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2001 year, number 1-2
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M. I. Kuz'min, E. B. Karabanov, T. Kawai, D. Williams, V. A. Bychinskii, E. V. Kerber, V. A. Kravchinskii, E. V. Bezrukova, A. A. Prokopenko, V. F. Geletii, G. V. Kalmychkov, A. V. Goreglyad, V. S. Antipin, M. Yu. Khomutova, N. M. Soshina, E. V. Ivanov, G. K. Khursevich, L. L. Tkachenko, E. P. Solotchina, N. Ioshida, and A. N. Gvozdkov
Keywords: Baikal Drilling Project, gas hydrates, paleoclimate record, diatom abundance, biogenic silica
Pages: 8-34
Abstract >>
The paper presents the results of ten-years deep drilling on Baikal (joint Russian-American-Japanese Baikal Drilling Project). During the project run, five sets of boreholes were drilled in various geomorphic structures of the lake. Avalanche sedimentation has been established in deep basins of the rift lake. The sedimentation provides a great amount of plant producing methane in the sedimentary series. The physicochemical conditions at the bottom of deep basins favor formation of gas hydrates, which have been first found in the fresh-water lake.
A precise age control of the Baikal sedimentary sections based on detailed paleomagnetic data as well as their continuity and a considerable length allowed us to obtain a unique paleoclimatic record, which may provide a reference model for Asia and the whole continental Northern Hemisphere. Boreholes on the Akademichesky Ridge yield a record of more than 10 Ma with the age resolution of 500 to 250 years. The boreholes on the Bugul'deika saddle spanned a section of 600 ka with the age resolution of 25 to 100 years.
Distribution of diatoms and, hence, of biogenic silica, palynological data, and data on chemistry and mineralogy of sediments give insight into the paleoclimates of the Baikal region. The obtained continental climate record shows a perfect correlation with the oceanic oxygen isotope stratigraphy. At the same time, climate response in the continental cores is better pronounced. The Baikal paleoclimate record bears well-expressed evidence of cooling that occurred about 2.5-2.8 Ma ago, when ice sheets appeared in various regions of the Northern Hemisphere. Climate variations over the past 5 Ma are considered in detail.
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D. F. Williams, E. B. Karabanov, A. A. Prokopenko, M. I. Kuz'min, G. K. Khursevich, A. N. Gvozdkov, E. V. Bezrukova, and E. P. Solotchina
Keywords: Climate markers, biogenic silica, diatoms, climate and tectonic changes, Lake Baikal, Siberia
Pages: 35-47
Abstract >>
The decade of scientific drilling and multidisciplinary studies of lacustrine sedimentary sequences on Lake Baikal has contributed greatly to expansion of our knowledge on the Asian continent response to global climate and regional tectonic changes. This paper is an effort to sum up the available results and to outline the issues of further investigations.
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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
Abstract >>
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.
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A. A. Prokopenko, E. B. Karabanov, M. I. Kuz'min, and D. F. Williams
Keywords: Paleoclimate modeling, regional mechanism of glaciation, sediment record, Lake Baikal, Siberia
Pages: 64-75
Abstract >>
We discuss stratigraphic and correlational age modeling of the Baikal sediment record and summarize studies of paleoclimate records in cores from various regions of Lake Baikal. The available paleoclimate reconstructions attest to an abrupt strong Early Wurm glaciation in the Baikal region at the oxygen isotope substage 5d, (117-105 ka BP). This confirms the existence of an "additional" glaciation predicted for Siberia from paleoclimate modeling and suggests a regional mechanism responsible for the intensity of this glaciation, which was better pronounced in Siberia than elsewhere in the Northern Hemisphere.
The available data on the Early Zyrjanian glaciation in Siberia provide an insight into the space-time dynamics of the origin of the Early Wurm glaciation and can account for the discrepancy between a considerable (about 40%) increase in global ice volume at the substage 5d and the lack of physical evidence for glaciation from other regions of the Northern Hemisphere. Catastrophic events of the 5e/5d transition revealed in the Baikal sediment record and in other Siberian data indicate a significant role of Siberia in climate-forming processes in the Northern Hemisphere.
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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
Abstract >>
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.
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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
Abstract >>
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.
