Vol 57, No 6 (2019)

A representative suite of 276 samples was used to study the isotopic and elemental geochemistry of kerogens from the Bazhenov horizon (Bazhenov Formation and its age equivalents) of the western Siberian sedimentary basin and to map the variations in the elemental composition of kerogen in the area. The elemental composition of the kerogen was used to determine the types of organic matter (H and C contents), the initial components of the living matter that were the source of the kerogen (H and N contents), the diagenetic history of organic matter (S content), and the level of catagenetic transformation of the kerogen (C and O contents). Kerogen from the central, western, and southern parts of the western Siberian basin, up to the pinch-out boundary of the Bazhenov horizon, shows strong enrichment in hydrogen (up to 8–9%) and ¹²С (δ¹³С‰ from –35 to –29), suggesting its derivation from polymer lipids of aquatic origin. Kerogen from the Bazhenov horizon (catagenetic grade MC₁) in the northeast of the basin contains much lower hydrogen concentrations (2–4%). A map of the types of organic matter in the Bazhenov horizon is constructed.

This paper discusses the geochemical and petrological characteristics of acid volcano-plutonic suite of rocks exposed in Riwasa and Nigana areas of Malani Igneous Suite (MIS), Northwestern India. Geochemically, these acidic rocks having peraluminous and alkalic to alkali-calcic nature and classified as volcanic phase (Riwasa rhyolites), plutonic phase (Nigana granites) and dyke phase (micro-granites). Petrographically, rhyolites show porphyritic, granophyric, glomeroporphyritic, aphyritic, spherulitic and perlitic textures whereas granites show hypidomorphic, granophyric and microgranophyric textures. They are high in silica, A/CNK, total alkalis, Fe/Mg, Ga/Al, Zr, Rb, U, Th, Cu, REEs (except Eu) and low in CaO, MgO, Sc, Cr, Ni, Sr and Eu abundances, which have affinity with A-type granitoids. Their chemistry also support that they are high heat production (HHP) granitoids and their crustal origin. The enrichment of trace elements indicates a genetic link between fractional crystallization of silicate minerals and post magmatic fluid alterations in magmatic chamber. Negative anomalies of Ti, P, Sr and Eu in the multi-element spider diagrams indicate that the emplacement of these granites and associated acid volcanics were controlled by fractionation of feldspar (alkali and plagioclase) and crustal contamination in the magmatic melt arise upward. Normative values of silicate oxides further suggests that these rocks are formed between 2–7 kb pressure ranges and may be emplaced from shallow to greater depth ranges (15–30 km and 450–900°C). Furthermore, geochemical features in acidic rocks such as strong linear positive correlation between LREE, Zr, Nb, Ga, Y and Rb emphasize that the behavior and enrichment of these elements are largely controlled by post-magmatic processes in plume related associations. Hence, the geochemical data presented here, are therefore consistent with an intraplate, co-magmatic and A₂-subtype granite field emplaced in extensional tectonic regime of MIS.

The paper analyzes the bulk chemical composition and distribution of the fields of syn-rift clayey rocks on a number of discriminant paleogeodynamic diagrams. It is shown that the syn-rift clayey rocks, in general, demonstrate significant variations in the bulk chemical composition. For example, the average SiO₂ content varies from 44.74 to 66.42 wt %, the average Al₂O₃ content varies from 16.62 to 29.92 wt %, and the K₂O_aver is in the range 0.24 … 5.77 wt %. Based on the distribution of the data points of syn-rift clayey rocks from various objects in the F1–F2 diagram, it can be assumed that the sources of fine aluminosiliciclastic material were magmatic and sedimentary rocks of a wide composition range. The substantial overlap of the fields of various objects in the classification diagrams [(Na₂O + K₂O)/Al₂O₃]–[(Fe₂O_3tot + MgO)/SiO₂] and K/Al–Mg/Al indicates, in general, the similar composition of syn-rift fine-grained clastic rocks of various types of riftogenic structures. The localization of the composition fields of the clayey rocks of different riftogenic structures in such discriminant paleogeodynamic diagrams as K₂O/Na₂O–SiO₂/Al₂O₃ and SiO₂–K₂O/Na₂O suggests that they cannot be used to discriminate reliably between syn-rift clayey rocks and fine-grained clastic rocks of other geodynamic environments. The position of the syn-rift clayey rocks fields from our database in the diagram DF1–DF2 has its own characteristics. In most cases, they occupy a particular position in the areas characterizing collision and rifting environments, and a number of fields are located in all three classification areas of this diagram. A significant part of the midpoints of the syn-rift clayey rocks is localized in the collision field in the DF1–DF2 diagram. All these facts indicate that the DF1–DF2 diagram also cannot determine the geodynamic nature of terrigenous associations.

This paper presents evidence on the possible impact of aerobic and anaerobic microbiological processes on uranium migration in upper aquifers polluted by sulfates and nitrates at the Novosibirsk chemical concentrate plant (PAO NCCP). Uranium can be immobilized in local areas with high contents of organic substances, and the most important microbiological process is a decrease in redox potential owing to aerobic respiration, which can be followed under anaerobic conditions by redox-dependent uranium reduction in areas with negative Eh values. Moreover, in the presence of sufficient amounts of sulfate ions, further anaerobic processes of microbial sulfate and iron reduction result in the formation of iron sulfide, which serves as an antioxidant buffer in the case of oxygen infiltration into the sediment and transforms to molecular sulfur or sulfate preventing uranium oxidation.

The hypothesis of silicate phosphatization under supergene zone conditions was experimentally tested. To extend our previous experimental work on clay minerals (kaolinite and montmorillonite), we studied the phosphatization of aluminosilicates of other structural types (hornblende, orthoclase, and labradorite) interacting for nine months with 1.2–6.0 mM orthophosphate solutions over a wide range of solution acidity. Nearly linear dependence common for all minerals was found between variations in phosphorus and silicon concentrations in the solution: Δ[Si] ≈ –Δ[P]. It was demonstrated that aluminosilicates can be replaced by phosphate minerals at relatively minor concentrations of dissolved phosphorus corresponding to phosphate abundances in soil solutions.