— This work presents the results of the mineralogical, crystallochemical, and geochronological study of globular phyllosilicates (GPS) of glauconite–illite series from the Bakeevo Formation....

Complex paleontological and isotope-geochronological study of clastic sediments of the Vychegda Depression (Mezen syneclise) has been carried out on samples retrieved from the Keltmen-1 borehole drilled in the junction zone of the Russian and Timan-Pechera plates. The stratigraphic structure of the clastic unit in the depth interval 1874–2910 m has been perfected. At the base of the unit, the new Okos Formation has been described: glauconite from it was dated by Rb-Sr to 807 ± 8 Ma. The obtained microphytologic characteristic of the upper part of the section is in agreement with lithological and geochemical data, allowing recognition of two Upper Vendian Formations: Ust-Pinega and Mezen. The stratigraphic hiatus between the Upper Riphean and Vendian deposits in the Keltmen-1 borehole reaches 200–250 M.y. For the first time Ediacaran acanthomorph microfossils of the genera Appendisphaera and Tanarium have been found in the high horizons of the Upper Vendian, proving their wider stratigraphic distribution.

Bentonite clays have unique properties that determine their use as the main component of engineered barrier systems (EBS) for the isolation of radioactive waste. At present, the Russian Federation is elaborating the concept of deep geological disposal of radioactive waste in crystalline rocks of the Yeniseisky site, where bentonite clays play an important role in ensuring the safety of the repository for a long period of time. This work demonstrates the first results of short-term laboratory experiments (1 and 3 months) on the thermochemical interaction of bentonite and concrete in the presence of synthetic water at an elevated temperature. These experiments will help predict the effect of EBS materials on montmorillonite. Bentonite from the 10th Khutor deposit (Russia) and Portland cement were used in the experiments. At the first stage of the experiments, solutions were obtained after leaching the concrete with a synthetic groundwater solution for 1 month at 90 °C. At the second stage, the interactions of the obtained solutions with bentonite at 90 °C were studied. As a result of the experiments, the processes of concrete leaching were revealed, which changed the composition and acidity (an increase in the pH from 6.1 to 12.1) of the synthetic water and led to an increase in the porosity of the material in contact with the solution. However, no dissolution of montmorillonite was observed, and the changes were quite small. The research results show the high stability of bentonite from the 10th Khutor deposit under model conditions, which was confirmed by modeling. Thus, we can say that at pH ≈ 12 and at elevated temperatures, montmorillonite retains a stable structure for a long time, which is important for ensuring the safety of disposal in general.

The results of U–Th–Pb LA-ICP-MS dating of detrital zircons from oolitic limestones of the lower subformation of the Uk Formation are presented. The Uk Formation represents the upper level of the Late Riphean stratotype in the Southern Urals. The obtained data show that half of the detrital zircons were supplied by eroded Archean and Paleoproterozoic complexes in the adjacent territory of the East European Platform. Igneous complexes (Berdyaush, Ryabinovsky, Gubensky, and Akhmerovsky granitoids; 1.35–1.40 Ga) located in the Bashkirian meganticlinorium could supply less than a tenth of grains. Nevertheless, the Mesoproterozoic (Middle Riphean) rocks (1.13–1.40 Ga) were the main source of detrital zircons in the Early Uk time. A potential Mesoproterozoic source could have been either the Fennoscandian rapakivi granites (1.44–1.56 Ga) and the rocks of the Sveconorwegian (Grenville) orogenic belt (1.13–1.16 Ga) or an unknown continental block joined during the Grenville orogeny.

The paper presents an overview of crystal-chemical peculiarities of the previously studied globular dioctahedral 2 : 1 layer silicates of the glauconite-illite compositions from the Upper Proterozoic sections in northern Siberia (Anabar and Olenek uplifts). Lithomineralogical peculiarities of the glauconite-bearing rocks are discussed. Geochronological data on some samples are given. Monomineral fractions of grains were studied with the modern chemical and physical methods (X-ray diffraction, oblique-texture electron diffraction (OTED), scanning electron microscopy, IR and Mossbauer spectroscopy, classical chemical and microprobe analyses, and others). Low-charge dioctahedral 2 : 1 layer silicates were classified with consideration of the IMA NC and AIPEA NC recommendations (Rieder et al., 1998; Guggenheim et al., 2006). This classification showed that the studied globular Al- and Fe-bearing varieties include a continuous isomorphic glauconite-illite series. Intermediate layer silicates beyond the IMA NC and AIPEA NC classification are assigned to Al-glauconites (Fe-illites). True illites should be supplemented with adjectives “globular” or “platy,” because green globules and the fine-dispersed Al-bearing clay minerals are traditionally recognized as “glauconite” and “illite,” respectively.