Introduction

The Late Cenozoic is the time of the emergence and evolution of man and human society. The development of ancient man is closely connected with changes in the natural environment and climate: they significantly influenced the living conditions and lifestyle, the choice of places of existence, the possibilities and ways of settlement, the development of adaptation to the environment, and biological evolution. The reliability of information about the patterns of changes in the natural environment and climate, the sequence of stages of human development and human society, and possible ways of its settlement is determined by the state of knowledge of the Upper Cenozoic stratigraphy and chronology. Establishing the exact stratigraphic position and determining the geological age of Paleolithic sites depends on the possibility of conducting detailed stratigraphic studies of the surrounding sediments. The need to develop a detailed stratigraphy of the Upper Cenozoic of Western Siberia for archaeology is due to the recent availability of data that make it possible to significantly lengthen the time of human appearance in this territory (Derevyanko, 2005). The south of Western Siberia is one of the few regions in the world where the continental Upper Cenozoic is most fully represented, with rich paleontological characteristics and representative dating material that provide reliable recording of changes in the natural environment and climate. The geological sections of the Cenozoic in this territory are unique archives containing huge information about the history of the formation of the modern climate and the natural environment of this territory. The Upper Miocene and Pliocene of the plain is composed of lacustrine, riverine, and sub-aerial deposits. In the south-east of the plain, there are unique loess-soil sections that clearly reflect the climatic changes of the Quaternary period. The record of climatic events established in the loess-soil layer of Western Siberia is comparable to the oxygen isotope scale of oceanic precipitation.

The Upper Cenozoic stratigraphy of southern Western Siberia is poorly understood. Therefore, the article considers only some of the main problems of stratigraphy of this region and outlines ways to solve them based on recent data. New materials make it possible to make significant adjustments to the stratigraphy of the considered interval. They relate to the boundaries of the Miocene and Pliocene, Pliocene and Quaternary systems in the region, as well as the stratigraphy of the Eopleistocene and subaerial Neo-Pleistocene.

This work was supported by the Russian Foundation for Basic Research (grants). 01 - 05 - 65085, 02 - 05 - 64126, 04 - 05 - 64486, 06 - 05 - 64049, 07 - 05 - 01109).

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Boundaries of common stratigraphic units in continental regions

One of the main problems that arise when developing a scale for any stratigraphic interval is drawing and correlating the boundaries of common stratigraphic units. Accurate drawing of these boundaries in specific regions that are at different distances from the boundary stratotypes, and even more so in intra-continental areas, is a difficult task. The more complex the geological structure of a region, the more difficult it is to reconstruct its particular geosystems and bring their changes and rearrangements into a single chronological sequence. The character of feature changes at stratigraphic boundaries varies along the strike both on the Earth's scale and in each specific region. The boundaries of general stratigraphic units established along the boundaries of the development of marine fauna groups are difficult to correlate with the boundaries of changes in continental faunas and floras. Therefore, most of the boundaries of common stratigraphic units in Cenozoic deposits of intracontinental regions are drawn rather conditionally. Nevertheless, the integrated use of lithological, paleontological, paleomagnetic, and geochronological data makes it possible to map out some cross-sections. certain levels that approximate the boundaries of general Cenozoic subdivisions. To ensure better recognition of the boundaries of common stratigraphic units in other facies or in other paleobiogeographic regions, the "Supplements to the Stratigraphic Code of Russia" provide for the use of auxiliary stratigraphic levels - auxiliary stratotype points that are subordinate to the points of global stratotype boundaries. The allocation of such sections makes it possible to ensure the stability of the boundaries and volumes of common stratigraphic units in specific regions. Tracing isochronous levels, which are the boundaries of standard divisions of the General stratigraphic Scale, in continental sediments is possible only on the basis of the principle of chronological interchangeability of signs by S. V. Meyen (1989). Sections where, using this principle, it is possible to draw fairly accurately the boundaries between the main divisions of the General Scale and where there are stratigraphic features that have the greatest correlation potential and make it possible to trace these boundaries over significant distances in the region, should be taken as regional stratotypes of the boundaries of general stratigraphic divisions.

The recently obtained comprehensive data on the detailed structure of Cenozoic sections of Western Siberia, their biostratigraphic and paleomagnetic characteristics allowed us to identify specific sections where the boundaries between the Miocene and Pliocene, Pliocene and Pleistocene are fairly accurately drawn on the basis of the principle of chronological interchangeability of features. These sections contain stratigraphic features that, having a significant correlation potential, make it possible to trace these boundaries over significant distances in the region.

Miocene-Pliocene boundary

The lack of a complete sequence of sedimentation at the Miocene-Pliocene boundary in North and Central Asia, as well as precise criteria for drawing the Miocene-Pliocene boundary, has long made it difficult to identify it. Boundary deposits in various regions of the world also often belonged to either the Miocene or Pliocene division of the Neogene system. After deep-sea drilling of ocean sediments, the creation of the Neogene continental scale of Western Europe, and the ratification in 2000. The International Union of Geological Sciences points of the global stratotype of the Zanklian stage boundary and, accordingly, the lower Pliocene boundary at the base of the Trubi formation in the Eraclea Minoa section (Van Cowering et al., 2000) have significantly increased the accuracy of drawing this boundary in different regions. According to magnetostratigraphic and biostratigraphic studies (Zijderveld et al., 1986;Hilgen and Langereis, 1988; Hilgen, 1991a, 6; Channell, Rio and Thunell, 1988; Van Cowering et al., 2000), the Miocene-Pliocene boundary drawn at the base of the Zanklium in the Mediterranean lies in the lower reverse part of the Zanklium basin. parts of the Hilbert chron, slightly lower than the Tver subchron (subchron C3p4p). It corresponds to the restoration of open sea conditions in the Mediterranean after the Messina salinity crisis. This allows us to consider the border more event-related than biostratigraphic. Beginning of the Pliocene at the base of the Zanklium in the Eraclea Minoa section (astronomical age 5.33 Ma) corresponds to the 510-th solar cycle calculated from the present [Lourens et al., 1996; Van Cowering et al., 2000].

