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1.
The results of study of the isotopic-lithological compositions of carbonate and terrigenous-carbonate rocks in the Soyana
River section (northern East European Platform, Arkhangel’sk district) are presented. The results make it possible to identify
10 main lithotypes and show a wide variation range of δ13C (from −2.2 to +3.6‰, PDB) and δ18O (from 22.5 to 30.5‰, SMOW). These lithological features and isotopic compositions suggest that the rocks were formed in
a shallow-marine setting characterized by rapidly changing sedimentation conditions in various facies (and/or paleoecological)
zones: inlets, lagoons, supralittoral, littoral, and shoals. Periods of aridization and humidization are recorded. The results
also indicate numerous synsedimentary short-term hiatuses and stages of increased continental runoff—episodic pulsatory input
of clastic material with the continental paleoflows. 相似文献
2.
Kuleshov Yuriy Gregory Paul Watkins Andrew B. Fawcett Robert J. B. 《Natural Hazards》2020,104(2):1295-1313
Tropical cyclones (TCs) affect countries in the Southern Hemisphere (SH) tropics every year causing significant humanitarian impacts and much damage to the natural environment. To reduce TC impacts on societies, early warning systems (EWS) are used to communicate the risk to the public. In 1999, the Climate Change and Southern Hemisphere Tropical Cyclones International Initiative (CCSHTCII) was established to enhance EWS for TCs in SH countries, with particular focus on support for small island developing states and least developed countries to provide effective public early warnings of TC risk. In this paper, recent activities of the CCSHTCII to strengthen TC EWS are presented. Using TC best track data from the SH TC historical data archive, the impact of the El Niño–Southern Oscillation (ENSO) on inter-annual and spatial variability of TC activity is examined. TC-ENSO relationships in the SH are analysed and used as a scientific basis for the production of TC season outlooks. Communication of TC early warnings through TC season outlooks is described, and recommendations for improving outlooks are provided.
相似文献3.
The Parnok deposit is made up of stratiform lodes of iron (magnetite) and manganese (oxide-carbonate, carbonate, and carbonate-silicate) ores localized among terrigenous-carbonate sediments (black shales) on the western slope of the Polar Urals. The lithological study showed that ore-bearing sediments were accumulated in a calm hydrodynamic setting within a relatively closed seafloor area (trap depressions). Periodic development of anaerobic conditions in the near-bottom seawater was favorable for the accumulation of dispersed organic matter in the terrigenous-carbonate sediments. Carbon required to form calcium carbonates in the ore-bearing sediments was derived from carbon dioxide dissolved in seawater. In the organic-rich sediments, carbonates were formed with the participation of carbon dioxide released by the destruction of organic matter. However, δ13C values (from 0.5 to ?4.4‰ PDB) suggest a relatively low fraction of the isotopically light biogenic carbon in the host calcite. The most probable sources of Fe and Mn were hydrothermal seepages at the seafloor. The Eh-pH conditions during stagnation were favorable for the precipitation of Fe and accumulation of Mn in a dissolved state. Transition from the stagnation regime to the concentration of oxygen in near-bottom waters was accompanied by oxidation of the dissolved Mn and its precipitation. Thus, fluctuations in Eh-pH parameters of water led to the differentiation of Fe and Mn. Initially, these elements were likely precipitated as oxides and hydroxides. During the subsequent lithification, Fe and Mn were reduced to form magnetite and rhodochrosite. The texture and structure of rhodochrosite aggregates indicate that manganese carbonates already began to form at the diagenetic stage and were recrystallized during the subsequent lithogenetic stages. Isotope data (δ13C from ?8.9 to ?17.1‰ PDB) definitely indicate that the oxidized organic matter of sediment served as the main source of carbon dioxide required to form manganese carbonates. Carbonates from host rocks and manganese ores have principally different carbon isotopic compositions. Unlike carbonates of host rocks, manganese carbonates were formed with an active participation of biogeochemical processes. Further processes of metagenesis (T ≈ 250–300°C, P ≈ 2 kbar) resulted in the transformation of textures, structures, and mineral composition of all rocks of the deposit. In particular, increase in temperature and pressure provided the formation of numerous silicates in manganese ores. 相似文献
4.
A. M. Devyatkin D. A. Denisenkov V. Yu. Zhukov Yu. V. Kuleshov S. V. Chernyshev G. G. Shchukin 《Russian Meteorology and Hydrology》2018,43(1):56-61
The potential of Doppler weather radars in estimating the speed and direction of airflows within the area of coverage is investigated. It is demonstrated that the usage of one radar does notre-trieve the field of these parame ters but makes possible the solution of partial problems. Different ways of solution are considered. The method based on multiposition radiolocation is proposed as the most promising one. 相似文献
5.
