E. B. Karabanov, A. A. Prokopenko, M. I. Kuz'min, D. F. Williams, A. N. Gvozdkov, and E. V. Kerber
Keywords: Siberian chronostratigraphic scheme, glacials, interglacials, Brunhes Chron, paleoclimate records, oxygen isotope records, correlation, Lake Baikal
Pages: 48-63 Subsection: BAIKAL CLIMATIC RECORD
he article presents a new Lake Baikal paleoclimate record of biogenic silica for the Brunhes Chron (from 780 ka ago to the present). Correlation of the Lake Baikal record with the marine oxygen isotope record shows that climatic changes of Central Eurasia are not specific but follow the pattern of global climate fluctuations of the Northern Hemisphere caused by orbital forcing. Specific features of continental climatic changes (glaciations during substages 5d, 7d, 9d, and 15bcd) were also found in the Baikal record. Correlation of paleoclimate record of biogenic silica from Baikal bottom sediments with Siberian stratigraphic scheme was made for the Brunhes Chron. The paleoclimatic events of Lake Baikal are well identified with marine oxygen isotope stages and correlate well with climatic events of Siberian stratigraphic schemes for the Late Pleistocene but do not correlate for the Middle and Early Pleistocene. There are 10 warm interglacial and 9 cold glacial periods during the Brunhes Chron of Lake Baikal, which agree with marine records but disagree with the Siberian stratigraphic scheme having only 7 glacial and 8 interglacial periods within the Brunhes. This disagreement is probably related to the incomplete nature of terrestrial outcrop sections of Siberia. The new Lake Baikal record may provide an important chronostratigraphic base for Central Asia.
E. L. Goldberg, M. A. Fedorin, M. A. Grachev, K. V. Zolotarev, and O. M. Khlystov
Keywords: Pleistocene, bottom sediments, paleoclimate, biogenic and terrigenous paleoindicators, tracer elements, glaciation, Lake Baikal
Pages: 76-86 Subsection: BAIKAL CLIMATIC RECORD
An X-ray fluorescent analysis with synchrotron radiation (SR-XFA) and neutron-activation analysis (INAA) were used to interpret high-resolution geochemical records of paleoclimate signals in bottom sediments of Lake Baikal. Concentrations of some elements and their ratios respond to climate change and thus mark glacial and interglacial stages. Sr/Ba, Sr/Rb, Sr/Cs, Sr/Ti, U/Th, Zn/Nb, U, Mo, Br, Eu, Tb, and Yb show positive correlations with the content of biogenic silica (Sibi), which is high in the periods of interglacials and low in those of glacials, whereas Ba, Rb, Cs, Th, La, Ce, Nd, and La (Ce, Ba)/Yb (Y, Zr) anticorrelate with Sibi, and increased concentrations of these elements mark glacial stages. The two series of geochemical signals, along with biogenic silica, reflect climate fluctuations from glacials to interglacials through the past 780 ka.
M. A. Krainov, V. A. Kravchinskii, J. A. Peck, H. Sakai, J. W. King, and M. I. Kuz'min
Keywords: Paleomagnetism, paleoclimate, rock magnetism, magnetic susceptibility, magnetostratigraphic scale, Milankovitch cycles, Baikal
Pages: 87-97 Subsection: BAIKAL CLIMATIC RECORD
Two boreholes on the Akademichesky Ridge, 100 and 200 m deep (BDP-96-1 and BDP-96-2), were drilled and cored continuously as part of the Baikal Drilling Project. Results of low-frequency magnetic susceptibility measurements of the two cores were correlated with the SPECMAP oceanic oxygen isotope curve, and a composite section was compiled. The SPECMAP curve and the magnetic susceptibility of the BDP-96 cores showed a good fit. Frequency analysis of time variations in magnetic susceptibility showed a periodicity of the paleoclimate signal with intervals of 23, 35, 41, 52, 68, 85, 106, and 164 ka. The periods of 23, 41, 52, and 106 ka correspond to cycles of precession, inclination of the Earth's axis, an eccentricity harmonic overlapped with inclination, and the Earth's orbit eccentricity itself, respectively. The periods of 35, 68, and 164 ka, distinguished for the first time in magnetic susceptibility studies but noted earlier in biogenic silica analysis, reflect different eccentricity harmonics, and the period of 68 ka bears an effect of precession. The period of 85 ka has never been revealed before in the climate record and is most likely related to regional periodicity rather than to any astronomic cycles.
