Sofia I. Merenkova

The comprehensive comparative lithological and geochemical characteristics of the Quaternary (Middle Pleistocene-Holocene) formations of the Moscow synecli

In this paper we present a comprehensive comparative lithological and geochemical characteristics of the Quaternary (Middle Pleistocene-Holocene) formations of the Moscow syneclise within the Chashnikovo Depression. Based on the results of X-ray fluorescence analysis, the normative mineral composition was calculated using the MINLITH program. Data on the content of major petrogenic oxides and normative mineralogy for deposits of glacial, fluvioglacial, lacustrine, fluvial and eolian-deluvial genesis were analyzed using the principal component analysis. As a result of statistical processing, 3 groups were identified that are characterized by a common mineralogical composition and geochemical features. It is suggested that these groups are temporary genetic series of deposits, where the material of more ancient deposits served as a source for the formation of subsequent ones. The article discusses the issue of calculating the CIA petrochemical index as applied to these deposits.

The features of the mineral and chemical composition (major elements) of the Vendian-Cambrian rocks of the Silimkun Formation (V-Є1sl), exposed on the western side of the Upper Kalar graben syncline in the southwest of the Aldan shield, are considered. The studied rocks – sandstones and siltstones, belong to arkoses and subarkoses. According to their chemotype, they correspond normosilites and myosilites. In terms of the alkaline modulus, the studied silites are hyperpotassium and serve as a fairly striking example of the products of Precambrian arid weathering. The standard mineral composition, its variations, the validity of calculations based on petrographic research data, the problems of using climate indices and lithochemical diagrams aimed at reconstructing climatic changes in the geological past are discussed. Chemical Index of Alteration (CIA) index values range from 49, which corresponds to a virtually unchanged rock, to 67. The average is about 58. Minor changes in the index value for this sample are associated primarily with variations in the content of illite cement and muscovite. Robust Weathering index (RW) values range from 37 to 68 (with an average of about 57).

An astrochronological (cyclostratigraphic) binding of the lithological and geochemical characteristics of Pliocene-Quaternary sediments of the Eurasian sections to the Milankovich cycles (eccentricity, obliquity of the ecliptic, precession) was carried out, an analysis of the relationship between the established variations in climate and paleotemperature with the moments of coincidence of different-order cycles of eccentricity and their paleoclimatic characteristics was given. The results of the implementation of the results obtained during the practice in geology at the Moscow State University in Chashnikovo are shown. During the research, materials from the exposition space of the Department of Regional Geology and Earth History and the Museum of Earth Science were used. The results of the study were used in conducting an educational practice in geology in Chashnikovo, and can also be used in the dismemberment and regional and global correlation of sections, in conducting geological surveys, creating cyclostratigraphic scales of the plains and mountainous regions of Eurasia, as well as in the creation and further development of the exposition space of museums — Moscow State University Gymnasium for example.

Astrochronological (cyclostratigraphic) connection of the lithological and geochemical characteristics of the Pliocene–Quaternary deposits of the Eur

There are presented the results of geochemical studies of the Vendian-Cambrian terrigenous rocks in the Upper Kalar depression– sandstones of the Silimkun formation, exposed in the floodplain of the Kilcheris River (left tributary of the China River), in the upper reaches of the Kemen River. The rocks are enriched in Sc, Cr, Nb, V, Co, Ni, as well as in Mo and heavy rare earth elements. This study demonstrates a rare pairwise correlation between Mo and Cr. A strong positive correlation of P with Nb, Ti and Fe is indicative of P sorption phenomena in alteration products of titanium minerals (e.g. leucoxene). It has been found that the sandstones of the Silimkun Formation were formed as a result of the destruction of granitoids of the Kalar massif – presumably granite porphyries and fine-grained porphyritic biotite granites. The influence of the gabbro-norites of the Chiney complex, enriched in trace elements commonly found in rocks, is less pronounced.

The astrochronological (cyclostratigraphic) relationship of the lithological and geochemical characteristics of Quaternary deposits to the Earth’s or

An astrochronological (cyclostratigraphic) binding of the lithological and geochemical characteristics of the Quaternary deposits to the cycles of eccentricity of the Earth’s orbit is carried out, an analysis of the relationship between the established variations of climate and paleotemperature with the moments of coincidence of different-order cycles of eccentricity and their paleoclimatic characteristics is given. The results of introducing the data obtained into the exhibition space of natural science museums are shown.

The Evenki Formation of the Siberian Platform is studied on the right bank of the Podkamennaya Tunguska River near the settlement of Sulomay (Evenki municipal district of Krasnoyarsk region). The structures and textures of composing sediments is described. The main petrogenic oxides are identified and the normative mineral composition is calculated following this identification. The increase of terrigenous components in the strata indicates periods of enhanced erosion in the provenance area, which is the Yenisei Ridge. In turn, the increased contribution of feldspars in the middle part of the section shows intensification of physical weathering in arid conditions. The principal hypotheses on the origin of the Evenki Formation as well as of other recent and ancient tidal flat and sabkha facies are outlined. We suggest that the facies of the Evenki Formation under study have been accumulated mostly under intertidal and, possibly in part, under lower supratidal conditions, which alternated depending on eustatic fluctuations in the basin. A conceptual model of the genesis of the Evenki Formation on the Siberian Platform is developed.

The Evenki Formation of the Siberian Platform has been studied on the right bank of the Podkamennaya Tunguska River near the Sulomai settlement (Evenki mun