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E. V. Bezrukova and P. P. Letunova
Keywords: Bottom sediments, spore-and-pollen assemblages, Pleistocene, vegetation and climatic changes, Lake Baikal, East Siberia
Pages: 98-107
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Two boreholes, BDP-96-1 (200 m thick) and BDP-96-2 (100 m thick), drilled at the top of the underwater Akademichesky Ridge at 53o41'48''N and 108o21'06'', gave two parallel cores which were dated paleomagnetically. The correlation of the paleomagnetic data with the global magnetic scale has shown the age of the sediments exposed at a depth of 200 m to be 5 Ma. The average sedimentation rate was constant, about 4 cm/ka. Earlier palynological studies of core samples from BDP-96-1 were performed at 2 m intervals, which corresponds to the period of ~45-50 ka. In this paper, we present results of a detailed palynological analysis of the upper 30 m of the core performed at 20 cm intervals (4-5 ka). The age of the investigated core from BDP-96-1 covers most of the Brunhes epoch. Taking into account the lost upper 630 cm, it matches the time range from 170 to 780 ka BP. Palynological analysis of the sediments from the range under discussion revealed 13 epochs in the development of the regional flora structure: seven epochs of predominance of forest plant formations and six epochs of its significant degradation. The epochs are correlated with the stages of changes in the volume of global ice, recorded in the marine oxygen isotope scale. It is difficult to determine the extents of the coolings, because spores and pollen are scarce in the sediments of these epochs. However, it is apparent that forests did not disappear from East Siberia during the coolings. All main arboreal species now growing there persisted during Pleistocene glaciations. The structure of the vegetative cover underwent profound changes. The areas occupied by forests decreased. Larch and spruce north-taiga forests were predominant under the humid cold conditions of the beginning of interglacials and the end of glaciations; they were then replaced by fir and cedar pine forests. Larch-pine and cedar pine middle-taiga forests expanded under the moderately warm and relatively dry climate of the mid-interglacials. Obviously, this was accompanied by a wide spread of steppe vegetation. A comparison of the frequency and habit of changes in vegetation type in the study region 170-780 ka BP with those in various regions of the Northern Hemisphere demonstrates that the East Siberian vegetation responded to global climatic changes synchronously with the vegetations of other regions.
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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
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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.
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E. V. Weinberg
Keywords: Sponge fauna, spicule analysis, Late Pliocene, Lake Baikal
Pages: 130-137
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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.
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M. L. Myachin and L. A. Pevzner
Keywords: Wavelet analysis, logging data, cyclicity (periodicity), evolution processes, climatic changes
Pages: 138-145
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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.
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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
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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.
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J. Muller, E. G. Vologina, and M. Sturm
Keywords: Clay minerals, recent sedimentation, detrital sedimentation, source rocks, Lake Baikal
Pages: 157-163
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Analyses of clay minerals have been performed on recent and ancient (age  900 years) sediments of the west-east trending Zavorotnyi transect in the North Basin of Lake Baikal (southeastern Siberia). The aim was to study clay minerals to identify the characteristics of the eastern and western sediments and to relate them to catchment areas or to sedimentation mechanisms. Apart from illite, which is the most abundant mineral along the transect, the clay mineralogy changes distinctly between the eastern and western sediments. The western clayey sediments are characterized by high chlorite contents, low smectite and kaolinite contents, and a general good crystallinity of all clay minerals. The eastern clayey sediments have lower chlorite contents, higher smectite and kaolinite contents, and poorer crystallinity of the clay minerals. We suggest that differences in the geological background and morphology of the catchment areas lead to these differences between the eastern and western surface elements as a result of different weathering and transport mechanisms prior to sedimentation. The smectite content and illite-chlorite ratio are possible indicators for differentiating between the western and eastern predominant sediments. From this interpretation it follows that western catchment areas supplied the turbidites accumulated in the center of the Zavorotnyi transect. The great variability in distribution of clay minerals over a few hundred years, most pronounced in the smectite content and illite-chlorite ratio, indicates significant changes in the factors controlling sedimentation in the North Basin. This must be taken into account when using the distribution of clay minerals in Baikal sediments for paleoreconstructions.
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S. A. Kashik, T. K. Lomonosova, and T. S. Fileva
Keywords: Lithology, bottom sediments, clay minerals, mineralization, physicochemical modeling, Lake Baikal
Pages: 164-174
Abstract >>
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.