G. K. Khursevich, E. B. Karabanov, A. A. Prokopenko, D. F. Williams, M. I. Kuz'min, S. A. Fedenya, A. N. Gvozdkov, and E. V. Kerber
Keywords: Diatom zones, stratigraphy, correlation, species extinction, species formation, Lake Baikal
Pages: 108-129 Subsection: BAIKAL CLIMATIC RECORD
The Baikal bottom sediments (borehole BDP-96-2) are stratigraphically characterized in detail (with a 500 year resolution) within the Brunhes Chron. The sediment section 35 m thick shows a distribution of diatoms (25 species and varieties), sponge spicules, and golden-algae cysts. Thirty-one local diatom zones are recognized in the section, providing a detailed stratigraphic division of the Baikal sediments. The distribution of diatom frustules and the diatom zones are correlated with the marine isotope stratigraphy. Climate played an important role in the formation of species of plankton diatoms in the lake. More than 21 new species of diatoms appear and then disappear in the section. Diatom species extinguished when glaciations began, and new species appeared during interglaciations. This suggests that the evolution of plankton diatoms in Baikal is under climatic control.
Spicules have been investigated in Late Pliocene core samples from the borehole BDP-96-1. The samples have been dated paleomagnetically. A total of 42 spicule types have been discovered, of which 15 are found in modern Baikal sponges and 27 are not. Analysis of the range of species and quantitative indices of the spicules in bottom sediments has revealed three stages of sponge-fauna development: 3.1-2.9, 2.9-2.5, and 2.5-2.1 Ma BP. The sponge fauna of the first stage is indicative of warm-water conditions. Most of thermophilic and fossil species disappeared from the second stage, which points to a dramatic cooling. At the third stage, regeneration of the sponge fauna began. However, it did not reach the efflorescence of the first stage. The results are in agreement with the palynological and diatom analysis of the core samples from the investigated depth range.
M. L. Myachin and L. A. Pevzner
Keywords: Wavelet analysis, logging data, cyclicity (periodicity), evolution processes, climatic changes
Pages: 138-145 Subsection: BAIKAL CLIMATIC RECORD
An attempt is made to study the cyclicity (periodicity) of the Earth's evolution processes, which may be expressed in the structure and state of geological section. A particular purpose of this work was to reveal periodical changes in the environment and climate of Central Asia by analyzing the logs obtained from the boreholes drilled in the Baikal bottom sediments (International Baikal Drilling Project). A basic method for revealing the cyclic structure of the signal was the body of wavelet analysis. The obtained analytical data correspond to the known periods recognized by M. Milankovitch and suggest that the Central Asian climate varied to show cycles of 13-14, 16-27, 35-57, and 75-120 ka.