The most accurate correlation of this boundary to the intracontinental regions of North and Central Asia is possible with the combined use of paleontological, paleoclimatic, and paleomagnetic data. According to many researchers, the restoration of marine conditions at the border

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The Miocene and Pliocene periods in the Mediterranean Sea are associated with" instantaneous " glacioeustatic transgression caused by climate warming (Zubakov, 1990; Chumakov, 2000; Kastens, 1992; Kastens and Mascle, 1990; McKenzie and Sprovieri, 1990; Mtiller, Hodell, Ciesielski, 1991). In Antarctica, on the Antarctic Peninsula, Pecten conglomerates, reflecting warmer conditions than at present, are dated by strontium isotopes in the range of 3.5-5.3 Ma (Dingle, McArthur, Vroon, 1997). A detailed record of climate changes for the terminal Miocene and Pliocene was obtained from oxygen isotopes in deep-water column 846 in the equatorial Pacific Ocean off the east coast of Central America (Shackleton, Hall, and Pate, 1995). The boundary between the Miocene and Pliocene, according to N. D. Shackleton and his co-authors, at the level of 5.33 Ma corresponds to the event of high ocean level standing.

In the Neogene Mammalian scale of Western Europe, compared with the magnetochronological scale (Agusti et al., 2001), the Miocene-Pliocene boundary is located in the upper part of the MN 13 mammalian zone, slightly below the base of the MN14 zone. The boundary of these Neogene mammalian zones coincides with the upper boundary of the C3p4p subchron (Tvera), which is 4.9 Ma old. The main criterion for drawing the lower boundary of the MN 14 zone is the first appearance of the genus Promimomys in Western Europe (Agusti et al., 2001). Unfortunately, a detailed sequence of species of a single phylogenetic lineage of the genus Promimomys in Europe, linked to the magnetochronological scale, has not been developed. This greatly complicates the determination of the position of fauna localities in the magnetostratigraphic scale and the correlation of European and Asian sections.

The most suitable region for accurately drawing the Miocene-Pliocene boundary in North and Central Asia is the south of the West Siberian Plain. Here, one of the most detailed continental sedimentation sequences of the Upper Miocene and Pliocene is revealed, which has a good paleontological characterization (remains of large and small mammals, freshwater and terrestrial mollusks, ostracods, and plants) and fairly fully reflects the geological, paleobiological, and paleoclimatic events of this interval (Zykin and Zykin, 1983, 1984; Zykin and Zykin, 2004 Zykin, Zazhigin, and Prisyazhnyuk, 1987, 1989a, b; Zykin, Zazhigin, and Kazansky, 1991, 1994]. The high level of development of the terminal Miocene and Pliocene stratigraphy of this region allowed V. A. Zubakov (1990) to propose this sequence as a stratoetalon of the specified interval for the whole of Central Asia. After the discovery of a species of small mammals Promimomys insuliferus (Kowalski) in the former stratotype of the Bescheul horizon near the village of By identifying the corresponding biostratigraphic level and clarifying the sequence of sedimentation and the faunas of small mammals and freshwater mollusks of the Upper Miocene and Pliocene (Zykin and Zazhigin, 2004), a more detailed correlation of this interval with the well-characterized paleontological sections of this interval in Western Europe became possible. Unfortunately, the predominant lateral stratification of the Upper Miocene and Pliocene of this region does not allow us to obtain a complete stratigraphic sequence in one section. In this regard, the stratigraphic sequence of the terminal Miocene and Lower Pliocene of the Omsk Irtysh region is proposed as an areal regional stratotype of the Miocene-Pliocene boundary.

In the Upper Miocene and Lower Pliocene interval in the Omsk Irtysh region, the Novostanichnaya, Rytovskaya, Isakovskaya, Peshnevskaya, Krutogorskaya, Bitekeyskaya, and Livenskaya formations are distinguished with distinct paleontological and paleomagnetic characteristics (Table 1). Among the small mammals in the sediments of these formations, the background species are representatives of the vole subfamily, some forms of which form a distinct phylogenetic sequence and form a distinct phylogenetic sequence. they characterize stratigraphic units of different ages. The Isakovskaya Formation is characterized by P. insuliferus (Kowalski), the Peshnevskaya Formation is characterized by P. peshnioviensis Zazhigin and P. antiquus Zazhigin, the Krutogorskaya Formation contains P. cf. dawakosi Weerd, and the Bitekey and Livenskaya formations contain remains of P. gracilis (Kretzoi).

The oldest species of the Promimomys genus, P. insuliferus, was widely distributed in Eurasia. Its remains are known from France (Michaux, 1971), Greece (Weerd, 1979), Poland (Agadzhanyan and Kowalski, 1978), and the Russian Plain (Agadzhanyan and Yerbayeva, 1983; Wangenheim, Pevsner, and Tesakov, 1995; Upper Pliocene..., 1985; Topachevsky V. A., Nesin, and Topachevsky I. V. Agadzhanyan and Kowalski, 1978] and in Siberia up to Olkhon Island on Lake Baikal (Zykin and Zazhigin, 2004; Pokatilov, 1985). This species most reliably defines the lower Pliocene and is considered by many researchers to be the base of the MN 14 zone.

Reports of an older geological age of the genus Promimomys than P. insuliferus require revision. The presence of remnants of the genus Promimomys in the sediments of the Novostanichnaya and Rytovskaya Formations (Zazhigin and Zykin, 1984) was not confirmed by new rich collections of rodent remains. The fauna localities from these formations contain remains of the genus Prosomys Shotwell, described from finds from the Hemphilic deposits of North America

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Table 1. Pliocene stratigraphic scheme of the southern West Siberian Plain

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[Shotwell, 1956; Reperming, 1968]. According to Ch. Repenning, the names Prosomys and Promimomys are synonymous. Currently, the genus Prosomys in the Old World is found only in Western Siberia.