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M. Horie, H. Sakai, K. Kashiwaya, T. Nakamura, and T. Kawai
Keywords: Granulometry, drilling, 14C dating, age model, Lake Baikal
Pages: 175-185
Abstract >>
Rock-magnetic and granulometric studies were conducted on the BDP-93 cores (100 m in length) obtained from the Bugul'deika saddle of Lake Baikal, southeastern Siberia. The remanent magnetization of the cores shows dominant positive inclination, indicating that the cores are included in Brunhes normal chron ( 780 ka BP). Some geomagnetic excursions were found in both cores. With the age scale referred to 14C dates and regeression, they are estimated to be 100 and 120 ka BP (Blake event), 310 and 340 ka BP (Calabrian ridge, event 1). These geomagnetic events possibly include double excursions. Comparison of magnetic properties with the content of diatoms and biogenic SiO 2 shows a low concentration of magnetic minerals during interglacial periods and a high concentration during glacial periods. However, this relation is obscure at the lower 60 meters of the core. Rock-magnetic and other parameters suggest a change in sedimentation environment at a depth of 40 m, which may be related to a shift of the sedimentary source. These results suggest that the sedimentation environment of the Bugul'deika saddle was influenced by the local sedimentation conditions.
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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
Abstract >>
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
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I. V. Sandimirov, A. A. Kosov, and T. A. Vladimirova
Keywords: Pleistocene, paleoclimate, glaciations, Th-U dates, Lake Baikal
Pages: 194-205
Abstract >>
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.
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Y. Tani, K. Yoshi, N. Ito, F. Nara, M. Soma, A. Tanaka, Y. Soma, M. Yonada, M. Hirota, and Y. Shibata
Keywords: Photosynthetic pigments, biological indicators, sediment, biogenic silica, perylene, Southern basin, Lake Baikal
Pages: 206-212
Abstract >>
Depth profiles of carotenoids, chlorophyll derivates, and other biogenic indicators, such as biogenic silica (BGS), total organic carbon (TOC), total organic nitrogen (TON), and perylene, were measured in 14C-dated sediments ( 2m thick) sampled from the Southern basin of Lake Baikal. The photosynthetic pigments, BGS, and TOC (TON) accumulated in the upper part (80 cm) of the core (dated at 12-13 ka BP), whereas biogenic perylene occurs in its lower part (below 80 cm). Biogenic silica in the upper part shows a negative correlation with total carotenoids and no significant positive correlation with TOC and total chlorophyll a. This indicates that high contents of BGS providing oxidizing conditions in the lake stimulate aerobic decomposition of organic compounds in the water and in the surface sediments. The high concentrations of perylene in the lower part of the core against the background of the low lake productivity suggest specific processes of sedimentation in the past.
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Y. Soma, M. Soma, Y. Tani, A. Tanaka, and T. Kawai
Keywords: Photosynthetic pigments, chlorophyll, carotenoids, organic carbon, biogenic silica, bottom sediments, Lake Baikal
Pages: 213-219
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We have investigated the distribution of photosynthetic pigments (chlorophyll and carotenoids), total organic carbon (TOC), and biogenic silica in the surface sediments throughout Lake Baikal and suggested factors controlling this distribution.
The concentrations of photosynthetic pigments preserved in the surface sediments of Lake Baikal have been established to be high in the Southern basin and minimum in the Central basin, including the Akademichesky Ridge, while TOC is distributed rather evenly, and the contents of biogenic silica are higher in the Central and Northern basins. The oxidizing conditions in the surface sediments and the low sedimentation rate in the Akademichesky Ridge caused intense decomposition of pigments. The large inflow of the Selenga River significantly disturbs sedimentation in the Southern basin and thus causes uneven spatial distribution of pigments. Carotenoids found in the Southern basin are also diverse, thus suggesting their origin from different classes of algae.
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I. S. Andreeva, E. I. Ryabchikova, N. I. Pechurkina, B. N. Zaitsev, V. F. Geletii, E. D. Korobushkina, T. P. Vinogradova, T. Torok, J. Hunter-Cevera, and V. E. Repin
Keywords: Baikal Rift Zone, drilling, bottom sediments, ancient microorganisms, cells ultrastructure
Pages: 220-230
Abstract >>
Microorganisms of the Baikal Rift are of peculiar interest owing to their isolated evolution and the ancient origin of Lake Baikal. Samples of rocks sedimented at various stages of the Baikal Rift development have been obtained by drilling. Based on microbiological examination of bottom samples from the Baikal basin, a collection of more than 2200 microbial isolates was made. They include the genera Micrococcus, Staphylococcus, Bacillus, and Nocardia; numerous nonsporogenous cocci and bacilli with well-pronounced capsules; fast-moving Gram-negative rods, assigned to pseudomonads; sessile Gram-negative cells, actinomycetes, and yeast. The eukaryotes of the ground samples also contain mold fungi.
