Biogeochemistry of encrusting sponges of the family Lubomirskiidae in Southern Lake Baikal

ICP-MS analyses of encrusting sponges indicate that their predominant chemical elements are, along with Si, by P, Al, Fe, Ca, S, Mg, K, Na, Cu, Mn, Zn, Ti, Ba, and Br. The sponges are most significantly enriched in Al > Cu > Ti > REE > Mn > P relative to their aqueous habitat and in Cu > I > Cd > P > Br > As ≥ S relative to the relatively rudaceous bottom sediments. One of the sources of elements occurring the aqueous habitat and being of vital importance for the activity of the sponges was proved to be the rock substrates.     

Metamict transformations in some niobates and zircons according to X-ray absorption spectra

The niobium and zirconium L _III-absorption spectra in some niobates and zircons were obtained with a vacuum focusing crystal spectrometer. The effective charges of Nb and Zr in these minerals were derived from the X-ray absorption spectra. The fine structure of the absorption spectra and effective charges Nb and Zr in metamict, partly-metamict minerals and crystalline analogues made it possible to draw a conclusion as to the nature of the first coordination sphere of Nb and Zr during metamict decay and subsequent recrystallization under annealing of these minerals.     

Structural evolution of the Main Ural Fault Zone in the western framework of the Voikar-Synya ophiolite massif

Multistage deformations in the Main Ural Fault Zone is recorded in the structural features of this zone in the southern part of the Polar Urals. The deformation of the oldest metamorphic complexes in the Khord??yus massif and Dzelyayu block developed during the precollision stage. After formation of the general nappe-thrust structure of the Urals, these blocks were squeezed to the higher crustal levels. Deformation in other tectonic units started at the early collision stage during regional thrusting. Brittle failure was superposed over the all previously formed structures at the late collision and postcollision stages.     

Interrelation of total precipitation over Eurasia with atmospheric centers of action of the northern hemisphere and with major modes of the North Atlantic surface temperature variability

Conventional average values of Wallace-Gutzler indices for the regional circulations and average values of major variability components of the fields of the North Atlantic surface temperature anomalies are plotted on the geographical map used to analyze the total daily precipitation fields. The computation conditions of average values are defined by the dates classified according to three equiprobable gradations of total precipitation. A projection of conditional average values to the precipitation field points enables to estimate the atmospheric and oceanic “tracks” within the marked out gradations of total precipitation. The stratification and computation of characteristics are carried out for the summer and winter seasons. Large regions are revealed of statistically significant interrelation of the atmospheric circulation and major components of variability of the sea surface temperature anomalies with the extreme gradations of total precipitation for summer and winter seasons. The recommendations are formulated for the use of obtained results in the practice of the seasonal forecasting of meteorological conditions.     

Geologic and biogeochemical role of crustose aquatic lichens in Lake Baikal

Based on materials collected in 2003–2007, data on aquatic lichens of the genus Verrucaria from the rocky littoral zone of Lake Baikal are discussed. The maximum density of their occurrence was observed at a depth of 1.5 m; 95–100% of rock fragments recovered from depths of 1.5–2.2 m are encrusted by 24–43% with the thalli of Verrucaria spp. It was found that the lichens contribute actively to the physical and physicochemical weathering of their rock substrate and prefer to reside on the rocks of granitic composition. The chemical composition of aquatic verrucaria is dominated by the same elements that are most abundant in the rocks (Ca > K > Fe > Al > Mg > P > S > Na > Mn > Sr > Ba), and, in most cases, the characteristic element ratios of the rock compositions are preserved in the composition of the thalli of Verrucaria spp. Compared with the elemental composition of the near-bottom water layer, the lichens most extensively concentrate the elements that slowly migrate in water: Gd > Sm > Pr > Nd > Al > La > Dy > Tb > Y > Lu > Ce > Yb > Be > Tm > Co > Nb > Mn > Zn. Compared with the composition of rocks, the mineral composition of the thalli of Verrucaria spp. is enriched by a factor of 100–10 in Hg > As > P > Zn > Li > S > U > Mo > Se > Cd > Ca > Tl > Sr > Pb > Be.     

Tectonics and geodynamics of Gorny Altai and adjacent structures of the Altai–Sayan folded area