Presence of representatives of the genus Promimomys in Pontus of Ukraine [Prisyazhnyuk and Shevchenko, 1987; Prisyazhnyuk et al., 1994; Fejfar et al., 1997] was refuted by V. A. Nesin [1996], who identified here a new genus Baranarviomys, which, according to the structure of the last lower molar, cannot be an ancestor of the genus Promimomys. Promimomys sp. from the Muguren locality (Wangenheim, Pevsner, and Tesakov, 1995), represented by a single first lower molar, has no characteristic generic features and cannot be accurately identified.

The incompleteness of the paleontological data on small mammals does not allow for a sufficiently definite correlation of Miocene-Pliocene boundary continental deposits in Eastern Europe, as well as tracing it to the intracontinental regions of Northern Asia. Taking into account that the known representatives of the genus Promimomys in Western Europe, where the most detailed and accurate correlation of the continental scale with the reference Mediterranean sequence of the Neogene is possible, appear significantly above the Miocene-Pliocene boundary, this boundary should be drawn in the interval below the Isakovskaya formation of the Omsk Irtysh region, which belongs to MN 14 of the Neogene mammalian scale (Zykin and Zazhigin, 2004]. Having narrowed the interval of the stratigraphic scale, we will consider the paleoclimatic and paleomagnetic data of the Novostanichnaya and Rytovskaya formations.

Novostanichnaya formation in its most complete section near Omsk (pos. Novaya Stanitsa) on the Irtysh River, which is a stratotype, represents a complete cycle of lacustrine sedimentation, composed of gray-colored sediments with a thickness of 17 m. The lower part of the cycle was formed under humid conditions, while the upper part was probably formed under semiarid conditions during overgrowth and filling of the lake basin. The formation has a distinct paleontological characteristic. The fauna of small mammals from the basal horizon of the Novostanichnaya formation was initially assigned to the earliest stage of Ruscinia (Zykin and Zykin, 1984; Zykin, Zykin, and Prisyazhnyuk, 19896). Currently, this fauna is placed by V. S. Zazhigin in the upper part of the Turolian (upper part of the MN 13 zone), mainly due to the presence of the genus Prosomys, as well as Lophocricetus (Paralophocricetus) afanasievi Savinov [Zazhigin et al., 2002]. The presence of a large number of Palearctic representatives (up to 45 %) among thermophilic Sino-Indian and West Siberian freshwater mollusks (55 %) and hydrophilic elements among terrestrial mollusks indicates a colder and wetter climate in the volcanic period than in the subsequent Rytovian period. Paleomagnetic studies of the stratotype of the volcanic formation (Wangenheim, Pevsner, and Tesakov, 1995; Gnibidenko, 1989, 1990) showed that the lower part of the formation, consisting of light gray fine-grained sand and siltstone, is directly magnetized, while the upper part, composed of dark greenish-gray clays with carbonate nodules, is inversely magnetized.

The Rytovskaya formation, which also represents a complete sedimentation cycle with a thickness of up to 12 m, was formed in much warmer climatic conditions. Its lower part is composed of both river sediments (sections near the villages of Cherlak and Lezhanka, near the city of Pavlodar on the Irtysh) and lake sediments (section near the village of Cherlak and Lezhanka, near the city of Pavlodar on the Irtysh). Borki on Ishim), usually painted in brownish-red and light brown tones. Previously (Zazhigin and Zykin, 1984) in the section near the village of Cherlak, as well as in the section near the village of Cherlak. New Stanitsa, the presence of the genus Promimomys was indicated, which forced us to assume the Ruscinian age of the Rytovo formation. Revision of voles from the Cherlak locality revealed the presence of the genus Prosomys. This makes it necessary to exclude the Ruscinian age of the Cherlak fauna and assign it to the final stage of the Turolian MN 13 zone. The malacofauna retains continuity from the volcanic one. It also contains species of mainly Sino-Indian genera. The genera Tuberunio and Sibirunio, endemic to the Pliocene of Western Siberia, appear. The presence of the genus Ptychorhynchus in the malacofauna, which now lives in the south of China, and the genusOxynaia, which is now confined to Indochina, along with the thermophilic West Siberian elements, as well as the insignificant presence of Palearctic elements (31 %) indicate a significant warming of the climate during the Rytovian period.

According to V. K. Shkatova and her co-authors [1987] and Z. N. Gnibidenko [1989,1990], the Rytovskaya formation of the Cherlak section is generally inversely magnetized with low-power subzones located at different levels of the formation in the above publications. The direct polarity subzone identified by V. K. Shkatova and her co-authors (1987) is very interesting; it completes the paleomagnetic section of the Rytovskaya formation.

Taking into account that the mammalian fauna of the Novostanichnaya and Rytovskaya formations belongs to the final stage of the Turolian (upper MN 13 zone), the presence in the Novostanichnaya and Cherlak faunas of two closely related species of the genus Prosomys, a genus more archaic than Promimomys, and the geological relationship of the formations under consideration (Zykin, 1979), the only possible correlation between the magnetostratigraphic sequence of the Novostanichnaya and Rytovskaya formations is possible suite with a magnetochronological scale

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[Berggren et al., 19956; Cande and Kent, 1992] - the lower straight section zone near the village. The new Stanitsa corresponds to the upper part of subchron C3Ap1p of normal polarity, the upper reverse zone of the new volcanic section corresponds to the lower part of the reverse chron C3g. Most of the inversely magnetized Rytovskaya Formation is most likely associated with the upper Chron of the reverse C3g polarity. The direct polarity subzone that completes the magnetostratigraphic section of the Rytovskaya Formation can be interpreted as the lower part of the C3p4p crone (Tvera). In this case, the mammalian fauna of the Rytovo Formation should be placed in the upper part of the 13th Neogene mammalian zone in interpretation X. Agusti and his co-authors [Agusti et al., 2001]. The presence of similar forms of the genus Prosomys (with a more primitive form in the novostanichny complex) does not allow for a significant break between the accumulations of the Novostanichny and Rytovskaya formations.

