THE IGETEY REFERENCE SECTION OF MULTILAYER ARCHEOLOGICAL SITE (MIDDLE PLEISTOCENE – HOLOCENE, CIS-BAIKAL): STRATIGRAPHY, GEOCHRONOLOGY, AND SEDIMENTATION ENVIRONMENT
A.A. Shchetnikov1,2*, A.Yu. Kazansky1,3, N.E. Berdnikova4, I.M. Berdnikov4, I.A. Filinov1,2, V.V. Ivanova5, G.A. Danukalova6, E.M. Osipova6, F.I. Khenzykhenova7, O.D. Namzalova7, D.G. Malikov8
1Institute of the Earth's Crust, SB RAS, Irkutsk, Russia
2Vinogradov Institute of Geochemistry, SB RAS, Irkutsk, Russia
3Geological Institute, RAS, Moscow, Russia
4Irkutsk State University, Irkutsk, Russia
5Institute of Precambrian Geology and Geochronology, RAS, St. Petersburg, Russia
6Institute of Geology, Ufa Federal Research Centre RAS, Ufa, Russia
7Geological Institute SB RAS, Ulan-Ude, Russia
8Sobolev Institute of Geology and Mineralogy, SB RAS, Novosibirsk, Russia
Keywords: Igetey reference section, Cis-Baikal, Middle–Upper Pleistocene, IR–OSL dating, paleo- and petromagnetic analysis, malacofauna, environmental changes.
Abstract
The paper presents the results of comprehensive study of the section of the multilayered archeological Igetey section (Lower–Upper Paleolithic, Cisbaikalia). For the first time, a geochronological characteristics of the full thickness of the section was obtained based on IR–OSL dating. The sedimentary deposits found at the Igetey geoarcheological section were found to be between 155,000 and 160,000 years old. The stratigraphic sequence of sediments of all isotopic stages of the Upper Pleistocene and Holocene (MIS 5–1), as well as stage 6 of the Middle Pleistocene, was characterized. In terms of lithologic-facial conditions, the Igetey section is represented by a complexly constructed heterogeneous formation of the slope (cryogenic-deluvial-proluvial) and subaerial series with eight horizons with pedogenesis, including modern soil, and seven cultural layers. The upper part of the section (to a depth of 12 meters) reveals the structure of a colluvial fan with aeolian sediments and paleosols. The Middle Pleistocene cover sediments of the coalescing fan are exposed below. This part of the section is represented by a loess-soil sequence, in which a substantial pedocomplex of five paleosols is distinguished, dating to the second half of MIS 6 (135–160 ky BP) and probably recording the early stage of the last Pleistocene interglacial. All paleosols, according to their petromagnetic properties, have a "Siberian" formation mechanism and are characterized by the presence of cryogenic disturbances. Data obtained from studying the species and quantitative diversity of terrestrial and freshwater mollusks made it possible to trace changes in the structure of biotopes and reconstruct the paleoecological conditions in the area of the Igetey section from the Middle to Late Pleistocene. During the formation of the Middle Pleistocene deposits (the second half of MIS 6), the climate was generally moderately cool, with open space biotopes predominating, which were located in the river valley, and at the same time, there were several intervals of climate warming. The enhancement of conditions is recorded during the formation of layers 17, 14, 11, and 9. The climate was moderately warm and humid, and the biotopes of open spaces were supplemented by intermediate ones. The results from the Early Late Pleistocene malacocomplex (MIS 5) indicate a moderate climate in both temperature and humidity (layer 7), followed by a period of cooling (layer 6). During this time, open-space biotopes predominated.
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