Biohydrochemistry of marine environment and transformations of biogenic substances and oil hydrocarbons on the southeastern Sakhalin shelf

Mathematical simulation is used to study the biotransformation conditions of compounds of organogenic elements (C, N, P, Si) and oil hydrocarbons in the water of southeastern Sakhalin shelf. The input data for calculations were evaluated with the use of Sakhalin Shelf GIS or taken from the reference literature and materials of expedition studies. The values of water discharges through the boundaries of the zones chosen within the shelf water area and through the interface with the Sea of Okhotsk were derived from the characteristics of currents estimated by means of Bergen University oceanic model based on normal long-term monthly thermohaline parameters obtained from the Sakhalin Shelf GIS. The intraannual variations of the concentrations of organic and mineral compounds of C, N, P, and Si, as well as oil hydrocarbons because of biotransformation of substances by organisms of the community (bacteria, phytoand zooplankton) were evaluated in calculations with CNPSi-model. The results of calculations, revealing the features of the dynamics of substances, the biomass of organisms, and their activity in matter biotransformations were analyzed.     

On water circulation in Tatar Strait

Numerical modeling with the help of an oceanic model developed in the Bergen University and with mean annual data was used to carry out monthly calculations of water circulation fields in Tatar Strait, to calculate the vertical velocities and horizontal transfer rates between three areas identified within the strait and on its external boundaries. Analysis of calculation results revealed new features in water circulation in the strait (in particular, in winter) and made it possible, for the first time, to jointly evaluate water exchange components on the external boundaries and within the strait.     

Nature of electric conductive layers of the upper crust and infrastructure of granites of the Central Tien Shan

We studied the infrastructure of granite massifs of the Central Tien Shan and its correlation with the electric conductive layer of the upper crust, which made possible to reveal new peculiarities of the structure of the granite layer in the region and to clarify the nature of low resistivity layers.     

Large-volume silicic volcanism in Kamchatka: Ar–Ar and U–Pb ages,isotopic, and geochemical characteristics of major pre-Holocene caldera-forming eruptions

The Kamchatka Peninsula in far eastern Russia represents the most volcanically active arc in the world in terms of magma production and the number of explosive eruptions. We investigate large-scale silicic volcanism in the past several million years and present new geochronologic results from major ignimbrite sheets exposed in Kamchatka. These ignimbrites are found in the vicinity of morphologically-preserved rims of partially eroded source calderas with diameters from ～ 2 to ～ 30 km and with estimated volumes of eruptions ranging from 10 to several hundred cubic kilometers of magma. We also identify and date two of the largest ignimbrites: Golygin Ignimbrite in southern Kamchatka (0.45 Ma), and Karymshina River Ignimbrites (1.78 Ma) in south-central Kamchatka. We present whole-rock geochemical analyses that can be used to correlate ignimbrites laterally. These large-volume ignimbrites sample a significant proportion of remelted Kamchatkan crust as constrained by the oxygen isotopes. Oxygen isotope analyses of minerals and matrix span a 3‰ range with a significant proportion of moderately low-δ¹⁸O values. This suggests that the source for these ignimbrites involved a hydrothermally-altered shallow crust, while participation of the Cretaceous siliceous basement is also evidenced by moderately elevated δ¹⁸O and Sr isotopes and xenocryst contamination in two volcanoes. The majority of dates obtained for caldera-forming eruptions coincide with glacial stages in accordance with the sediment record in the NW Pacific, suggesting an increase in explosive volcanic activity since the onset of the last glaciation 2.6 Ma. Rapid changes in ice volume during glacial times and the resulting fluctuation of glacial loading/unloading could have caused volatile saturation in shallow magma chambers and, in combination with availability of low-δ¹⁸O glacial meltwaters, increased the proportion of explosive vs effusive eruptions. The presented results provide new constraints on Pliocene–Pleistocene volcanic activity in Kamchatka, and thus constrain an important component of the Pacific Ring of Fire.     

Within-plate zones of concentrated deformation: Tectonic structure and evolution

A specific category of extremely complex linear within-plate structural zones is described. The state of their art, structure and evolution, abundance in various regions, and geodynamic settings are discussed, and formation models are considered.     