In agreement with the above interpretation of the paleomagnetic data, a significant warming of the climate near the lower boundary of the Rytovskaya Formation should most likely be taken as global warming at the Miocene-Pliocene boundary, and, consequently, this boundary should be drawn in Western Siberia between the Novostanichnaya and Rytovskaya Formations and, accordingly, between the Novostanichny and Cherlak faunal complexes. According to V. S. Zazhigin, taking into account the history of development and the paleontological record of small mammals in the Neogene of Eurasia, it is more convenient to draw the boundary between the Miocene and Pliocene by changing the genus Prosomys to Promimomys, i.e. between the Cherlak and Isakov complexes of mammals and, accordingly, between the Rytovo and Isakov formations. The latter version is contradicted by the data on the first appearance of the genus Promimomys in Western Europe at the upper boundary of the C3p4p subchron (Tvera) and placing this boundary in the upper part of the MN 13 mammalian zone, slightly below the boundary with the MN 14 zone at the lower boundary of the C3p4p subchron (Tvera) with an age of 4.9 Ma [Ibid].

Pliocene-Quaternary boundary

One of the most controversial problems of Cenozoic stratigraphy is related to drawing the boundary between the Neogene and Quaternary systems. By decisions of the Commission on Stratigraphy of the International Union for the Study of the Quaternary Period and the Commission on Stratigraphy of the International Union of Geological Sciences in 1984, this boundary was formally drawn in the section of marine deposits of Vrica in Southern Italy under the Calabrian stage deposits with the stratotype of the global boundary point directly below the sites of the first appearance of the ostracod species Cytheropteron testudo at the top of the Olduvei direct polarity subzone. After astronomical chronology has been clarified, the age of this level is estimated at 1.81 Ma (Berggren et al., 1995a). In Russia, this border was adopted by the Moscow Time in 1991. These decisions resulted in a significant change in the Overall Stratigraphic Scale of the Quaternary system and the inclusion of a significant part of the Upper Pliocene. These decisions have led to considerable difficulties in accurately identifying the adopted boundary in various parts of the world, especially in inland areas, where many correlative features of the boundary are missing that are suitable for marine sediments. One of the main criteria for its implementation here is paleomagnetic and paleoclimatic data. The use of paleomagnetic criteria makes it possible to detect the Olduvei paleomagnetic subzone. Approximately near this border, the mammalian fauna of the middle and upper Villafranca changes.

In Western Siberia, the boundary between the Neogene and Quaternary systems is conventionally drawn within the Kochkovsky horizon by replacing the Podpusk-Lebyazhinsky mammalian complex with the Kizikhinsky one, above layers with Barnaul-type flora, and under sediments with the Kochkovsky ostracod complex (Martynov et al., 1987). The only well-characterized paleontological section in Siberia where the Olduvei subzone was found is the section on the Biteka River (a right tributary of the Ishim River) (Zykin, Zazhigin, and Kazansky, 1991; Zykin et al., 2003; Kazansky and Zykin, 1991). It is proposed as a regional stratotype of the boundary between the Neogene and Quaternary systems for North and Central Asia. Additional study of the section made it possible to clarify the details of its structure, distribution of paleontological remains, and paleomagnetic characteristics.

The Pliocene-Eopleistocene geological sequence revealed by Bitek is known as one of the main reference sections for the Upper Cenozoic of North Asia (Zykin, Zazhigin, and Prisyazhnyuk, 1987). The section's sediments of different ages contain numerous remains of large and small mammals, freshwater and terrestrial mollusks, ostracods, and plants. An outcrop on the right bank of the Bitek, 1.5 km above the mouth of the Kyzyl-Aigir, reveals one of the most complete and rich paleontological sequences of the Upper Pliocene and Eopleistocene, represented by the Mukkur and Karagash formations. Fragments of these formations accumulated at an uneven rate-

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This significantly complicates the interpretation of the paleomagnetic signal recording and the tracing of magnetozones as horizontal levels in the section.

The Mukkur formation is characterized by the Middle Villafranchian mammalian fauna, terrestrial and freshwater mollusks, and ostracods of the Mukkur complex (Kazmina, 1989). The lower part of the Karagash formation with a direct polarity contains a peculiar fauna of small mammals, among the voles of which there are only root-toothed forms. Она представлена Desmana sp., Plioscirtopoda sp., Allactaga sp., Citellus sp., Mimomys cf. pliocaenicus, M. ex gr. coelodus - pusillus, Cromeromys newtoni, Villanyia ex. gr. prologuroides, Prosiphneus sp. This fauna has no analogues in Siberia and Europe. According to the morphological characteristics of the teeth, the Karagash Mimomys and Villanyia, according to V. S. Zazhizhina (Zykin et al., 2003), are more archaic than the species of these genera in the stratotypic location of the Razdolinsky complex. Comparison with the forms of the Kizikhinsky complex does not make sense, since the previously described fauna of the typical and unique location of this complex is redeposited from several stratigraphic levels and cannot be considered a single one. The fauna of small mammals in the lower reaches of the Karagash Formation occupies an intermediate position between the Lebyazhinsky and Razdolinsky complexes in terms of the evolutionary level of microtine development. In the uppermost, inversely magnetized part of the Karagash Formation, remains of Mimomys pusillus, Villanyia prologuroides, Allophaiomys pliocaenicus, and Prolagurus pannonicus belonging to the Eopleistocene Razdolinsky complex were found. Freshwater mollusks of the Karagash formation belong to the modern Palearctic species that still live in the south of Western Siberia. Among the terrestrial mollusks in the directly magnetized part of the Karagash Formation are the genus Parmacella, which currently lives in Central Asia, and the extinct species Gastrocopta (Sinalbinula) serotina, which is close to the modern Indian species G. huttoniana.