The morphological features were studied by light microscopy of colored microbial cells and using scanning and transmission microscopes.
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V. E. Repin, T. Torok, S. Kh. Degtyarev, M. Abdurashitov, L. I. Puchkova, I. S. Andreeva, N. I. Pechurkina, A. A. Gus'kov, J. Hunter-Cevera, and V. F. Geletii
Keywords: Sedimentary rocks, thermal springs, Lake Baikal, restriction endonucleases
Pages: 235-240
Abstract >>
Microorganisms isolated from sediments of Lake Baikal and nearby thermal springs (Zmeinyi and Goryachenskii) have been tested as producers of restriction enzymes. The production has been detected in 20% of the investigated strains. Three strains are of particular practical interest. Two of them are thermophilic producers of novel enzymes, and the restriction endonuclease from the third one demonstrates an unusual sensitivity to dam methylation of the recognition site.
It has been shown that the content of viable microorganisms varied throughout the sediments.
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T. E. Afonina and E. B. Karabanov
Keywords: Bottom sediments, biomarkers, n-alkanes, organic matter, humic acids, Lake Baikal
Pages: 241-253
Abstract >>
We present new data on the distribution and composition of n-alkanes (biomarkers) and humic acids in the Holocene and Pleistocene bottom sediments of Northern Baikal accumulated under different sedimentation and paleoclimatic conditions. These data show significant amounts of allochthonous organic matter (OM) in the Holocene sediments of various sedimentation settings, which was supplied mainly with suspension flows. During glaciations, accumulation of both allochthonous and autochthonous OM was considerably reduced. In these periods, when no diatoms existed, autochthonous OM was produced from cyanobacteria and blue-green algae.
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E. G. Vologina and V. L. Potemkin
Keywords: Eolian transport, bottom deposits, paleoclimate, sedimentation, granulometry
Pages: 254-257
Abstract >>
Results of study of winter eolian transport in the region of the Akademichesky Ridge of Lake Baikal are presented, based on data of granulometric and mineralogical analyses of the suspended matter of snow cover accumulated for the period January-March 1998. The wind velocities necessary for transportation of quartz grains of different sizes from the Baikal Ridge (western shore of Baikal) to the study region are calculated. The conclusion is drawn that winter eolian transport plays an important role in the supply of clastogene material to the region of the Akademichesky Ridge.
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G. P. Koroleva, A. A. Kosov, V. F. Geletii, and E. G. Vologina
Keywords: Eolian transport, geochemistry, anomalous elements, background elements, sources of matter
Pages: 258-266
Abstract >>
Results of geochemical study of suspended matter (SM) from the snow cover of the Akademichesky Ridge of Lake Baikal are presented. Geochemical data are processed by methods of the mathematical theory of pattern recognition on the basis of distance functions. The conclusion is drawn that the eolian material of the Akademichesky Ridge was transported mainly from the western shore of Lake Baikal. Solution of the optimization problem has shown that 45% of the studied SM was transported from the western shore, 15% from the eastern one, and 40% from far regions.
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V. A. Bobrov, T. V. Khodzher, L. Z. Granina, M. S. Mel'gunov, Yu. P. Kolmogorov, and A. L. Poslovin
Keywords: Rare-earth elements, eolian particles, river suspensions, bottom sediments, paleoclimate, neutron-activation analysis, Lake Baikal
Pages: 267-277
Abstract >>
Neutron-activation analysis with the use of the X-ray fluorescence method permitted us to determine a number of rock-forming and trace elements in the samples of atmospheric aerosol collected on air filters and in snow samples taken in the period 1980-97. Based on their REE patterns, we have estimated the role of global and regional supply of finely dispersed detritus in the sedimentation in Lake Baikal. A comparative analysis of the elemental composition of suspensions of the main rivers feeding the lake was performed. The earlier and newly determined contents of REE, Fe, Hf, Th, and Rb in the samples are compared with the clarkes of these elements in continental clays.
