic processes in primary deposition of divalent iron with formation of trivalent iron minerals, the precursors of banded iron formation of the KMA.

The first results are presented for U-Pb SHRIMP-II dating of zircons from the upper part of the Khivachian regional horizon (stage) of the Regional Stratigraphic Scale (RSS) of the Permian in northeastern Russia. The obtained isotope age of 255 ± 2 Ma is close to that of the present boundary between the Wuchiapingian and Changhsingian stages of the Permian system in the International Stratigraphic Scale (254.1 Ma). Based on the distribution of bivalves—Intomodesma spp. and Claraioides aff. primitivus (Yin)—in the sections considered, their relations to the stratigraphic positions of the samples considered and dated formerly, and in view of the interregional correlation of recent δ¹³С_org data for clayey rocks, one may assume with certainty that most of the regional zone of Intomodesma costatum corresponds to the upper part of the Wuchiapingian stage. Here, the Changhsingian stage in northeastern Asia complies only with the uppermost part of this zone within the I. postevenicum subzone and, partially, of Otoceras layers within the Otoceras concavum zone.

The age data (U–Pb, SHRIMP II) of zircons from rutile eclogites of the Maksutov Complex (MC) (village Shubino, Southern Urals) were subdivided into three age groups. The Neoproterozoic zircons (561 ± 10 Ma) recorded the formation stage of eclogites, the protolith of which was diabase and gabbro-diabase bodies. The Neoarchean ancient zircons (2884 ± 36 Ma) belong to the mantle substratum, which was repeatedly transformed (2303 ± 12, 2008 ± 18, 1626 ± 59 Ma). Zircons of early Ordovician–early Silurian age (433–477 ± 6 Ma; 340 ± 40 Ma) recorded superimposed processes, corresponding to high-pressure metamorphism.

The reconstructions of landscape dynamics and fire regimes in the southeastern part of Meshchera Lowlands in the Holocene are presented. Based on study of the fire layers in peat deposits of bogs, as well as botanical and palynological analyses of peat and morphological analysis of soils, it was established that the long-period dynamics for landscapes of the territory during the Middle and Late Holocene was determined primarily by shifts in fire regimes. Since 8000 cal. yr. BP, periods with high fire frequency (from 15–20 to 120 years) alternated with intervals when the fire frequency varied from 500–600 to 1800 years. The paleoecological reconstructions showed that increased fire activity was also recorded prior to human settlement in the southeastern part of the Meshchera Lowlands, when the action of the anthropogenic factor was the lowest.

The self-oscillation process of heat redistribution in the system ocean–atmosphere–continent should be considered as one of the mechanisms of multidecade climate variability. Based on the data of monitoring for the period 1960–2014, interdecadal variations in heat capacity in the upper active layer are estimated for the northwestern part of the Pacific Ocean, which is one of the most informative regions of the World Ocean.

Experiments on generation mechanisms of sea water spray under hurricane wind were performed using shadow illumination high-speed video recording from several camera positions. Classification of fragmentation mechanism leading to generation of spray was conducted. Statistics of the events causing generation of spray was studied. A phenomenological model was developed based on the methods of statistical physics to describe the “bag-breakup” generation mechanism. The function of spray generation was conducted on this basis, which describes well the experimental data obtained under hurricane winds in the natural and laboratory conditions.

Influence of the spray generation due to the fragmentation of the “bag-breakup” type on momentum exchange in the atmospheric boundary layer above the sea surface at hurricane winds was investigated on the basis of the analysis of the results of laboratory experiments. It was shown that aerodynamic drag is determined by the contribution of three factors: first, the drag of the “bag-breakup” canopies as obstacles; second, acceleration of the spray formed during fragmentation by the air flow; and the third factor is related to the stratification of the near-water atmospheric layer due to the presence of levitated water droplets. Combination of all three factors leads to a non-monotonous dependence of the aerodynamic drag coefficient on wind speed, which confirms the results of the field and laboratory measurements.