Precambrian glaciations and associated biospheric events

Precambrian glaciations are established to have occured during several brief periods in the Late Archean, Early Proterozoic, Late Riphean, and Vendian. These extreme climatic events of the Late Archean and post-Archean Earth history were accompanied by significant changes in the biosphere and biota. The terminal stages of Precambrian glaciations were marked by intense development of some existing groups, and the appearance of new groups of organisms. This may be explained by associated radical transformations of environments in all the biosphere subsystems, which resulted in substantial ecosystem and related biotic crises. The crises released former and yielded new ecological niches, on the one hand, and provoked enhanced mutations in organisms and rapid appearance of new forms, on the other. The most viable new forms as well as some of taxa that survived the crisis colonized released and newly formed niches to become more diverse and dominant groups. Thus, activation of abiotic and subsequent biotic factors during and after glaciations stimulated the renewal of the biota and acceleration of the evolutionary process.     

Geological structure of the Curonian Spit (of the Baltic Sea) and its evolution history (revised)

The origin and evolution history of the Curonian Spit in the Baltic Sea are discussed based on geological and geomorphologic data. Evidence of the correlation between the spit formation stages and the Holocene sea level oscillations is presented. The ledges of moraine basement and marine accumulative features formed a single barrier. Its subsequent transformation occurred under the influence of the wave-related lithodynamic and eolian processes.     

青海地区地震序列参数的早期特征研究

采用时间序列的"传染型余震序列"(ETAS)模型系统估算了青海地区地震序列参数,并对地震序列的震后早期特征进行分析。采用"自然边界法"选取了2009年以来青海地区9个地震序列,利用"震级-序号"法确定了每个地震序列的完整性震级M_c,并对每个地震序列进行估算。研究表明,截止震级选取对地震序列参数的影响很大,在应用中需谨慎。α值和p值的稳定时间与序列的主震震级间没有明显的关系,主震震级较大的地震序列,序列参数的稳定时间可能较短;主震震级较小的地震序列,序列参数的稳定时间也可能较长。同一个地震序列,α值和p值的稳定时间与不同截止震级间也没有明显的对应关系。最后给出了研究区域地震序列参数的最长稳定时间和最短稳定时间。     

Late Vendian postcollisional leucogranites of Yenisei Ridge

The Late Vendian (540–550 Ma) U–Pb zircon age of postcollisional granitoids in the Osinovka Massif was obtained for the first time. The Osinovka Massif is located in rocks of the island-arc complex of the Isakovka Terrane, in the northwestern part of the Sayany–Yenisei accretion belt. These events stand for the final stage of the Neoproterozoic history of the Yenisei Ridge, related to the completing accretion of the oceanic crust fragments and the beginning of the Caledonian orogenesis. The petrogeochemical composition and the Sm–Nd isotopic characteristics support the fact that the granitoid melt originated from a highly differentiated continental crust of the southwestern margin of the Siberian Craton. Hence, the granite-bearing Late Riphean island-arc complexes were thrust over the craton margin at a distance considerably exceeding the dimensions of the Osinovka Massif.     

Heavy load and high potential: anthropogenic pressures and their impacts on the water quality along a lowland river (Western Bug,Ukraine)

A pronounced pollution of surface water bodies in the Western Bug River Basin, Ukraine, has been caused by outdated or overloaded wastewater treatment plants, agriculture, industry and coal mining. These pressures have led to a generally poor state of both chemical and microbiological variables creating health risks of various kinds. The state of surface water quality for the Western Bug and five main tributaries was assessed by measuring physical, chemical and microbiological indicators during field campaigns in autumn 2009 and spring 2010. Longitudinal profiles were sampled to identify major sources of pollution and to reveal dominant processes of matter turnover. In addition, the occurrence of antibiotic resistant strains in isolates from stations along the Bug River was investigated. Results clearly underpin the negative impact of the Poltva River as a major source of pollution for the Bug River and further outline an elevated potential health risk from pathogenic bacteria originating from this source. Despite these devastating impacts, a high elimination potential of the Bug River with respect to primary organic loads as well as elimination of pathogenic bacteria was observed particularly at Dobrotvir Reservoir. Further downstream, pollution is kept high because of untreated waste effluents and phytoplankton mass developments due to high phosphorus concentrations.     

The dynamics of deep magmas

This study attempts to substantiate a model of magma ascent from deep-seated sources driven by the density difference between magmas and wall rocks in a plastic solid medium via hydraulic fracturing (magma-driven fracturing). The difference between magma and wall rock densities causes overpressure development in the head of a magma column. With increasing height of the column or decreasing magma density, the overpressure can build significantly, which is valid for the case of continuous magma conduit from a deepseated source. The depth of mantle chambers, their vertical extent, and magma densities seem to be the key factors in the formation of volcanoes and intracrustal intrusions. Intermittent (or peripheral) magma chambers under volcanoes and crustal-mantle intrusive bodies may be formed at strength barriers, in the zone of elastoplastic transition and at the mantle-crust boundary.     