V. I. Vinogradov G. A. Belenitskaya M. I. Bujakaite V. N. Kuleshov M. A. Minaeva B. G. Pokrovskii 《Lithology and Mineral Resources》2006,41(3):271-279
In previous communications based on the study of sulfur and strontium, we showed that Lower Cambrian rocks of the Irkutsk Amphitheater underwent a significant epigenetic transformation. All postsedimentary alterations of rocks are related to the influence of water solutions that provoke the direct (physical) dissolution of material and its chemical transformation. In particular, an appreciable portion of anhydrites disappeared from the section due to reduction. Probably, these processes took place several times in the past and they are continuing at present. A similar conclusion was deduced from the strontium isotopic composition of carbonate rocks. Their strontium isotopic composition is usually shifted relative to the primary composition, although the prevalence of sulfate and carbonate rocks in the section promotes the stability of strontium isotopic composition with respect to secondary alterations. The carbon isotope system is even more stable due to the abundance of carbonate rocks in the section. This circumstance is probably responsible for the incapacity of isotope data to serve as obvious evidence of the epigenetic transformation of carbonates. The major elements of the evolution of carbon isotope signature could be retained since the sedimentation stage. 相似文献
6.
Summary Convective Available Potential Energy (CAPE) is the driving force for thunderstorm development. CAPE is closely controlled
by wet bulb temperature. The lightning activity measured by a network of ten lightning flash counters widely distributed across
continental Australia was studied as a function of wet bulb temperature. At each of the stations, the monthly total of lightning
ground flashes, N, increased sharply with the increase of the monthly mean daily maximum wet bulb temperature, Tw, max. The dependence was strongest in the tropics and became less pronounced at temperate latitudes. In Darwin (latitude 12° S),
the lightning ground flash activity increased by over three orders of magnitude over a 7 °C range of Tw, max. The corresponding increases for Coffs Harbour (latitude 30° S) and for Melbourne (latitude 38° S) were about one and a half
orders of magnitude and about half an order of magnitude, respectively, each over a 10 °C range of Tw, max. Power law approximations were derived for each of the ten stations and showed that the logarithm of N was directly proportional
to the power, P, of Tw, max. The value of P showed a sharp exponential decrease with increasing latitude away from the equator. 相似文献
7.
V. I. Vinogradov G. A. Belenitskaya M. I. Bujakaite V. N. Kuleshov M. A. Minaeva B. G. Pokrovskii 《Lithology and Mineral Resources》2006,41(1):85-97
New isotope data on Lower Cambrian rocks of the Irkutsk amphitheater are reported in three communications. The first communication
is devoted to the sulfur isotopic composition, which is most sensitive to ostsedimentary geochemical transformations of sulfate
rocks in saliferous formations. It is shown that δ34S values in Bel’sk and Zhigalovo boreholes are within 22–35‰ The lowest values are close to the sulfur isotopic composition
of a halogenic basin, while the highest values are related to epigenetic sulfate reduction. This process was responsible for
the elimination of 100 m of anhydrites from the Lower Cambrian section. 相似文献
8.
The results of investigation of the Bikkulovskoe manganese deposit confined to volcanosedimentary piles of the Magnitogorsk
paleovolcanic belt are presented. The paper characterizes the geological setting of the deposit and mineral-chemical compositions
of ores and enclosing rocks (volcanomictic sandstones; ferruginous, manganiferous, and ferruginous-siliceous tuffites; and
jasperites). Analysis of the data obtained made it possible to identify four sequential stages of deposit formation: (1) accumulation
and diagenesis of ore-bearing sequences (D2–3); (2) burial and low-grade (T = 200–250°C, P = 2 to 3 kbar) regional metamorphism of rocks (D2–3-C1); (3) tectonic deformations of volcanosedimentary piles (C2-P); and (4) hypergenesis and partial denudation of rocks (MZ-CZ). According to the model proposed for the accumulation of
ore-bearing rocks, the productive member was formed in a zone of hydrothermal solution outflow to the seafloor surface. Discharge
of solutions and precipitation of Fe and Si began below the seafloor surface (rather than above the surface) in the near-bottom
sequence of volcanomictic sediments. Upon reaching the seafloor, the impoverished solutions mixed with seawater and gave up
metals completely: Fe and Mn were transferred to sediments to make up the ore-bearing bed. Thus, zonal sediments with ferruginous
tuffites at the base and manganese ores at the top were formed. 相似文献
9.
Brusnitsyn A. I. Starikova E. V. Ignatova M. V. Kuleshov V. N. 《Lithology and Mineral Resources》2019,54(2):159-185
Lithology and Mineral Resources - The paper presents the results of study of metalliferous (ferromanganese and manganese) rocks at the Nadeiyakha ore occurrence (Pai-Khoi) discovered in 2010. The... 相似文献
10.