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I. S. Lomonosov, V. S. Antipin, T. K. Lomonosova, and A. E. Gapon
Keywords: Water catchment basin, Baikal, solid runoff, geochemistry, suspended and driven drift, bottom sediments, sedimentation, mineral associations, petrographic provinces
Pages: 278-297
Abstract >>
We have studied the relations of the composition of the solid runoff of rivers in the Baikal basin with mineralogy and geochemistry of bedrocks of recognized feeding petrographic provinces
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A. D. Duchkov, T.-С. Lee, and S. G. Morozov
Keywords: Temperature, thermal-conductivity coefficient, heat flow, mathematical modeling, underwater boreholes, bottom sediments, Lake Baikal
Pages: 298-307
Abstract >>
Thermal conductivity of rocks is a key parameter in heat flow determination. Thermal conductivity of the Baikal bottom sediments in cores from first underwater boreholes (BDP-93 and BDP-96) was measured by a needle probe and a thermal-conductivity comparator, and the two methods showed a difference of up to 30-50% in the values of both thermal conductivity and heat flow. In this study we used a new method implying evaluation of thermal conductivity of sediments through interpretation (inversion modeling) of temperature field recovery in boreholes after the cessation of drilling. The modeling parameters are steady-state temperature and thermal conductivity of bottom sediments at a depth of temperature monitoring. As a result, it was concluded that the needle probe measurements are reliable, and the thermal-conductivity comparator cannot be used to study unconsolidated sediments with water contents above 40%. The obtained estimates of steady-state temperature and geothermal gradient confirmed that the heat flow is relatively low (about 50 mW/m2) in the Bugul'deika saddle (BDP-93) and high (78 mW/m2, an updated value) in the axial part of the Akademichesky Ridge (BDP-96). The new method allowed us to estimate, for the first time, the thermal-diffusivity coefficient and the specific heat capacity of the Baikal sediments. Thus, the numerical analysis of temperature monitoring data permits estimation of all geothermal parameters of sediments.
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K. Zh. Seminskii, E. B. Karabanov, and M. I. Kuz'min
Keywords: Fractures, sediments, Baikal basin, joints, rank, fracturing zones, rifting, Baikal Drilling Project
Pages: 308-318
Abstract >>
Structural studies of BDP-98 core recovered during deep drilling on the Akademichesky Ridge (Baikal Drilling Project) have shown that the Baikal bottom sediments are cut by tension and shear joints of various scales, locally clustered into zones of fracturing. Specific features of the fractures, formed under the conditions of rifting and diagenesis, are related to their latent character, effects of fluid pressure, prevalently normal geometry of extensional jointing, and the structure of the fracturing zones which favors horizontal extension. The obtained results reveal the regularities of active extensional fracturing, as the latter in the case of Baikal is not overprinted with earlier deformation.
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O. V. Levina, V. A. Bychinskii, O. A. Proidakova, O. Yu. Astrakhantseva, and L. A. Pavlova
Keywords: Biogenic silica, sedimentation, thermodynamic indices
Pages: 319-328
Abstract >>
Thermodynamic indices of biogenic silica have been calculated on the basis of data of X-ray spectral electron probing and the chemical composition of diatom valves. Application of these new data to a physicochemical model for Lake Baikal allowed us to put forward a new concept of biogenic-silica dissolution, which explains the constant concentration of silicium in the Baikal water. The data also suggest that the conservation of biogenic silica in bottom sediments depends on the amorphous state of SiO2 making up the valve. Preliminary data on the involvement of biogenic opal in diagenesis of the bottom sediments are reported.
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V. M. Gavshin, V. A. Bobrov, and O. M. Khlystov
Keywords: Paleoclimatic record, diatom oozes, sedimentation, Lake Baikal
Pages: 329-338
Abstract >>
The Upper Pleistocene paleoclimatic records according to data of deep-water drilling in the Black Sea and Lake Baikal have been correlated. It has been shown that in both basins the two last interglacials were characterized by intense diatom sedimentation. It is stated that the appearance of diatom oozes in the sediments is related to an increased inflow of dissolved silica and nutrient salts. In oceans, this occurred during a rise of internal water, and on continents it was caused by surface runoff in the epochs of intense chemical weathering. The association of biogenic silica with uranium and organic matter (mainly humic acids) occurs not in Lake Baikal only but is also characteristic of upwelling zones, where sedimentation of humic acids and uranium is believed to occur at the water-bottom boundary. It has been found that the Baikal diatom sediments, already enriched in uranium in the superficial layer, further accumulate it immediately beneath the redox boundary. It has been demonstrated that the distribution of "clastophilic" elements in the column of the Upper Pleistocene Baikal sediments is a mirror image of distribution of biogenic silica as a thinner. Each event recognized in the oceanic paleoclimatic record in this time range is clearly pronounced in the sediment columns of the Akademichesky Ridge in Lake Baikal.
