Climatic factors as risks of recent ecological changes in the shallow zone of Lake Baikal

Eutrophication processes have been recorded in many world’s freshwater reservoirs, which are sources of drinking water. More and more investigations show that global warming is the main natural factor that causes eutrophication. In recent years, signs of eutrophication have also been recorded in Lake Baikal containing 20% of the world’s freshwater reserves. Therefore, we performed the first comprehensive analysis of long-term changes in climatic parameters capable to provoke negative changes in the shallow zone. The largest number of anomalies of climatic indices has been recorded in the 21st century. Moreover, the current decade has been the most favorable for the emergence of negative processes in the lake (outbreak of the mass growth of algae and aquatic vegetation, rotting of their remains at the bottom and on the shores of the lake, changes in the structure and zoning of biocoenoses, etc.). The main natural conditions favoring the emergence of negative signs are elevated temperatures of the air and lake shore water, reduced amount of precipitation, reduced inflow of river waters into Baikal and lowering of its water level, low-water season, and weakening of wind currents, water exchange processes, and, as a result, water self-purification. In the period of continuing global warming, it is necessary to study the climate effect on the processes in the shallow zone and to carry out long-term monitoring for elucidation of recent and expected changes in the ecological state of Lake Baikal and for their valid interpretation.     

Climate change in Lake Baikal: diatom evidence in an area of continuous sedimentation

The presence of inhomogeneous sedimentation is acknowledged as being an important problem in palaeolimnological studies. Sediment records can be disturbed by erosional and redepositional events, which redeposit microfossils within a basin and may then lead to misinterpretations of fossil diatom assemblages. This study uses a combination of sedimentological tools, magnetic susceptibility measurements and high-resolution diatom analysis to show that a sediment core, BAIK80, taken in 345 m water depth from a shoulder region in the North Basin of Lake Baikal, is free of disturbances. Our results confirm that the sediment record is consistent and continuous for the uppermost sediment. Consequently, the fossil diatom data can be used to establish a continuous record of past climate variability over approximately the past 1300 years. Distinct changes occur in downcore abundances of endemic taxa Aulacoseira baicalensis and Cyclotella minuta, and principal components analysis (PCA) indicates a gradual transformation of taxa over the past 1300 years. These changes are likely to be related to climate, although definite links still have to be established. Received: 15 December 1998 / Accepted: 13 September 1999     

Sampling, Sample Preparation and ICP-MS Chemical Analysis of Lake Baikal Sponges

Procedures for sampling, sample preparation and ICP-MS analysis of endemic sponges from Lake Baikal have been developed. Sample decomposition was carried out using an open acid decomposition with ultrasound treatment. The distribution of nineteen elements (Mg, Al, P, Ca, Ti, Mn, Co, Ni, Cu, Rb, Sr, Y, Cd, Ba, La, Ce, Pb, Th and U) in different parts of a sponge's body (outer and inner layers and layers adjacent to the substratum) was studied. Detection limits were determined; these ranged from 0.013 to 4.12 μg g^-1 for trace elements and from 23 to 130 μg g^-1 for biogenic elements. The degree of elemental uptake by living substances is discussed with regard to the environment.     

新疆和田玉和俄罗斯贝加尔湖地区软玉的岩石学特征研究

通过对新疆和田玉以及俄罗斯贝加尔湖地区软玉的化学成分、矿物组成、结构构造等方面的研究和对比,从岩石学的角度较系统地总结了两者的异同点,指出两者主要成分和主要矿物组成是近似的,但主要结构有区别,因而在外观上也有一定的差别,这对于两者的开发和利用有重要的实际意义.     

Stratigraphic and structural evolution of the Selenga Delta Accommodation Zone, Lake Baikal Rift, Siberia