Paleomagnetic testing of the Mukkur and Karagash formations was performed in several sections by A. Kazansky, and paleomagnetic samples were linked to the section and fauna localities by V. Zykin. The established paleomagnetic zonation in the sections of the Karagash and Mukkur formations generally corresponds to that for the Neogene - Quaternary boundary interval (Ibid., 2003). In the combined magnetostratigraphic section, three monopolar intervals are distinguished. The middle part of the Mukkur Formation is inversely magnetized (R1); the upper part of the Mukkur Formation and the lower part of the Karagash Formation form the forward polarity zone (N1); the entire overlying sequence of the Karagash Formation is inversely magnetized (R3). The reverse polarity intervals R1-R2 are fragments of the Matuyama zone. According to the above paleontological data, the range of direct polarity N1 should correspond to the Olduvei subchron. Thus, the boundary of the Neogene and Quaternary systems can be traced in the middle part of the Karagash formation and is determined by changes in the fauna of small mammals, as well as in the faunas of freshwater, terrestrial mollusks and ostracods: their distinct impoverishment is recorded at this boundary due to a cooling climate. The main biostratigraphic criterion for drawing the boundary between the Neogene and Quaternary systems in the south of Western Siberia is the appearance of the small mammal species Allophaiomys pliocaenicus directly above this boundary.

Eopleistocene stratigraphy

The Eopleistocene stratigraphy has been developed in the least detail for the south of the West Siberian Plain. In this area, the Eopleistocene occurs in places on the Upper Pliocene Irtysh and Mukkur Formations, which belong to the continental analogs of the recently identified Gelazian stage (Rio et al., 1998), and forms an almost continuous sequence of Pliocene and Eopleistocene deposits. In the south of the plain, the Kochkov horizon belongs to the Eopleistocene, which is based on the formation of the same name and includes sand-clay formations, sub-formations, bundles, and layers of different ages (Volkova et al., 2002; Martynov, 1980). They were formed in river, lake, and subaerial environments and are localized in various regions of Western Siberia. The stratigraphic divisions of the lower part of the Kochkovo horizon in the volume proposed during its separation (Arkhipov, 1971; Martynov, 1968, 1980) were derived from its composition and assigned to different stratigraphic intervals of the Pliocene (Zykin, Zazhigin, and Prisyazhnyuk, 1989a). They accumulated in sedimentary environments that reflect earlier, independent stages of geological development of the territory than the sediments assigned to its upper part. Unfortunately, the stratotype of the horizon and the formation of the same name in borehole 15 in the village is unknown. The hummocks of the Altai Territory are not characterized biostratigraphically, and the paleontological characteristics of the underlying and overlying sediments are also absent. Only the uppermost part of the formation in the stratoregion is characterized by the Kochkov (Ubinsky) ostracod complex (Kazmina, 1980). An attempt to narrow the volume of the Kochkovsky horizon to the Eopleistocene is unsuccessful, since the Kochkovsky ostracod complex is contained in the Upper Pliocene Axor layers near the village. Lebyazhye (op-

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the distribution interval of the complex and the lower horizon boundary in the stratotype may fall almost to the lower boundary of the Upper Pliocene. The uncertainty of the volume of the stratotype of the Kochkov formation and horizon, as well as its low correlation value, prevent further division of the Eopleistocene of Western Siberia on both litho - stratigraphic, bio-and climatostratigraphic bases. In this regard, it is necessary to abandon the Kochkov horizon, which is based on the stratotype of the Kochkov Formation, and replace it with a more fully paleontologically characterized subdivision, which has a clear stratigraphic position in the Eopleistocene of Western Siberia.

Among the stratigraphic divisions of the Kochkovo horizon, only stratons corresponding to the existence of the Kizikhinsky and Razdolinsky mammalian assemblages (Zazhigin, 1980) and corresponding to the Lower and Upper Eopleistocene were considered to belong to the Eopleistocene. The most clearly defined stratigraphic position in the Upper Pliocene and lower Eopleistocene is occupied by the Karagash Formation, which is widespread in the Ishim region of Northern Kazakhstan in ancient river valleys and contains the remains of small mammals that are older than the Razdolinsky ones in terms of the level of development of Mimomys and Villania species, freshwater and terrestrial mollusk complexes of the same name, and the Kochkovsky ostracod complex (Zykin, Zazhigin, and Prisyazhnyuk, 1987). In the lower part of the formation, the Olduvei subzone of direct polarity is established (Zykin et al., 2003; Kazansky and Zykin, 1991), above which the lower boundary of the Eopleistocene passes.

Eopleistocene deposits are widespread in the Pre-Altai Plain, where the Troitsky, Kizikhinsky, and Razdolinsky layers are distinguished (Adamenko, 1974; Zazhigin, 1980). Unfortunately, the stratotypes of the Troitsk and Kizikha layers do not belong to the Eopleistocene deposits of the region and contain redeposited remains of Eopleistocene fauna. Stratotype of the razdol'inskih stratievupos. Razdolye on the Alei River is the type locality of the Late Eopleistocene Razdolya (Taman) small mammal fauna (Zazhigin, 1980). According to most researchers, the Kargat and Ubinsk formations, which are poorly characterized paleontologically, belong to the Eopleistocene in Baraba.

The Eopleistocene is represented along the Ob River coastal sections and in boreholes on the Priobskaya bluff plain. According to the currently accepted MSCs stratigraphic scheme, the lower part of the Eopleistocene corresponds to the Barnaul Formation, characterized by the Kizikhin-Razdolinsky fauna of small mammals [Ibid.], and the upper part corresponds to the Yerestninsky Formation containing the Razdolinsky (Taman) complex of mammals. The Barnaul seed flora (Nikitin, 1965; Istoriya..., 1970) with thermophilic elements and a complex of freshwater mollusks with Corbicula and Borysthenia are known from the Barnaul formation. Paleomagnetic studies of pliocentennial deposits (Pospelova and Larionova, 1973) from wells 2 (Elunino village) and 3 (Kharkovo village) showed that the Barnaul Formation and the Erestninskaya Formation overlying it are mostly inversely magnetized. This magnetozone is mapped to the Matuyama orthozone of reverse polarity. In the upper part of the Barnaul deposits, at a depth of 139 - 152 m from the surface, in the 2-E well in the inversely magnetized zone, a fairly powerful subzone of direct polarity was revealed. Correlation of the Barnaul Formation with the Mukkur Formation of Northern Kazakhstan in terms of freshwater mollusk fauna makes it possible to compare the positively magnetized subzone in its upper part with the Olduvei subchron or the C2p subchron according to the U. A. Berggren et al. scale (Berggren et al., 1995a) and assign it to the Upper Pliocene. The age interval of the C2p subchron on this scale is estimated at 1.77-1.95 million years.