E. P. Solotchina, A. A. Prokopenko, M. I. Kuz'min, A. N. Vasilevskii, and S. G. Shul'zhenko
Keywords: X-ray diffraction, modeling, illite-smectites, paleoclimate reconstruction, Lake Baikal
Pages: 146-156 Subsection: CLAY MINERALS IN BAIKAL SEDIMENTS
By comparing the compositions of glacial and interglacial intervals of the Late Pliocene, Pleistocene, and Holocene from different parts of Lake Baikal, we demonstrate the use of the Baikal clay mineral associations as indicators of past changes of environment and climate. The methodical part of this work discusses the optimal sample preparation techniques and develops the previously suggested method for structural modeling of X-ray diffraction patterns as the most suitable for studying the Baikal sediments. The clay mineral associations in the Selenga delta area and at the Akademichesky Ridge are very similar, thus indicating a minor influence of local sediment sources on their formation. The similarities revealed by this comparison indicate uniformity of the Baikal catchment basin in terms of the processes of erosion, weathering, and supply of sediments. Despite the conditions of continuous hemipelagic sedimentation at the sites where deep drilling took place, both drill cores reveal a strong relation between the composition of clay mineral associations and paleoclimatic conditions. Intervals if glacial sediments during both the Late Pleistocene and the Late Pliocene are similar and are characterized by dramatic enrichment in well-crystallized mica (muscovite) and plagioclase, indicating intensification of physical weathering under cold climatic conditions. Interglacial intervals are enriched in fine illite, which suggests that it is a secondary mineral, the product of chemical weathering. In addition, the content of smectite layers in mixe layer illite-smectite increases during interglacials, which is also likely to imply a warmer and more humid climate. The lower interval of the BDP-96 core with the age over 4.5 Ma is characterized by an anomalous composition: high content of illite-smectite with a high concentration of smectite component, the presence of chlorite-smectite, and low contents of illite and muscovite. This specific mineral association has formed under climatic conditions much warmer than at present.
S. A. Kashik, T. K. Lomonosova, and T. S. Fileva
Keywords: Lithology, bottom sediments, clay minerals, mineralization, physicochemical modeling, Lake Baikal
Pages: 164-174 Subsection: CLAY MINERALS IN BAIKAL SEDIMENTS
The paper treats over the results of lithological studies of the core dredged from the borehole which was drilled under a 354 m thick water layer of Lake Baikal. The structural and geochemical specialization of clay minerals in bottom sediments of Lake Baikal has been established for the first time to a depth of more than 100 m. The quantitative composition of mineral phases of a thin-pelitic fraction is calculated with the help of computing procedures "Simplex". It is shown that smectites are represented by beidellite, montmorillonite, and, to a smaller degree, nontronite. They actually reflect the range of mineral varieties of this group, which is characteristic for allochthonous and autochthonous genesis. Terrigene smectites in sediments are indicative of semi-arid and semi-humid climate in the Miocene and, to a smaller degree, in the Pliocene. The acme of diatoms and maximum abundances of smectites may be linked with the thawing of glaciers and ices whose regelation waters are able to transport terrigene smectite and carry a great amount of dissolved silica necessary for building a silica framework of this variety of phytoplankton. Also, the reserve of smectites considerably grew during authigenic mineralization. The proof is examination of samples on SEM.
M. A. Fedorin, E. L. Gol'dberg, V. A. Bobrov, O. M. Khlystov, and M. A. Grachev
Keywords: Baikal mud, uranium, thorium, Brunhes, XRF-SR, INAA, ICP-MS
Pages: 186-193 Subsection: DATING METHODS
The paper presents a new method of U and Th determination in bottom sediments implying synchrotron radiation with monochromatic beams at different energies, registration, and iterative joint processing of the resultant XRF (X-ray fluorescent) spectra series. The validity of the new method was proved by comparison of U and Th determinations by XRF-SR in different sediment samples with earlier INAA and ICP-MS results for the same samples. Profiles of U and Th were measured at the sampling rate of 2 ka in a drilling core (BDP-96-2) of bottom sediments from Lake Baikal deposited 40 to 780 ka BP. Oscillations of U contents and U/Th ratios record global climate change throughout the Brunhes epoch (780 ka BP), and the response of these "warm" proxies is similar to that observed earlier in shorter cores spanning the last two interglacials (220
I. V. Sandimirov, A. A. Kosov, and T. A. Vladimirova
Keywords: Pleistocene, paleoclimate, glaciations, Th-U dates, Lake Baikal
Pages: 194-205 Subsection: DATING METHODS
We propose a method for dating Baikal deep-water sediments from the ratios of radioactive isotopes of Th and U in various fractions of the authigenic part of the sediments. We have determined the Th-U age of six horizons of the borehole BDP-96-2 and the average parameters of gravitational consolidation of the sediments. The extrapolated Th-U ages show a good correlation with paleomagnetic data throughout the core of BDP-96-2.