Polygenic nature of granite clastites: Communication 2. Secondary and supergene reworking of granitic clastites

Clastogenic rocks spatially associated with granite massifs have been reported in the geological literature from different regions: Caucasus (Leonov, 1974, 1991), Urals (Puchkov, 1968), Kazakhstan (Svarichevskaya and Skublova, 1973), Transbaikal region (Leonov, 2008; Lobanov et al., 1991), Tien Shan (Leonov et al., 2008), North America (Beroush, 1991; Lukin, 1989, 2007; Pippin, 1973). In some places, they represent crushed rocks of indigenous massifs. In other places, they make up accumulations and aprons of clastic products of the granitic composition both on the surface and beneath the sedimentary cover. In the first communication (Leonov et al., 2014) devoted to the origin of granite clastites, we examined specific features of the structure and evolution of granite bodies at the posthumous development stage, i.e., after cooling and introduction into the consolidated layer of the Earth’s crust. It was shown that such rocks are formed at least due to two main processes: supergene1 (chemical and physical weathering) and tectonic (prototectonics and posthumous disintegration). Although the rocks are highly similar in composition, structure, and bedding conditions, they are marked by several specific features described in the first communication that provide insight into their genetic nature. However, the problem of morphostructural characteristics and genetic interpretation of granite clastites cannot be closed here. Reconstruction of the “primary” origin of clastic granitic bodies in some, far from single, cases is complicated by the following fact: the exhumed massifs of tectonically disintegrated granitoids undergo supergene transformations, while sediments in the weathering crust are involved in tectonic reworking. Thus, clastites can be formed in several stages with different successions of events: supergene processes (formation of the weathering crust) can precede the tectonic reworking of rocks or succeed the formation of tectonomixtites. Determination of diagnostic properties of genetically different clastic rocks and stages of their lithostructural alteration is important for solving the issues of regional geology, development of methods for the study of genetically complex sequences, as well as paleogeographic and paleotectonic reconstructions. This problem acquires a specific importance because of two circumstances: first, its solution is at the intersection of two geological disciplines (lithology and tectonics); second, granitic clastite bodies often represent commercial hydrocarbon reservoirs (Areshev et al., 1997; Gavrilov, 2000; Izotov et al., 2003; Lobanov et al., 1991; Lobusev et al., 2002; Lukin, 2007; Martynova, 2002; Pippin, 1973; Sitdikova and Izotov, 2002). Let us discuss two scenarios of the succession of events: scenario 1—“tectonic mixtite” → “supergene reworking”; scenario 2—“weathering crust” → “tectonic reworking”. All other versions are combinations of these two types.     

The use of a spatially heterogeneous simulation model for studying biotransformation processes of nitrogen and phosphorus compounds and the dynamics of oxygen dissolved in water in the ecosystem of Neva Bay, the Gulf of Finland: 2. Input data for calculations, modeling results, and their analysis

The data collected for model calculations is systematized for natural and design conditions. The natural conditions did not take into account the effect of the complex of water-protection structures on the hydrological regime of Neva Bay and on the biogenic load onto this water area, while the design conditions, conversely, reflected the possible impact of those structures on the hydrology and ecology of the area. Numerical experiments were used to study the processes of transformation of N and P compounds and the dynamics of dissolved O₂ in Neva Bay water area. In the comparison of the calculated and observed concentrations of biogenic substances, Theil criterion was evaluated to assess the adequacy of the model in reproducing the concentration fields of the distribution of biogenic substances over Neva Bay water area. The major qualitative and quantitative features of the formation of the spatial heterogeneity and the time variations in the concentrations of biogenic element compounds over Neva Bay water area are identified. Possible improvements of the model in the reproduction of the complex of processes that are of particular importance for the development of substance transformations in shallow ecosystems are considered.     

Modeling of the marine environmental pollution by petroleum hydrocarbons and their biotransformation in Tatar Strait waters

A hydroecological model is used for simultaneous studying water pollution processes by petroleum hydrocarbons and their decay under the oceanographic conditions of Tatar Strait. The model calculations were based on long-term averaged observational data on interannual variations of water temperature, light intensity, and transparency. Some oceanographic characteristics of the strait were reconstructed with the help of GIS “Sakhalin Shelf.” The strait’s water area was divided into three regions, and water exchange between them and the neighboring regions of the Sea of Japan was estimated by a hydrodynamic model. The results of the study made it possible to assess interannual variations in the concentrations and inner fluxes of petroleum hydrocarbons, oil-oxidizing bacteria biomasses, and the characteristics of their oxidation activity.