The Tishinskaya and Yerestninskaya seed floras (Ponomareva, 1982, 1986) and a complex of freshwater mollusks, represented by species still living in this area, are confined to the Yerestninskaya formation. As part of the Tishinsky flora, the first appearance of cold-loving plant species is noted. The Tishin seed flora and palynological data (Istoriya..., 1970) make it possible to reconstruct forest-steppe and steppe landscapes in the Early Estonian period. An increase in the number of plants of the subalpine and tundra zones in the Yerestninsk seed flora and spore-pollen spectra [Ibid.] indicates a progressive cooling. The Erestninskaya formation ends with the Malinovsky pedocomplex consisting of three hydromorphic soils, a loess horizon, and the lower part of the Evsinsky pedocomplex. Microteriofauna was found in the upper soil of the Malinovsky pedocomplex, which occupies an intermediate evolutionary position between the Razdolinsky and Vyatka complexes of small mammals. According to its stratigraphic position, it can be attributed to the end of the Matuyama crone, between the Jaramillo subchron and the Brunes-Matuyama boundary (Arkhipov et al., 1997). Thus, at present, the most complete and well-characterized paleontological section of the terminal Pliocene and Eopleistocene should be considered, in addition to the Bitekei, the section of the Priobskaya uvalistaya plain. In the stratigraphic scheme of the West Siberian Plain, instead of the Kochkovsky horizon, it is necessary to distinguish the Erestninsky horizon, which is based on the formation of the same name.

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Neo-Pleistocene stratigraphy

The most important problem for the Neo-Pleistocene stratigraphy of Western Siberia is the development of a stratigraphic sequence comparable to the oxygen isotope scale of deep-sea ocean sediments [Bassinot et al., 1994] and fully reflecting global climatic events that are associated with changes in the orbital parameters of the planet. Among the continental formations of Siberia, the loess-soil sequence (Kukla, 1977) and sediments of long-standing lakes (Prokopenko et al., 2001) are considered to contain an adequate record of these events.

Among the Neo-Pleistocene continental sediments of Western Siberia, the loess-soil sequence most fully reflects global climate changes in the time scale of orbital parameters. Its stratigraphic horizons clearly correspond to the stages of the oxygen isotope scale of oceanic precipitation and other global climate records (Dobretsov, Zykin, and Zykina, 2003); therefore, it is the only reference scale for intraregional correlations. Loess strata are widespread in the south of Western Siberia. Here its capacity reaches 120 m. It has a distinct cyclic structure - a regular alternation of loess, soil, and cryogenic horizons (Volkov and Zykina, 1991; Zykina, 1999). In recent years, considerable new material has been accumulated on the structure of the loess sequence in the south of Western Siberia. To date, more than 100 loess-soil sections have been studied and all previously published materials have been revised. In 2003, a borehole in the Lozhok quarry revealed a continuous loess-soil sequence up to analogs of the 11th oxygen isotope stage. Detailed correlation of the sections based on tracing soil horizons and pedocomplexes that have the same morphotypic features over a large area made it possible to refine the previously developed stratigraphic scheme of the subaerial sequence (Volkov and Zykina, 1991) and establish a complete loess-soil sequence in the south of Western Siberia (Dobretsov, Zykin, and Zykina, 2003) (Table 2). Chronostratigraphy The loess-soil sequence is based on paleopedological, paleomagnetic, and paleontological studies, as well as radiocarbon and thermoluminescent dating data [Arkhipov et al., 1997; Volkov and Zykina, 1991; Dobretsov, Zykin, and Zykina, 2003; Zykina, Volkov, and Dergacheva, 1981; Zykina, Volkov, and Semyonov, 2000; Zykina and Krukover, 1988 Zykina and Kim, 1989; Zander et al., 2003; Zykina, 1999; et al.].

Fossil soils are of particular importance for the correlation and dissection of sections. The main features of the structure of the loess sequence in Western Siberia include the alternation of thick loess horizons with pedocomplexes consisting of soils separated by thin loess interlayers. In the complete loess-soil sequence of Western Siberia, ten pedocomplexes are distinguished (taking into account modern soil), separated by thick loess layers. The boundary of the Brunes-Matuyama paleomagnetic inversion passes within the tenth Evsinsky pedocomplex (Zykina, Zykina, and Orlova, 2000a; Zykina, 1999).

Fossil soils that are part of pedocomplexes were formed during periods of warming in the Pleistocene, as evidenced by the age range of accumulation of modern soil, morphotypic features of Pleistocene soils, and intervals of their formation, dated by various methods. The general level of warming and moistening, as well as the duration of warm epochs, affected the intensity of pedogenesis, the structure and thickness of fossil soils. It is proposed to evaluate and compare the intensity of pedogenesis in different epochs of soil formation on the basis of a semi-quantitative characteristic on a five-point scale (Dobretsov, Zykin, Zykina, 2003). This should take into account the complexity of the organization and the degree of maturity of the profile of a particular soil type: a) differentiation of the profile into genetic horizons; b) thickness of the profile and diagnostic horizons; c) the degree of intensity of elementary soil-forming processes (humus accumulation, podzolization, lessivage, carbonate accumulation, etc.); d) microstructure of the main horizons of a particular soil type; e) the degree of densification of soil horizons.

The composition and structure of the loess layer reflect the overall intensity of atmospheric circulation. During periods of low activity of atmospheric circulation, biogenic sedimentation prevailed and soils were formed; during periods of increased atmospheric circulation, the atmosphere was saturated with dust, which, when deposited, formed loess covers. Each warm interval recorded in the subaerial Pleistocene layer as pedocomplexes differs from the previous and subsequent ones in the depth of warming and internal structure. Two or three contiguous soils of the same type, but with different subtypes or different types of soils combined in pedocomplexes, reflect the structure of each warming event. In all pedocomplexes of the loess-soil sequence, the lower soil, as a rule, retains signs of the most intense manifestation of pedogenesis and always has the greatest thickness and, consequently, the longest duration and higher thermal regime of soil profile formation. The upper soils of the pedocomplex are usually characterized by a lower thickness and

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Table 2. Stratigraphic scheme of the loess-soil sequence of the Pleistocene in the south of Western Siberia

they developed over a shorter period of time in cooler climatic conditions. Good preservation of pedocomplexes in subaerial sections indicates that there is no break in sedimentation between loess and pedocomplexes.

