Distribution of Heavy Metals in Gray Silts in the Volga Cascade of Reservoirs

Water Resources - The concentrations of heavy metals in gray silts were analyzed in the Volga cascade of Reservoirs (June 2016, R/V Akademik Topchiev, Borok Village–Astrakhan City). The mean...     

Pelitic rocks from the molasse formation of the Southern Ural segment of the Uralian foredeep: Lithogeochemistry,provenance composition,and paleotectonic reconstructions

In this paper, we consider the lithogeochemical characteristics of pelitic rocks from the molasses (Late Permian) of the Southern Ural segment of the Uralian foredeep. The examination of mudstones showed that they contain high and variable amounts of secondary carbonate minerals and, consequently, high and variable CO₂, which complicates the use of traditional lithochemical diagrams for their classification and genetic reconstructions. On the other hand, the lithogeochemical characteristics of the pelites (as well as psammites) provided evidence on the compositions of provenances in paleocatchments. High Cr and Ni contents indicate the presence of ultrabasic rocks in the provenances, and the distribution of Cr/Ni values suggests insignificant chemical homogenization of aluminosilicate fine-grained clastic materials and, consequently, short transport distances. The dominant first-cycle nature of the clay rocks is indicated by the relations of major oxides and various lithochemical indexes. The heterogeneous and complex composition of the end-Permian provenance is supported by the covariation diagrams of indicator trace element ratios.     

Specific features of the distribution of trace and rare earth elements in recent bottom sediments in the lower course of the Severnaya Dvina River and White Sea

The paper discusses results of the lithogeochemical examination of recent bottom sediments in the lower course of the Severnaya Dvina River and White Sea. It has been established that the average concentration of several trace elements (Hf, Sc, Co, Y, Ni, V, Cr, Zr, Ba, and others) therein correlates with the content of the silt-pelite fraction. Maximal concentrations of the majority of above elements are confined to the silty-clayey sediments at the Basin/Dvina Bay boundary. They localized near the coastal zone only for some clastophile (Zr, Cr, and others). Typical values of the hydrolyzate module, chemical index of alteration, and Al₂O₃/SiO₂ ratio in the aleuropelitic and pelitic sediments of the Severnaya Dvina River delta, Dvina Bay, and the Dvina Bay Basin boundary suggest that these sediments are confined to sufficiently cold climate settings. Data points of sediment composition in discriminant paleotectonic diagrams are scattered over a large field probably due to high contents of the weakly weathered plagioclases, micas, and amphiboles, as well as the hydrogenic process promoting the accumulation of Fe and Mn. The PAAS-normalized spectra of rare earth elements (REE) in bottom sediments of the Pinega and Severnaya Dvina rivers, marginal filter of the latter river, Dvina Bay, and the Dvina Bay Basin boundary are similar to the REE distribution in clayey rocks of the ancient platform cover (except for a slight positive Eu anomaly). The REE systematics and distribution pattern of compositional data points of recent bottom sediments in the Gd_N/Yb_N-Eu/Eu* and Eu/Eu*-Cr/Th diagrams and values of several indicator ratios of trace elements suggest that the studied rocks were formed by the mixing of clastic materials from geochemically contrast provenances: northwestern provenance (Kola-Karelia geoblock), which is mostly composed of the Archean and Early Proterozoic crystalline complexes, and the southeastern provenance (northwestern periphery of the Mezen syncline), which is almost totally composed of Phanerozoic sedimentary rocks. The latter provenance likely played a crucial role in the geochemical signature of recent bottom sediments over a significant area of the White Sea.     

Stratigraphic position and significance of carbonate rocks related to neoproterozoic glacial horizons of the Urals

Some Neoproterozoic glacial deposits of the Urals associate with cap carbonates and carbonateterrigenous members. In addition, carbonate lenses and layers are observed in glacial series. Cap carbonates are characterized by quite variable textures and structures; because of this, it is considered that they were formed under different conditions and in the course of various processes accompanying glaciations and deglaciations. Cap carbonates have a regional stratigraphic significance. Multiplicity and complex age structure of glacial events in the Neoproterozoic do not allow us to apply cap carbonates for interregional correlations and construction of the general stratigraphic scale of the Neoproterozoic without additional biostratigraphic, geochronological, and chemostratigraphic control.     

New Data on the Age of Metamorphic Rocks from the Granite-greenstone Ruker Terrane (Southern Prince Charlies Mountains,East Antarctica)

Doklady Earth Sciences - This work presents results of isotope studies of primary igneous and sedimentary rocks of Mawson and Menzies series from the southern Prince Charles Mountains, East...