Seismic reflection profiles from the Lake Baikal Rift reveal extensive details about the sediment thickness, structural geometry and history of extensional deformation and syn-rift sedimentation in this classic continental rift. The Selenga River is the largest single source of terrigenous input into Lake Baikal, and its large delta sits astride the major accommodation zone between the Central and South basins of the lake. Incorporating one of the world's largest lacustrine deltas, this depositional system is a classic example of the influence of rift basin structural segmentation on a major continental drainage. More than 3700 km of deep basin-scale multi-channel seismic reflection (MCS) data were acquired during the 1989 Russian and the 1992 Russian–American field programs. The seismic data image most of the sedimentary section, including pre-rift basement in several localities. The MCS data reveal that the broad bathymetric saddle between these two major half-graben basins is underlain by a complex of severely deformed basement blocks, and is not simply a consequence of long-term deltaic deposition. Maximum sediment thickness is estimated to be more than 9 km in some areas around the Selenga Delta. Detailed stratigraphic analyses of the Selenga area MCS data suggest that modes of deposition have shifted markedly during the history of the delta. The present mode of gravity- and mass-flow sedimentation that dominates the northern and southern parts of the modern delta, as well as the pronounced bathymetric relief in the area, are relatively recent developments in the history of the Lake Baikal Rift. Several episodes of major delta progradation, each extending far across the modern rift, can be documented in the MCS data. The stratigraphic framework defined by these prograding deltaic sequences can be used to constrain the structural as well as depositional evolution of this part of the Baikal Rift. An age model has been established for this stratigraphy, by tying the delta sequences to the site of the Baikal Drilling Project 1993 Drill Hole. Although the drill hole is only 100 m deep, and the base of the cores is only ∼670 ka in age, ages were extrapolated to deeper stratigraphic intervals using the Reflection-Seismic-Radiocarbon method of Cohen et al. (1993). The deep prograding delta sequences now observed in the MCS data probably formed in response to major fluctuations in sediment supply, rather than in response to shifts in lake level. This stratigraphic framework and age model suggest that the deep delta packages developed at intervals of approximately 400 ka and may have formed as a consequence of climate changes affiliated with the northern hemisphere glaciations. The stratigraphic analysis also suggests that the Selenga Basin and Syncline developed as a distinct depocentre only during the past ∼2–3 Ma. Received: 1 December 1999 / Accepted: 26 January 2000     

Lake-level changes during the past 100,000 years at Lake Baikal, southern Siberia

Lake-level changes inferred from seismic surveying and core sampling of the floor of Lake Baikal near the Selenga River delta can be used to constrain regional climatic history and appear to be correlated to global climate changes represented by marine oxygen isotope stages (MIS). The reflection pattern and correlation to the isotope stages indicate that the topset and progradational foreset sediments of the deltas formed during periods of stable lake levels and warm climatic conditions. During warm stages, the lake level was high, and during cold stages it was low. The drop in the lake level due to cooling from MIS 5 through MIS 4 is estimated to be 33-38 m; from MIS 3 through MIS 2, it fell an additional 11-15 m. Because the lake level is chiefly controlled by evaporation and river input, we infer that more water was supplied to Lake Baikal during warm stages.     

Paleoenvironmental proxy records from Lake Hovsgol, Mongolia, and a synthesis of Holocene climate change in the Lake Baikal watershed

Here we discuss paleoenvironmental evolution in the Baikal region during the Holocene using new records of aquatic (diatom) and terrestrial vegetation changes from Hovsgol, Mongolia's largest and deepest lake. We reconcile previous contradictory Baikal timescales by constraining reservoir corrections of AMS dates on bulk sedimentary organic carbon. Synthesis of the Holocene records in the Baikal watershed reveals a northward progression in landscape/vegetation changes and an anti-phase behavior of diatom and biogenic silica proxies in neighboring rift lakes. In Lake Baikal, these proxies appear to be responsive to annual temperature increases after 6 ka, whereas in Lake Hovsgol they respond to higher precipitation/runoff from 11 to 7 ka. Unlike around Lake Baikal, warmer summers between 6 and 3.5 ka resulted in the decline, not expansion, of forest vegetation around Lake Hovsgol, apparently as a result of higher soil temperatures and lower moisture availability. The regional climatic proxy data are consistent with a series of 500-yr time slice Holocene GCM simulations for continental Eurasia. Our results allow reevaluation of the concepts of ‘the Holocene optimum’ and a ‘maximum of the Asian summer monsoon’, as applied to paleoclimate records from continental Asia.     

Multi-Wavelength Synchrotron Radiation XRF Determination of U and Th in Sedimentary Cores from Lake Baikal

A new technique for the determination of uranium and thorium in lacustrine sediments is based on non-destructive synchrotron radiation X-ray fluorescence analysis (SR-XRF) of sediment samples using monochromatic beams of different energies as excitation sources, with the recording and subsequent iterative processing of the X-ray fluorescence spectra. The technique has a multielement capability and enables fast, simultaneous analysis of a few tens of elements. The proposed SR-XRF technique was tested against INAA and ICP-MS methods and showed a number of advantages with a generally good correlation of results by the three methods. Uranium and Th profiles have been measured at a time resolution of 2 kyr in a drill core (BDP-96) from Lake Baikal bottom sediments deposited between 780 and 40 kyr B P. During this time span, peaks in the U and U/Th concentration marked warm climates. Oscillations of U and U/Th in Baikal bottom sediments during the Brunhes chron reflect climate-induced global change in the volume of polar ice, controlled by long-term cyclicity of the Earths orbital parameters. The response of these warm periods is similar to that observed earlier in shorter cores that span the two last interglacials (220-0 kyr BP).     