Detailed sequential comparison of the structure of the loess-soil sequence of the Pleistocene of Western Siberia and, especially, the structure of pedocomplexes with the structure of warm odd stages of the oxygen isotope scale (Bassinot et al., 1994), warm stages of the Baikal chronicle (Kuzmin et al., 2001; Goldberg et al., 2000; Prokopenko et al., 2001), etc. temperature and dust from ice cores from the Vostok station in Antarctica (Kotlyakov and Lorius, 2000; Petit et al., 1999) and the magnetic susceptibility of loess soil-

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In the western sequence of China (Kukla et al., 1990), it was established that the structure of fossil pedocomplexes in the Loess record of Western Siberia clearly reflects the structure of warm odd stages of continuous global sequences (see figure) consisting of close warm events separated by relatively short cold events (Dobretsov, Zykin, and Zykina, 2003). This feature makes it possible to use the structure of pedocomplexes for both intraregional and interregional and global correlations.

The clear coincidence of the time of formation of thick loess horizons with the cold stages of these records, as well as the dust enrichment of the cold intervals of Antarctic and Greenland cores [Kotlyakov and Lorius, 2000; Biscaye et al., 1997; Petit et al., 1999] indicate the formation of loess during periods of cooling and climate aridization (see figure). During glacial maxima, the dust content in the atmosphere was 30 times higher than during interglacial maxima (Broecker, 2000).

During the formation of loess covers in Western Siberia, there were cold deserts. Extensive deflation surfaces and closed deflation basins formed in the western part of the West Siberian Plain. The latter are widely distributed in the south of Western Siberia; they often contain drainless lakes. Their Aeolian origin in the arid climate is evidenced by the desert pavement, windmills, carbonate crust and desert tan on fragments and pebbles of bedrock, cracked large pebbles and small boulders at the bottom of the deflation basin of Lake Baikal. Aksor in the Pavlodar Irtysh region, which was formed during the Yermakov glaciation corresponding to the 4th marine oxygen isotope stage (Zykinidr., 2003), as well as drying wedges at the bottom of the modern lake basin. Vats developed during the Sartan glaciation in the 2nd marine oxygen isotope stage (Pulsing Lake Vats, 1982). More ancient formations are probably the drainless deflation basins of the lakes Kyzyl-Kak, Teke, Kishi-Karoy, and Ulken-Karoy. The depth of deflation basins exceeds 70 m. The Aeolian removal of material from deflationary basins occurred repeatedly during epochs of cooling and climate aridization.

In addition to sculptural forms of the Aeolian relief, accumulative relief forms, which are also genetically related to the accumulation of loess covers, are widespread in the temperate zone of Inner Asia. For example, in Western Siberia, they include the well-preserved mane topography formed during the last glaciation, and long-term large swells in the eastern part of Kulunda (Volkov, 1976). Features of the distribution and orientation of the Aeolian relief created during glaciations indicate that its formation occurred under the predominant influence of air masses of the western transport.

Recently, the continuous Baikal paleoclimatic record has become essential for the correlation of Quaternary deposits. The bottom sediments of the lake were discovered by numerous short wells and four deep well clusters (BDP-93 - 1, BDP-93 - 2; BDP-96 - 1, BDP-96 - 2; BDP-98; BDP-99) during the implementation of the international project "Baikal Drilling" (Karabanov et al., 2001; Kuzmin et al., 2001]. The sedimentary sequence has a distinct cyclic structure due to the alternation of layers of silt enriched in diatom residues and layers composed of silty clays with a very low content or complete absence of diatoms. Continuous recording of paleoclimate changes in Lake sediments. Lake Baikal with a duration of more than 10 million years is based on fluctuations in the content of diatoms and the dynamics of biogenic silica content caused by these fluctuations, as well as on fluctuations in geochemical climate indicators. Biogenic silica, which reflects the biological productivity of the lake, is a sensitive indicator of climate change: diatomaceous silts and clays were deposited during interglacial periods, while non-diatomaceous silty clays corresponded to cold glacial intervals (Bezrukova et al., 1991).

The Baikal paleoclimatic record for the last 800 thousand years, represented by the curve of changes in the content of biogenic silica in lake sediments, coincides well with the marine oxygen isotope curve (Colman et al., 1995; Prokopenko et al., 2001; Williams et al., 1997). It includes 19 stages. Peaks of biogenic silica in the Baikal record corresponding to warm periods are identified with warm odd isotope-oxygen stages. The minima are correlated with cold glacial stages and refer to even isotope-oxygen stages of the sea curve.

Elemental analysis using synchrotron radiation (RFF-SI) made it possible to obtain high-resolution geochemical records of paleoclimate signals in lake sediments and to identify several types of terrigenous paleomarkers that characterize cooling and warming of the climate [Goldberg et al., 2000]. The Sr/Ba (Rb, Cs, Ti), U/Th, Zn/Nb ratios, as well as the increased content of U, Mo, Br, Eu, Tb, Yb, and Lu are positively correlated with biogenic silica and mark warm intervals. Cold periods are characterized by an increased content of Th, Ba, Rb, Cs, La, Ce, Nd and high ratios of La(Ce, Ba)/Yb (Y, Zr).

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Correlation of the loess-soil sequence in the south of Western Siberia with global paleoclimatic events

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Spectral analysis of Baikal biogenic silica records [Colman et al., 1995; Williams et al.. 1997] and geochemical indicators of climate change [Goldberg et al., 2000] for the last 800 thousand years showed the presence of the main orbital frequencies of 100, 42, and 23-19 thousand years. The similarity of the Baikal records of climate change in terms of the number, amplitude, and shape of peaks, as well as the manifestation of orbital frequencies with the marine oxygen isotope scale [Bassinot et al., 1994] suggests that climate changes in Siberia were caused by variations in the Earth's orbital parameters and synchronously followed global climate fluctuations [Kuzmin et al., 2001].

