Vol 55, No 6 (2017)

Holocene sequences of the Russian Arctic shelf seas are controlled by a combination of three main factors: deglaciation of the Late Pleistocene Barents–Kara ice sheet, global sea-level rise, and river runoff from Eurasia. Sedimentation in the Kara Sea is mainly defined by two latter factors. The lithological, grainsize, mineralogical, and micropaleontological compositions of the Holocene sequences of this basin have been widely studied, but only a few works report geochemical data. This paper considers comprehensive geochemical data on two cores from the Yenisei transect obtained during cruise of the R/V Akademik Petrov in 2000. Both the cores were dated by radiocarbon accelerator mass spectrometric method (AMS ¹⁴C) and analyzed using XRF and ICP MS methods. The study revealed and described differences in their chemical composition, which are caused by different facies settings of accumulation, their grain size composition, and influence of river run-off.

Fe–Ti oxides (magnetite, Ti-magnetite, ilmenite, and associated high-Al spinel) in the ferrogabbroids of the Middle Paleoproterozoic Elet’ozero syenite–gabbro intrusion are intercumulus minerals usually surrounded by coronitic rims of two types. The first type usually represents multilayer amphibole–biotite ± olivine coronas along contacts of Fe–Ti oxides with cumulus moderate-Ca plagioclase and more rarely, clinopyroxene. Two-layer rim is developed in contact with high-Ca plagioclase; the inner rim consists of pargasite and spinel, while the outer rim is made up of sadanagaite and spinel. The second type is represented by two-stage coronitic textures developed along boundaries of olivine and Fe–Ti oxide clusters with plagioclase. Initially, the olivine was surrounded by orthopyroxene rim, while Fe–Ti oxides were rimmed by pargasite with thin ingrowths of high-Al spinel (hercynite). At the next stage, the entire cluster was fringed by a common symplectite reaction rim, the composition of which also depended on the composition of plagioclase matrix: the spinel–sadanagaite rim was formed in contact with high-Ca plagioclase, while pargasite–muscovite–scapolite rim was formed in contact with moderate-Ca plagioclase. The formation of the outer rims occurred after hydration of the inner parts of coronas around olivine and oxides within the clusters. It is suggested that the Fe–Ti oxides and surrounding coronitic rims were microsystems formed by crystallization of drops of residual hydrous Fe-rich liquid.

A new technique is suggested for evaluating the pH buffer capacity of natural aquatic systems (as exemplified by small lakes in western Siberia) with regard for the pH values of the lake waters and the concentrations of the hydrocarbonate ion and anions of humic acids,. The acid-neutralizing capacity evaluated for small lakes in western Siberia by conventionally used techniques (which was suggested by Norwegian researchers) is compared with evaluations by the technique suggested by the authors. Criteria are suggested for quantifying the immunity of natural waters to acidification in various natural climatic zones in western Siberia.

Analysis and calculation techniques of geochemical background concentrations of chemical elements in various systems is of paramount importance for applied geochemistry. Herein we assume the geochemical background as the average of natural variations in the concentrations of chemical elements determined at a territory that highly probable does not host any natural and/or anthropogenic sources of contaminating chemical elements. In the context of determining geochemical background, our research was focused on determining the concentrations of heavy metals in soils in the city of Yerevan with the application of an integrated approach. Comparison of the obtained background values with the mean concentrations of elements in the upper continental crust yields representative data, and the application of various statistical tests (±3σ, ±2σ, and boxplots) is proved to equally efficient.

The β-factors of corundum were estimated on the basis of DFT calculations of vibrational frequency changes due to ¹⁶O–¹⁸O isotope substitution in a harmonic approximation using an all-electron Gaussian-type basis set and the B3LYP hybrid functional (the CRYSTAL program). Calculations were performed accounting for eight phonon wave vectors within the first Brillouin zone. The results are approximated by the relation 1000ln β_crn = 9.19874x–0.12326x² + 0.00213x³ (x = 10⁶/T(K)², 400 < T(K) < 1300), which can be used in isotope geochemical studies in combination with the known temperature effects on the β-factors of other phases.