Sedimentation processes and new age constraints on rifting stages in Lake Baikal: results of deep-water drilling

 With this paper we present a first attempt to combine the direct results on lithology, composition and age dating in the boreholes BDP-93, BDP-96 and BDP-97 with geological and seismic data from the areas where those sections were drilled. The sedimentary environments represented by the BDP boreholes are markedly different and possess characteristic lithological features. The results of the deep drilling provide the essential means for testing numerous age models used in geological reconstructions of the Lake Baikal rifting dynamics. Neither the basin-wide unconformity interpreted from seismic data, nor the interpreted change from shallow-water to deep-water facies at the boundary of the seismic stratigraphic complexes were found in the BDP-96 boreholes on Academician Ridge. Also, lithology does not support the proposed reconstructions of intense lake level fluctuations and transgressions during the Pliocene at Academician Ridge. The continuous deep-water hemipelagic sedimentation at Academician Ridge has existed for the past 5 Ma. The beginning of an intense rifting phase of the Neobaikalian sub-stage and related drastic changes in sedimentation processes were interpreted on seismic sections as the basin-wide unconformity B10. Different age estimates for this boundary ranged from Late Pliocene (3.5 Ma) to Plio-Pleistocene boundary. As shown by BDP-96 borehole, B10 is associated with a lithological change from diatomaceous ooze to dense silty clay and not with an erosional contact. The new age for this boundary in BDP-96 is approximately 2.5 Ma. This new age constraint suggests that the upper sedimentary strata of Northern Baikal (1.5–1.7 km thick) have formed during the past 2.5 Ma with average sedimentation rates of 60–70 cm/ka. The BDP-93 boreholes at Buguldeika suggest that uplift in Primorsky Range took place prior to 1.07–1.31 Ma, a date which exceeds the age of previous geological models. Received: 12 March 1999 / Accepted: 10 February 2000     

A computer-assisted thin-section study of Lake Baikal sediments: a tool for understanding sedimentary processes and deciphering their climatic signal

A freeze-drying technique for cutting thin-sections of soft sediments without disturbance is used to study several Lake Baikal sedimentary microstructures. Image analysis methodology is applied to selected thin-sections. This new technique provides quantification of the size, shape, orientation and packing of the objects forming the sedimentary structures. Sedimentary processes, which were previously poorly documented, have been identified, and others are better understood. Spheroidal lens-like pure aggregates of the diatom genus Synedra are found in hemipelagic sediments, providing a new insight into their traditional paleoecological interpretation. They are possibly related to a transportation mechanism from the littoral zone or to lacustrine snow. Laminae of Aulacoseira have also been recorded. Evidence of rapid sedimentation suggests they are due to massive algal blooms. The depositional mechanism that was suggested by other studies for explaining the laminations at the Buguldeika uplift is confirmed: the hemipelagic sedimentation is interrupted by terrigenous pulses due to discharge events. The sedimentation rate appears to be increasing during these pulses. Preliminary results from the Academician Ridge show stronger microbioturbation during cold periods. This observation strengthens the hypothesis of intense water circulation during colder times. Thin-section image analysis provides crucial information for deciphering lacustrine records and their regional and palaeoclimatic significance. Received: 27 November 1998 / Accepted: 13 September 1999     

Dynamic causes for the opening of the Baikal Rift Zone: a numerical modelling approach

Previous dynamic models of the Baikal Rift Zone (BRZ) are mostly two-dimensional on vertical plane. In this study, a numerical model of neotectonics in the region on map view was constructed using the adapted PLATES program. The present work is an attempt to test different mechanisms for opening Baikal Rift by comparing the modelled and observed stress and strain rate fields. The following rifting scenarios were tested: (1) pure northwest–southeast extension, (2) pure northeast–southwest compression, (3) oblique rift opening and (4) combined northwest–southeast extension and northeast–southwest compression. The models are calibrated using geologically and GPS-derived strain rates and stress-tensor determinations from fault-slip data and earthquake focal mechanisms. The most successful model requires a combination of NE–SW compression and orthogonal extension. The model results indicate that the present extensional regime in BRZ can be explained by combining the India plate indentation northward into Eurasia, east–west convergence between the North America and Eurasia plates and southeastward extrusion of the Amur plate in northeastern Asia. Predicted fault-slip rates for the best-fit model are consistent with the observed Holocene fault-slip rates in the Lake Baikal region. The generally accepted rotation of the Amur and Mongolia microplates are used as independent constraints for the choice of the best-fit model. These data correlate well with the predicted direction of rotation in our best model.     