Structural position of large gold ore districts in the Central Aldan (Yakutia) and Argun (Transbaikalia) superterranes

Gold ore districts in the Siberian (North Asian) craton and bordering terranes have been studied. Studies showed the long duration of gold concentration processes (Early Cambrian to Late Mesozoic and Cenozoic) and the influence of structural geological, magmatic, and metallogenic factors on the formation of ore districts. The largest Late Mesozoic (J–K) accumulations of gold deposits in southeastern Russia were discovered in the Aldan–Stanovoi Shield and at the northern margin of the Argun superterrane in the Aldan (Yakutia), Balei (Transbaikalia), and Gonzha (Upper Amur area) ore–placer districts.The geological and geophysical positions of these three districts have been compared. All of them are situated in zones of influence of variously trending long-lived deep faults, bordered by large Precambrian uplifts, and spatially (paragenetically) related to local magma chamber domes of Late Mesozoic (J–K) intrusive, subvolcanic, and extrusive–effusive bodies, dikes, and terrigenous pyroclastic blankets. The areas of Jurassic–Cretaceous volcanoplutonic rocks are related to the influence of the East Asian sublithospheric “superplume.”All this confirms the important ore-controlling role of large long-lived deep faults (in the form of global and regional gravity gradient zones) in the distribution of highly productive precious-metal ore–magmatic systems. This suggests that the junctions between gravity gradient zones of different trends and ranks are important to the identification of gold prospects in metallogenic prediction studies and small-scale prospecting. The Archean–Proterozoic age and the great occurrence depth of the tectonic zones suggest that extensive long-lived mobile zones (before the post-Cambrian breakup of the Siberian craton) significantly affected further evolution of the orogenic belts bordering the craton and their metallogeny, including the distribution of precious- metal deposits.     

Yegorovite,Na<Subscript>4</Subscript>[Si<Subscript>4</Subscript>O<Subscript>8</Subscript>(OH)<Subscript>4</Subscript>]·7H<Subscript>2</Subscript>O,a new mineral from the Lovozero alkaline pluton,Kola Peninsula

A new mineral, yegorovite, has been identified in the late hydrothermal, low-temperature assemblage of the Palitra hyperalkaline pegmatite at Mt. Kedykverpakhk, Lovozero alkaline pluton, Kola Peninsula, Russia. The mineral is intimately associated with revdite and megacyclite, earlier natrosilite, microcline, and villiaumite. Yegorovite occurs as coarse, usually split prismatic (up to 0.05 × 0.15 × 1 mm) or lamellar (up to 0.05 × 0.7 × 0.8 mm) crystals. Polysynthetic twins and parallel intergrowths are typical. Mineral individuals are combined in bunches or chaotic groups (up to 2 mm); radial-lamellar clusters are less frequent. Yegorovite is colorless, transparent with vitreous luster. Cleavage is perfect parallel to (010) and (001). Fracture is splintery; crystals are readily split into acicular fragments. The Mohs hardness is ～2. Density is 1.90(2) g/cm³ (meas) and 1.92 g/cm³ (calc). Yegorovite is biaxial (?), with α = 1.474(2), β = 1.479(2), and γ = 1.482(2), 2V _meas > 70°, 2V _calc = 75°. The optical orientation is X ∧ a ～ 15°, Y = c, Z = b. The IR spectrum is given. The chemical composition determined using an electron microprobe (H₂O determined from total deficiency) is (wt %): 23.28 Na₂O, 45.45 SiO₂, 31.27 H₂O_calc; the total is 100.00. The empirical formula is Na_3.98Si_4.01O_8.02(OH)_3.98 · 7.205H₂O. The idealized formula is Na₄[Si₄O₈(OH)₄] · 7H₂O. Yegorovite is monoclinic, space group P2₁/c. The unit-cell dimensions are a = 9.874, b= 12.398, c = 14.897 Å, β = 104.68°, V = 1764.3 ų, Z = 4. The strongest reflections in the X-ray powder pattern (d, Å (I, %)([hkl]) are 7.21(70)[002], 6.21(72)[012, 020], 4.696(44)[022], 4.003(49)[211], 3.734(46)[(bar 2) 13], 3.116(100)[024, 040], 2.463(38)[(bar 4)02, (bar 2)43]. The crystal structure was studied by single-crystal method, R _hkl = 0.0745. Yegorovite is a representative of a new structural type. Its structure consists of single chains of Si tetrahedrons [Si₄O₈(OH)₄]∞ and sixfold polyhedrons of two types: [NaO(OH)₂(H₂O)₃] and [NaO(OH)(H₂O)₄] centered by Na. The mineral was named in memory of Yu. K. Yegorov-Tismenko (1938–2007), outstanding Russian crystallographer and crystallochemist. The type material of yegorovite has been deposited at the Fersman Mineralogical Museum of Russian Academy of Sciences, Moscow.