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H. Sakai, Sh. Nomura, S. Araki, K. Kashiwaya, Y. Tani, Y. Shibata, T. Kawai, V. A. Kravchinskii, J. Peck, and J. King
Keywords: Bottom sediments, gravity cores, magnetic susceptibility, anisotropy of magnetic susceptibility
Pages: 339-347
Abstract >>
Magnetic susceptibility was studied on short sedimentary cores (a few meters) from lakes Baikal and Biwa. Measurements of cores less than 1 m long showed that the Baikal samples have oblate anisotropy ellipses with nearly vertical short axes, whereas in the Biwa cores these axes are nearly horizontal and their oblate geometry is poorly pronounced. The difference in anisotropy of magnetic susceptibility of the cores from the two lakes may be due to different depositional environments (water depth at the sampling site in Baikal was 200 to 1600 m, and that in Biwa was a few tens of meters). The magnetic susceptibility anisotropy increases down the cores and reaches a stable value at a certain depth. It shows a direct correlation with variations in water depth at sampling sites. The hydraulic pressure on the bottom sediments may be related to the depth of magnetic susceptibility saturation. Magnetic susceptibility of the Ver-99 gravity core recovered on the opposite side of Lake Baikal in the Selenga pro-delta varies broadly in the age region of 11 to 12 ka, and anisotropic parameters show the same changes within these age intervals. The magnetic susceptibility of the Ver-97 st. 6 gravity core from the Akademichesky Ridge exhibits similar variations. The succession of magnetic susceptibility fluctuations is possibly related to the cooling event of Younger Dryas (11 to 12 ka BP). At that stage, a significant sediment transport may have occurred over a great area of Lake Baikal. The age-dependent fluctuations in magnetic susceptibility in the Ver-97 core show a nearly perfect correlation with variations in  18
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Yu. P. Troshin, I. S. Lomonosov, T. K. Lomonosova, N. N. Bryukhanova, A. N. Gvozdkov, V. F. Geletii, L. L. Petrov, I. V. Sandimirov, A. M. Spiridonov, and L. L. Tkachenko
Keywords: Geochemistry, sediments, ore-forming elements, differentiation, organic matter, clay minerals, Lake Baikal
Pages: 348-361
Abstract >>
The regularities of distribution of S, Se, Te, U, Mo, B, P, Cu, Ag, Au, Sn, Zn, Pb, and organic carbon in Cenozoic sediments of various taphrogenic depressions in the Baikal Rift Zone have been studied. The fine-grained carbonaceous deposits of all depressions, particularly carbon partings and lutites of Lake Baikal, have concentrations of U several times higher than its clarke. The sediments of some river valleys are noticeably enriched in Au, which was supplied there from gold-ore deposits of sourcelands.
Organic matter and clayey sediments (or their lithified analogs) are the major concentrators and carriers of the above-listed elements. The most differentiated (according to the content of organic carbon) rocks exposed by BH-S-1 in the Tunka depression, where the concentration of Corg varies from 0.3 to 83% (in coal), show a certain distribution of elements between the organic and clayey matter, in accordance with their strength of bond with the latter: Corg-S-Se-U-Ag-Mo-B-Au-Te-Cu-Sn-Pb-Zn-clay.
The organic matter concentrates S, Se, U, Mo, and Ag, and the clayey matter concentrates Pb, Zn, Sn, and Cu. Gold and tellurium (which can bind with B, Mo, and Cu) behave in a specific way and indifferently with respect to the organic and clayey matter of the sediments, forming an independent terrigenous sedimentary material, probably, bearing native gold. Sometimes additional concentrators - phosphates, sulfates, and sulfides - are produced. In places, the behavior of these elements is different and even more intricate as a result of changes in the granulometric and mineral compositions of sediments. Diagenesis leads to a stronger separation of elements. Groups of elements tending to isolation as a result of differentiation at the sedimentation and diagenesis stage form associations typical of various ore deposits. It is suggested that the chemical processes of deposition and early diagenesis of the formed sediments in sedimentation basins are the initial stage of pre-ore differentiation of ore-forming elements in the originating source of matter for future deposits. This initial differentiation already exhibits the specific features of the forthcoming ore genesis.