Despite the fact that the main indicator of climate in Lake Baikal sediments is the content of diatomaceous algae flaps, which determine the alternation of diatomaceous silts and silty clays, the reason for the correlation of this parameter with global climate changes remains debatable. Since the temperature regime is not decisive for the biological productivity of diatoms, changes in their content at different intervals of the Pleistocene (Grachev et al., 2002) are suggested to be considered as the result of several factors. One of the main factors is considered to be the change in water turbidity: a sharp decrease in the turbidity of Lake Baikal waters after the melting of mountain glaciers led to a deep restructuring of the lake ecosystem and an increase in the biological productivity of diatoms (Bezrukova et al., 1991). The presence of nutrients such as dissolved silica and phosphorus in water is essential for the development of diatom flora (Gavshin, Bobrov, and Khlystov, 2001; Lisitsyn, 1966). Changes in the rate of ingestion of biogenic elements Si, P are associated with a sharp decrease in the rate of chemical weathering with a decrease in the average annual temperature by 6°C (Grachev et al., 2002). Another reason for the absence of dissolved silica entering the lake and the periodic disappearance of diatoms is the cessation of the flow of lowland rivers into the lake due to a decrease in the intensity of atmospheric moisture loss during climate aridization during the glacial maximum (Goldberg et al., 2005). One more factor should be added to these factors that influenced the decrease in the diatom content in the lake (Dobretsov et al., 2006). It is associated with a significant increase in dust in the atmosphere during glacial epochs (Broecker, 2000), which deposited on the earth's surface and formed loess covers. Dust contained in significant amounts in the atmosphere reduced its transparency, increased its turbidity when entering water, and significantly affected sedimentation. When falling on ice, the duration of which during glaciations could have increased by two months (Shimaraev, Granin, and Kuimova, 1995) or significantly longer, the dust created a screen for light penetration. Currently, mass blooming of diatoms in Lake Baikal occurs in spring under ice [Verkhozina, Kozhova, and Kusner, 1997], so an increase in dust in the atmosphere leads to a weakening of photosynthesis and a significant reduction of diatoms during aridization and cooling of the climate. The aridization of the climate during glaciations in the lake catchment area is indicated by the presence of loess covers in the Baikal region and the presence of windmills in the Selenga terraces (Bazarov, 1986), which indicate active Aeolian activity and a temporary cessation of runoff in this valley. Thus, the Baikal climate record reflects not only global changes in the thermal regime, but also significant changes in climate aridization that correlate with temperature.

Comparison of the loess-soil sequence of Western Siberia with the continuous Baikal record of biogenic silicon from the BDP-96 - 2 well sediments (see figure) covering the Brunes chrono age interval (0 - 780 Ka). years) [Kuzmin et al., 2001; Prokopenko et al., 2001], shows that the number of major peaks and minima in the Baikal record coincides with the number of major epochs of soil formation and forest accumulation. Pedocomplexes correspond to grouped BiSi peaks synchronized with odd stages of the oxygen isotope scale. This suggests that both sequences reflect the same number of major cold snaps and warming events, and that in the middle latitudes of Siberia, climate changes occurred synchronously. At the same time, a comparison of the Baikal record with the loess-soil sequence revealed that the loess record more fully represents climate changes in the late Pleistocene. In the Loess-soil sequence of Siberia, two Iskitim soils are clearly traced, which are less developed in comparison with the modern one and correspond to the 3rd isotope-oxygen stage. In the Baikal BiSi record, this time is represented by a single very weak peak (Kuzmin et al., 2001; Prokopenko et al., 2001).

The Loess record of Western Siberia and the temperature record in the ice core at the Vostok station in Antarctica coincide particularly well [Petit et al., 1999]. In Western Siberia, as in Antarctica, the strongest and longest warming events correspond to the initial substages of odd stages; later warm events of odd stages are more weakly expressed in both records.

Coincidence of the loess-soil sequence of Western Siberia with continuous records

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Bassinot et al., 1994; Goldberg et al., 2000; Kukla et al., 1990; Petit et al., 1999], in which spectral analysis revealed cycles of approximately 20 -, 40 -, and 100-millennial periodicity due to changes in the planet's orbital parameters, indicates the presence of a similar periodicity in the Loess layer (Dobretsov, Zykin, and Zykina, 2003). The Brunes chronon is clearly dominated by a 100-thousand-year cycle, which causes the alternation of thick loess layers that correspond to even stages of the isotope-oxygen curve and pedocomplexes that correspond to odd stages. During most of the warm epochs that belong to odd marine isotope stages, sedimentation was controlled by a 20-thousand-year orbital cycle. It is expressed in pedocomplexes in the alternation of fossil soils and thin loess interlayers. The 20-thousand-year orbital cycle was not reflected in the cold epochs of the Middle Pleistocene, during which thick loess strata were formed in Western Siberia, but it was clearly manifested in the Late Pleistocene loess record, causing the alternation of six underdeveloped soils. In the previous time, this cycle apparently had a smaller amplitude and was not reflected in the Loess record of the middle latitudes of Siberia.

Conclusion

Thus, the integrated use of lithological-genetic, paleogeographic, paleoclimatic, paleomagnetic, and various biostratigraphic methods with a fairly complete and detailed study of specific sections and strict justification for the allocation of local stratons made it possible to make significant adjustments to the understanding of the structure of the sedimentary sequence in the south of Western Siberia, significantly clarify the stratigraphic sequence of sedimentation in this vast region, and identify many geological, biotic and climatic events of global and regional character. The data obtained show a clear synchronism and general course of climate and environmental changes in the Late Cenozoic of Western Siberia with global climate events and indicate a unified mechanism of climate change on the planet.

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The article was submitted to the Editorial Board on 23.11.06.

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