俄罗斯贝加尔裂谷带中呼兰霍博克火山岩岩石学及地球化学研究

位于贝加尔裂谷带通京盆地中的呼兰霍博克火山火山锥由火山弹、火山灰等火山碎屑岩和基性熔岩(橄榄玄武岩)组成.橄榄玄武岩中橄榄石可分为具有较高Mg#值的捕虏晶和Mg#值相对较低的斑晶.部分斜长石斑晶具有核.幔.边结构,且幔部发生减压分解,一些单斜辉石晶体(俘虏晶)边部发生了减压分解.根据岩石的化学成分,该玄武岩属于橄榄粗玄岩系列,轻稀土强烈富集,重稀土相对亏损,轻重稀土之间分异较大,具有与OIB相似的微量元素和同位素地球化学特征.岩石学和元素地球化学研究表明,该橄榄玄武岩的源区和岩浆的形成可能与地幔柱活动有关;岩浆演化经历了压力骤减的过程,在岩浆快速上升过程中,深部形成的矿物(可能是地幔矿物的俘虏晶)减压分解.快速上升的岩浆几乎未受大陆地壳的混染,仅捕获了少量流纹质熔体.     

Morphotectonics of lacustrine basins: The Baikal rift zone as an example

Formation mechanisms and development of numerous and morphologically diverse lacustrine basins of the Baikal rift zone are considered in terms of morphotectonics. All the representative lake species are characterized, and their regional morphotectonic classification is suggested.     

贝加尔裂谷带通京盆地呼兰霍博克火山的玄武岩岩石学和地球化学特征

位于贝加尔裂谷带西南端通京盆地的呼兰霍博克火山为玄武岩质碎屑锥,玄武岩由高拉长石、贵橄榄石、普通辉石和火山玻璃组成,其矿物组成及SiO2-（Na2O＋K2O）图和Hf-Th-Ta图指示为碱性玄武岩.CIPW标准矿物特征、岩石化学成分和单斜辉石化学成分特征表明岩石属碱性系列,钠质型.稀土元素和微量元素的地球化学特征表明岩石为裂谷初期玄武岩.初步推断原始岩浆来源于上地幔,斑晶可能于16.5 km深处的次生壳层岩浆房结晶.     

Heat flow and gas hydrates of the Baikal Rift Zone

Multi-channel seismic studies (MCS), performed during a Russian expedition in 1989 and a joint Russian-American expedition in 1992, have for the first time revealed a “bottom simulating reflector” (BSR) in Lake Baikal. These data have shown that gas hydrates occur in the southern and central basins of Lake Baikal in those places where the water depth exceeds 500–700 m. Four types of tectonic influence on the distribution of the gas hydrate were revealed: (a) Modern faults displace the BSR as they do with normal seismic boundaries. (b) Older faults displace normal reflectors, whereas the BSR is not displaced. (c) Modern faults form zones, where the BSR has been totally destroyed. (4) Processes that occur within older fault zones situated close to the base of the hydrated sediment layer lead to undulations of the BSR. The thickness of the hydrate stability field (inferred from seismic data) ranges between 35 and 450 m. Heat-flow values determined from BSR data range from 48 to 119 mW/m². A comparison between heat-flow values from BSR data and values measured directly on the lake bottom shows an overall coincidence. Changes in water level and bottom-water temperature that occurred in the past have had no noticeable influence on the present BSR depths or heat-flow values. Determination of deep heat flow from BSR data is in this case more reliable than by direct measurements. Received: 10 December 1998 / Accepted: 15 November 1999     

A reassessment of late glacial – Holocene diatom oxygen isotope record from Lake Baikal using a geochemical mass‐balance approach

We present a new palaeoenvironmental record of hydrological variability in Lake Baikal, based on re‐modelled δ¹⁸O_diatom values of diatom silica (δ¹⁸O_modelled), where the residual contaminants are identified and compensated for using electron optical imaging and whole‐sample geochemistry. δ¹⁸O_modelled interpretations are based on the balance between rivers with high δ¹⁸O values and rivers with low δ¹⁸O values. Isotopic variability is related to latitudinal differences in precipitation which feed these rivers. The δ¹⁸O_modelled record suggests that rather moist conditions prevailed in the Lake Baikal region during the latter stages of the Younger Dryas. Throughout the Holocene, episodes of low δ¹⁸O_modelled values are, in general, in good agreement with increases in percentage haematite‐stained grains in North Atlantic sediments (indicative of ice‐rafted debris events). Rivers with southerly catchments dominate fluvial input especially between c. 3.3 and 2 cal ka BP, concurrent with high precipitation in the Lake Baikal region. Copyright © 2011 John Wiley & Sons, Ltd.     