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L. Z. Granina, E. Callender, I. S. Lomonosov, V. D. Mats, and L. P. Golobokova
Keywords: Pore water, anomalies, concentrations, faults, ions, Lake Baikal
Pages: 362-372
Abstract >>
Anomalies in pore water composition have been found in the 100m long core BDP-93 that was drilled in southern Lake Baikal, in four piston cores (1 to 8 m in length) taken from the same region, and in recent sediments from Frolikha Bay, a hydrothermal vent site in northern Lake Baikal. Pore water anomalies are manifested as significant increases in concentration of sulfates, bicarbonates, chlorides, and the ions of alkali and alkali-earth metals. Anomalies were found at different depths below the sediment-water interface (from centimeters to tens of meters), and the level of pore water enrichment in these components varies from station to station.
Anomalies have specific features in each of the Lake Baikal basins. It is shown that there is a genetic relationship between subaquatic and terrestrial centers of thermal-water discharge in northern Lake Baikal. These anomalous pore-water concentrations are presumably due to the leaching of ambient sediments
In southern Lake Baikal, in the Selenga river delta, ground waters of specific composition that are relics of ancient salt lakes could serve as a source of anomalous concentrations in pore-water components. Their influence may be realized through the extensive zones of increased permeability.
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O. M. Khlystov, V. D. Mats, and M. de Batist
Keywords: Continuous seismic profiling, seismostratigraphy, correlation, sediments of Lake Baikal
Pages: 373-383
Abstract >>
The paper presents new details of the structure of the basement and sedimentary cover of the southwestern edge of the North Baikal basin. The basement structure involves smaller-scale structures (Maloe More basin, Zama basin, and Zunduk-Zama horst), which, in turn, comprise third-order features. The presence of several en-echelon NE striking sub-basins within the Maloe More and Zama basins indicates that the tectonic framework of the region formed by listric and dextral faulting. Seismostratigraphy data and analysis of uppermost bottom sediments from BDP-96 and BDP-98 cores revealed three seismic layers in the sediment section, which are separated by discontinuities and can be correlated with deposits exposed on land in the neighboring Ol'khon region. Unit A' (X) correlates with the Lower-Middle Oligocene Ular'yar Formation, unit A, with the Lower-Middle Miocene Tagai Formation, and unit B, with the Upper Miocene-Pliocene Sasa Formation and with Quaternary deposits. The upper section of the Maloe More fill includes a separate seismic horizon correlatable with a layer of widely distributed fine-grained sand. Unit B, comprises three deposition centers within the limits of the Maloe More basin, i.e., large lakes existed in the region prior to the final stage of transgression from the North Baikal basin.
Thus, the southwestern edge of the Baikal basin has an intricate structure and underwent a complex evolution.
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A. P. Fedotov, E. V. Bezrukova, S. S. Vorob'eva, O. M. Khlystov, O. V. Levina, I. B. Mizandrontsev, G. F. Mazepova, A. R. Semenov, T. O. Zheleznyakova, S. M. Krapivina, E. P. Chebykin, and M. A. Grachev
Keywords: Climate fluctuations, Holocene, Late Pleistocene, bottom sediments, carbonate abundance, Lake Hovsgol
Pages: 384-390
Abstract >>
Results of analyses of the upper sedimentary layer from Lake Hovsgol (Mongolia) sampled with bottom cores in the Northern lake basin are presented. The core is characterized; the contents of moisture and biogenic silica as well as the composition of diatom species are determined at each 2 cm using light microscopy method. Palynological analysis is performed at continuous 2 cm intervals. The content of carbonate CO2 is determined at each 10 cm.
The core obtained covered the end of glaciation and the entire Holocene. The Holocene boundary is determined by correlation of the studied core with numerous cores from other Mongolian lakes studied earlier. The mean sedimentation rate in the Northern basin in the Holocene was 7-8 cm per 1000 years.
The Pleistocene sediments contain a large amount of carbonates. In the Holocene sediments their concentration decreased abruptly.
The data obtained suggest convincingly that sampling of long sedimentation cores from Lake Hovsgol and their complex analysis can give very important information about the Pleistocene paleoclimates and, in particular, a deeper insight into the sedimentary record of Lake Baikal.
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