Packages of Late Paleozoic tectonic nappes and associated major NE-trending strike-slip faults are widely developed in the Altai–Sayan folded area. Fragments of early deformational phases are preserved within the Late Paleozoic allochthons and autochthons. Caledonian fold-nappe and strike-slip structures, as well as accompanying metamorphism and granitization in the region, are typical of the EW-trending suture-shear zone separating the composite Kazakhstan–Baikal continent and Siberia. In the Gorny Altai region, the Late Paleozoic nappes envelop the autochthon, which contains a fragment of the Vendian–Cambrian Kuznetsk–Altai island arc with accretionary wedges of the Biya–Katun’ and Kurai zones. The fold-nappe deformations within the latter zones occurred during the Late Cambrian (Salairian) and can thus be considered Salairian orogenic phases. The Salairian fold-nappe structure is stratigraphically overlain by a thick (up to 15 km) well-stratified rock unit of the Anyui–Chuya zone, which is composed of Middle Cambrian–Early Ordovician fore-arc basin rocks unconformably overlain by Ordovician–Early Devonian carbonate-terrigenous passive-margin sequences. These rocks are crosscut by intrusions and overlain by a volcanosedimentary unit of the Devonian active margin. The top of the section is marked by Famennian–Visean molasse deposits onlapping onto Devonian rocks. The molasse deposits accumulated above a major unconformity reflects a major Late Paleozoic phase of folding, which is most pronounced in deformations at the edges of the autochthon, nearby the Kaim, Charysh–Terekta, and Teletskoe–Kurai fault nappe zones. Upper Carboniferous coal-bearing molasse deposits are preserved as tectonic wedges within the Charysh–Terekta and Teletskoe–Kurai fault nappe zones.Detrital zircon ages from Middle Cambrian–Early Ordovician rocks of the Anyui–Chuya fore-arc zone indicate that they were primarily derived from Upper Neoproterozoic–Cambrian igneous rocks of the Kuznetsk–Altai island arc or, to a lesser extent, from an Ordovician–Early Devonian passive margin. A minor age population is represented by Paleoproterozoic grains, which was probably sourced from the Siberian craton. Zircons from the Late Carboniferous molasse deposits have much wider age spectra, ranging from Middle Devonian–Early Carboniferous to Late Ordovician–Early Silurian, Cambrian–Early Ordovician, Mesoproterozoic, Early–Middle Proterozoic, and early Paleoproterozoic. These ages are consistent with the ages of igneous and metamorphic rocks of the composite Kazakhstan–Baikal continent, which includes the Tuva-Mongolian island arc with accreted Gondwanan blocks, and a Caledonian suture-shear zone in the north. Our results suggest that the Altai–Sayan region is represented by a complex aggregate of units of different geodynamic affinity. On the one hand, these are continental margin rocks of western Siberia, containing only remnants of oceanic crust embedded in accretionary structures. On the other hand, they are represented by the Kazakhstan–Baikal continent composed of fragments of Gondwanan continental blocks. In the Early–Middle Paleozoic, they were separated by the Ob’–Zaisan oceanic basin, whose fragments are preserved in the Caledonian suture-shear zone. The movements during the Late Paleozoic occurred along older, reactivated structures and produced the large intracontinental Central Asian orogen, which is interpreted to be a far-field effect of the colliding East European, Siberian, and Kazakhstan–Baikal continents.     

On the Evaluation of the Extremality Index EFI

The Extreme Forecast Index (EFI) calculations are performed using the ECMWF 2-m air temperature forecasts produced in the framework of the Subseasonal to Seasonal (S2S) Prediction Project. Four computation schemes are implemented using empirical and theoretical distributions of heat wave characteristics as well as the one-dimensional test statistics of histograms and linear interpolation formulas. Case studies (for different initial dates and regions) characterized by the significant air temperature anomalies in Northern Eurasia are performed using traditional forecast skill scores and the spatial verification methods to evaluate the efficiency of the proposed schemes for different threshold values of EFI. It is shown that the forecast quality can be considered satisfactory in most cases. The dependence of forecast skill on the intensity, spatial scales, and duration of temperature anomalies is revealed. Further studies should be carried out using larger samples based on several hydrodynamic models and the multimodel approach.     

Petrology of mafic lavas within the Onega plateau, central Karelia: evidence for 2.0 Ga plume-related continental crustal growth in the Baltic Shield

The Onega plateau constitutes part of a vast continental flood basalt province in the SE Baltic Shield. It consists of Jatulian-Ludikovian submarine volcanic, volcaniclastic and sedimentary sequences attaining in places 4.5?km in thickness. The parental magmas of the lavas contained ～10% MgO and were derived from melts generated in the garnet stability field at depths 80–100?km. The Sm-Nd mineral and Pb-Pb whole-rock isochron ages of 1975?±?24 and 1980?±?57 Ma for the upper part of the plateau and a SHRIMP U-Pb zircon age of 1976?±?9 Ma for its lower part imply the formation of the entire sequence within a short time span. These ages coincide with those of picrites in the Pechenga-Imandra belt (the Kola Peninsula) and komatiites and basalts in the Karasjok-Kittilä belt (Norway and Finnmark). Together with lithostratigraphic, chemical and isotope evidence, these ages suggest the derivation of the three provinces from a single large (～2000?km in diameter) mantle plume. These plume-generated magmas covered ～600,000?km² of the Baltic Shield and represent a major contribution of juvenile material to the existing continental crust at 2.0 Ga. The uppermost Onega plateau lavas have high (Nb/Th)_N?=?1.4–2.4, (Nb/La)_N= 1.1–1.3, positive ?Nd(T) of +3.2 and unradiogenic Pb-isotope composition (μ₁?= 8.57), comparable with those of modern oceanic plume-derived magmas (oceanic flood basalt and ocean island basalt). These parameters are regarded as source characteristics. The lower sequences have (Nb/Th)_N= 0.58–1.2, (Nb/La)_N= 0.52–0.88 and ?Nd(T) =?2.6. They have experienced mixing with 10–30% of continental crust and resemble contaminated lavas from other continental flood basalt provinces. The estimated Nb/U ratios of 53?±?4 in the uncontaminated rocks are similar to those found in the modern mantle (～47) suggesting that by 2.0 Ga a volume of continental crust similar to the present-day value already existed.