Sorption of P by ferric hydroxide film, cover particles of sediments of Lake Baikal

We investigated in more detail the adsorption phenomenon which was described earlier. It was clearly established that the hydroxyl apatite was not participated in P adsorption. This phenomenon takes place because of ferric hydroxide film. Modem sediments from the Southem Basin of Lake Baikal were taken and stirred with Baikal water. Carrier-free [^32p]-orthophosphate was added in this system. Similar experiments were made with carrier-free [^35S]-sulphate. Sulphate stayed in supematant completely. The influence of pH on the system with inorganic phosphate was also studied. In low alkali conditions phosphate migrated in supematant, in low acid, in sediments. Baikal sediment was stripped of iron-hydroxous film by treatment with 1% oxalic acid. Investigation of striped sediment shown that phosphate stays in supematant only. Hence, hydroxyl apatite cannot be the phase of the sediments of Lake Baikal which binds phosphate. This all showed by our group before. Now we have found the limit of phosphate sorption in Lake Baikal sediments and the stehiometry of the sorption. The sorption limit of Lake Baikal sediments was studied. An experiment with inorganic ^31P phosphate was made. 0.025% K2HPO4 solution with adding ^32P radioactive mark into it was prepared. 100 μL of mixture of ^31PO4^3- and ^32PO4^3- seven times were added in a ＂Baikal water-Baikal sediment＂ system and blank （100 ml BW only）. Concentrations of inorganic ^31PO4^3- were very low so the bend dot on the diagram was found and sorption limit of sediment was estimated. Baikal sediment stopped assimilating phosphate in the bend dot. The stehiometry of sorption was estimated by supematant-sediment radioactive ratio, which equals 3, that is, three Fe （Ⅲ） atoms associate one PO4^3- anion. The only Fe （Ⅲ） substance which could associate P is -Fe-O-Fe- polymer film. It also dissolves in acid conditions.     

试论残留型盆地研究思路和油气勘探方法

残留型地具有抬升剥蚀剧烈,原形盆地难以恢复,经历多期构造运动的改造和建造油气成藏动力学过程复杂,热演化程度较高,油气保存条件复杂等特点,但是残留型盆地油气资源丰富,勘探前景广阔,依据残留型盆地的特征和油气资源潜力,提出应全面,发展地认识盆地,静动结合地研究盆地,运用先进而实用的新技术新方法评价盆地,按照勘探程序勘探盆地,在研究工作上应以分地及其邻区作为整体研究对象,以区域地质研究一石油地质研究－综     

微生物改造有机质不同演化阶段油气的生成

石油是生物地质作用的产物,沉积物中有机质的组成和结构影响着石油天然气的生成。微生物改造有机质形成石油、天然气具有明显的阶段性:1)易溶于水的有机质和分子量小、成分简单的化合物优先参与到成油中形成低熟油。2)成熟油的有机母质主要为来自水生生物、藻类的脂肪和蛋白质,其次为来自陆源有机质中的碳水化合物脂肪分解菌、蛋白质分解菌、产氢菌等;脂肪酸初始阶段不溶于水,只有当环境中不存在占优势的其他碳源物质时,微生物才能利用和分解脂类进行生长。3)高演化阶段生存着大量的嗜热、超嗜热产甲烷菌,来自于陆源植物的纤维素、木质素、高分子聚合物等许多在成熟阶段难以降解的有机质在高演化阶段可以发生降解。成油过程要经过降解有机质、去除含氧基团、产氢菌产氢、耗氢菌用氢等过程,较成气过程更为复杂。     

南方油气勘探的突破贵在坚持不懈

中国南方的地质条件复杂,油气勘探的历程曲折。但只要在复杂地区寻找相对稳定的地区,发现大型油气田是有可能的。提出当前油气勘探的策略应做到思想坚定、思路常新、技术跟上、重点突出、工作精细。