G. G. Matasova

A 1‐Myr record of paleoclimates from Lake Khubsugul, Mongolia

The ancient Lake Khubsugul in North Mongolia is situated at the far reach of moisture from the North Atlantic into continental Asia [Kuznetsova, 1978]. It is remote from the Pacific Ocean and shielded from the China Sea and the Indian Ocean by high mountains. Information on the paleoclimates in this territory is scarce and sometimes controversial. In winter of 2003, due to a joint project (Khubsugul Drilling Project or KDP) of the Siberian Branch of the Russian Academy of Sciences and the Academy of Sciences of Mongolia, a 53-m drilling core (KDP-1) of sediments of Lake Khubsugul was obtained. This article describes the first results of paleomagnetic and geochemical studies of this core, which was found to span the time interval of the last 1.05 Myr. The data suggest that global climate oscillations manifested themselves in repeated desiccation and filling of the lake due to changes in humidity.

Rock magnetism and magnetostratigraphy of the loess-sol series of Ukraine (Roksolany, Boyanychi, and Korshev sections)

The results of the rock magnetic and paleomagnetic studies for the Quaternary loess-sol deposits of Ukraine are reported. The magnetic properties of the rocks composing the sections in the Pre-Black-Sea Depression (Roksolany) and Volyn Upland (Boyanychi and Korshev) are compared. Based on the highly precise measurements by modern instruments, the primary magnetization component is isolated in the rocks and its polarity is reliably determined in both the loess and soil horizons. The position of the Matuyama–Brunhes boundary in the Roksolany section is determined at a depth of 46.6 m at the contact of the Lubenskii and Martonoshskii soil horizons. This is consistent with the present-day notions of the group of Ukrainian scientists about the Quaternary stratigraphy of the south of Ukraine and inconsistent with the previous results that placed this boundary at a depth of 34 m in loesses above the PK7 level.

Lithogeochemistry of rocks of the Upper Neopleistocene Ust-Oda reference section in the Irkutsk Amphitheater of the Siberian Platform

The results of study of rocks of the Ust-Oda section, one of the key outcrops of Upper Neopleistocene sediments in the Irkutsk Amphitheater of the Siberian Platform, are presented. It is shown that primary sediments were deposited in the Neopleistocene under subarid conditions and relatively high sedimentation rates. Similar contents of trace elements in all rock lithologies suggest that the provenance was unaltered during sedimentation. It is shown that variation in the sediment transport mechanism is one of the signs of changes in the paleoclimatic setting. Climatic cyclicity of the Ust-Oda section formation and succession of sedimentation setting, which were reconstructed on the basis of grain size data, correspond to variations in the petrochemical correlations and geochemical coefficients.

Magnetic Polarity Stratigraphy of the Upper Cenozoic Deposits of Near-Sea Dagestan (Russia) and the Age of the Early Paleolithic Site Rubas-1

We studied magnetic polarity in four Upper Neogene (Akchagylian stage) sections of Near-Sea Dagestan. Paleomagnetic studies have shown that Shor-Dere section is the most complete section of Late Neogene—Late Quaternary in this territory. The section Rubas-1, which contains Paleolithic artifacts, corresponds to the upper part of the Shor-Dere section, while sections Ajinour and Rubas River are likely short fragments, so their correlation with the reference section is ambiguous. A composite magnetic polarity section of Near-Sea Dagestan was constructed on the base of correlation between Shor-Dere, Rubas-1 and, in part, Rubas River sections. Magnetic polarity pattern of the composite paleomagnetic section is well correlated with the polarity zonation of Akchagylian stage for the neighboring regions of the Caspian basin (Azerbaijan and Turkmenistan), the south of the European part of Russia and the Transcaucasia (the Northern Caspian and the Lower Volga region). Such correlation of the magnetic polarity with those from startotype regions of Akchagylian stage made it possible to identify magnetic polarity zones in the composite section with the magnetic polarity chrons of the Neogene and Quaternary Time Scale (2016). We suggest that the upper part of the composite section can be correlated with Matuyama Chron including Olduvai and Reunion subchrons, while the lower part attributes to Gauss Chron with Kaena subchron. The proposed correlation provides the basis for approximate age estimates for the studied strata and supposes the age of the stone industry from Rubas-1 site not later earlier than 2 million years ago.

Rock-Magnetism and Granulometry of Late Palaeolithic Sites in the Tunka Rift Valley (Pribaikalie) as a Tool for Reconstruction of Sedimentary Environment

Geological structure, rock-magnetic properties and grain size composition of Late Pleistocene-Holocene sediments containing archaeological horizons with cultural relics have been studied in the Tunka rift valley near Lake Baikal at two archaeological sites: “Tuyana” and “Zaktui”. The closely neighboured sites are in a different geomorphological position: Tuyana is located on the valley slope, while Zaktui sits on the second terrace of Irkut river. The combined analysis of the granulometric and rock-magnetic parameters specifies the genetic deposition types and clarifies the general structure of both sections so that the sedimentation environment in the second half of the Late Pleistocene and Holocene could be reconstructed.

Hysteresis characteristics of subaeral deposits in the Baikal region

The results of rock magnetic studies in four subaeral cis-Baikalian sections of different ages and geneses are described in detail. The similarities and distinctions in the formation of the magnetic properties of the sediments are established based on the analysis of the magnetic hysteresis parameters. The mechanisms responsible for the dissimilarity of the magnetic characteristics of the rocks in the different sections are identified. The variations in the composition, concentration, and particle size of the grains of magnetic fraction as a function of climate, geomorphologic factors, and volcanism are demonstrated.

U–Th age of the Kazantsevo (MIS 5) Horizon of the Upper Neopleistocene Ust Oda reference section, Baikal Region

For the first time, the organic sediments of the Kazantsevo Horizon (Baikal Region) were characterized geochronometrically. The 230Th/U age of the buried gyttias from the Upper Neopleistocene Ust Oda stratotypical section on the Kitoi River was determined using a new version of isochronous approximation. The assemblage of all the 230Th/U age data, which were obtained taking into account the errors in the entire range from 136 to 86 kyr, indicates that most likely gyttia age is 115–104 kyr (MIS 5d). Thus, the paleontological conclusions on the Kazantsevo age of the Ust Oda Formation with buried gyttias are confirmed. Our geochronometric data supplement and make more reliable the age model of the formation of sedimentary rocks of the Ust Oda section.

The experience of using the rock magnetic methods for assessing the prospects of magnetic exploration in the territory of archaeological monuments of the Barabinsk forest steppe

The results of studying the magnetic properties of the components of the natural environment of the Barabinsk forest steppe accommodating the archaeological monuments dated to VI century B.C. to II century A.D. are presented. The rock magnetic model is constructed for a two-layer medium composed of modern soil and an underlying blanket substratum deposits (clay loam, sandy loam, sand). It is shown that the magnetism of the humic horizon of the soil depends on the topographic position and soil type, whereas the magnetic characteristics of the underlying substratum deposits are persistent throughout the studied territory. The ratio of the magnetic susceptibilities of the humus horizon to the substratum is K = 3–6 for the automorphic soil, K = 1–2.5 for semihydromorphic soil, and K = 0.8–1.0 for hydromorphic soil. Based on subdividing the studied territory in accordance with the values of K and the calculated amplitudes of the microanomalies of the magnetic field, the areas where application of the magnetic survey is highly promising, moderately efficient, and unpromising are outlined. The particular cases of the absence of magnetic anomalies above the archaeological objects, the false anomalies, and the chaotic patterns of the low-amplitude anomalies—all the situations when the magnetic survey is inefficient—are explained from the standpoint of the model.