800-yr-long records of annual air temperature and precipitation over southern Siberia inferred from Teletskoye Lake sediments

A unique 800-yr-long record of annual temperatures and precipitation over the south of western Siberia has been reconstructed from the bottom sediments of Teletskoye Lake, Altai Mountains using an X-ray fluorescence scanner (XRF) providing 0.1-mm resolution timeseries of elemental composition and X-ray density (XRD). Br content appears to be broadly correlative with mean annual temperature variations because of changes in catchment vegetation productivity. Sr/Rb ratio reflects the proportion of the unweathered terrestrial fraction. XRD appears to reflect water yield regime and sediment flux. Sedimentation is rather continuous because annual clastic supply and deposited mass are the same. The artificial neural networks method was applied to convert annual sedimentary time-series of XRD, Br content, and Sr/Rb ratio to annual records of temperature and precipitation using a transfer function. Comparison of these reconstructed Siberian records with the annual record of air temperature for the Northern Hemisphere shows similar trends in climatic variability over the past 800 yr. Estimated harmonic oscillations of temperature and precipitation values for both historical and reconstructed periods reveal subdecadal cyclicity.     

滇池湖泊沉积物中游离类脂物的有机地球化学特征

在对滇池湖泊沉积物有机质总体特征分析的基础上,对沉积物中可溶性有机质的组成进行了定量测定,并揭示了其剖面变化特征.研究结果表明:(1)正构烷烃组分具有较强的稳定性,反映出滇池沉积有机质以菌藻类来源为主,沉积柱上、下两段存在陆源高等植物输入相对增加的特征,且从下往上存在草本植物相对贡献增加的特征;(2)脂肪醇组分,以具有强烈偶碳优势的高碳数脂肪醇为主,反映了沉积有机质中陆源输入的部分;(3)脂肪酸组分揭示出可溶有机质中以浮游植物贡献为主,局部层段存在相对较强的细菌改造作用.因此,湖泊沉积物记录了滇池从一个贫营养的湖泊演变成富营养化湖泊的过程,特别是最近几十年,滇池内源有机物和陆源有机物的输入都呈现快速增长的趋势,结合同位素组成特征表明滇池进入了重富营养化阶段.     

太湖全新世沉积物的古盐度指标及其环境意义

沉积物中的Ｃａ／（Ｆｅ＋Ｃａ）比值和硼含量随水体含盐度的高低而相应增减，它们都是较好的古盐度指标。本文对太湖全新世的沉积物进行了古盐度指标的分析。并与现代湖泊和海洋沉积物作了对比，结果反映东太湖为陆相沉积环境，而西太湖则主要为海相沉积环境。此结论与古生物化石的结论一致，从而证明了太湖地区于全新世期间经历了大规模的海侵，并形成海湾－湖环境。同时也证明了这些古盐度指标是行之有效的。     

Six thousand years of records of metal mining and utilization from lake sediments in central China

A sediment core from the Liangzhi Lake, Hubei Province in central China, was used to assess metal usage and accumulation in the past 6000＋ years in China. The concentrations of trace metals, including Cr, Cu, Pb, Ni and Zn, and major elements, Ca, Fe and Mg, in the ^14C-dated sediment core were analyzed. Historical trends of metal inputs to the Liangzhi Lake from 5000 B.C. to the present were recorded in the sediments, representing over 6000 years of metal mining and utilization history in China. The concentrations of Cu, Ni, Pb and Zn have increased gradually since 3000 B.C., indicating the start of the Bronze Age era in ancient China, until the period 467-76 B.C. During the period of 467-76 B.C., there had been a rapid increase in the concentrations of these metals in the sediments, indicating the enormous inputs of these metals at that time. This era corresponded well with the Warring States Period （475-221 B.C.） and early Hart Dynasty （206 B.C.-220 A.D.） of China, during which copper and lead were extensively used in making bronze articles, such as vessels, tools and weapons. During 1876 A.D. to the early 1900s, there was also a significant increase in the metal concentrations, such as Cu, Ni and Pb, which could probably reflect the impact of metal emissions during the early industrial development and wars in China. The Pb isotopic analysis showed that the surface and subsurface sediments had lower ^206Pb/^207Pb, and ^208Pb/^207Pb ratios than the deeper layers, affected by mining activities both during the Bronze Age era and modem times.     

Sterol Distribution in Sediments from Chaiwobu Lake and Caohai Basin and Its Geochemical Significance

In order to understand the distribution characteristics of biomarkers in source rocks,which may be related to organic input,Quaternary sediments from the Caohai Basin and the Chaiwobu Lake were analyzed for sterols,As a result,various sterols,have been found in the sediments.The composition of sterols in the sediments revealed that cholesterols and cholestadienols are more abundant than their C29 counterparts in the Chaiwobu Lake sediments and that C29 sterols are more abundant in the peats from the Caohai Basin,It is also found that stanol/sterol ratios in clays are higher than in peats.Studies show that organic input to the Chaiwobu Lake is mainly plankton and zooplankton and to the Caohai Basin is mainly terrestrial high plant.The authors have proposed that the relative abundance of C27 or C29 sterane in source rocks may reflect input characteristics to some extent and the stanol/sterol ratios may reflect the redox conditions of the depositional environments.     

成都经济区近地表大气尘地球化学基线

成都经济区近地表大气尘中重金属元素含量空间分布显示,经济区中东部高于西部,北部高于中南部,重工业城市高于综合性城市和旅游城市,工矿影响区元素含量总体偏高,人口密集的平原区高于山区。通过标准极限方法确定了近地表大气尘中元素的“极限浓度”,以低于“极限浓度”值统计确定了地球化学基线值：As为28.6mg/kg 、Hg 0.63mg/kg 、Cd 2.94mg/kg、Cr 110mg/kg、Pb 281mg/kg、Ni 32mg/kg、Zn 535mg/kg。近地表大气尘中元素地球化学基线与区域地质背景和矿产开发有关,矿业活动、工业活动及居民生活是造成近地表大气尘中人为扰动元素含量偏高的主要原因。     

成都经济区近地表大气尘地球化学基线

成都经济区近地表大气尘中重金属元素含量空间分布显示,经济区中东部高于西部,北部高于中南部,重工业城市高于综合性城市和旅游城市,工矿影响区元素含量总体偏高,人口密集的平原区高于山区。通过标准极限方法确定了近地表大气尘中元素的“极限浓度”,以低于“极限浓度”值统计确定了地球化学基线值：As为28.6mg/kg 、Hg 0.63mg/kg 、Cd 2.94mg/kg、Cr 110mg/kg、Pb 281mg/kg、Ni 32mg/kg、Zn 535mg/kg。近地表大气尘中元素地球化学基线与区域地质背景和矿产开发有关,矿业活动、工业活动及居民生活是造成近地表大气尘中人为扰动元素含量偏高的主要原因。     

A Holocene climatic record denoted by geochemical indicators from Barkol Lake in the northeastern Xinjiang,NW China

The Barkol Lake, as a closed inland lake, is located at the northeast Xinjiang in northwest China. A combination of geochemical indicators including δ¹⁸O and δ¹³C of carbonate, TOC, carbonate contents, as well as grain size proxies and magnetic susceptibility of sediments obtained from a newly recovered section at this lake, provides a high-resolution history of climatic change in the past 9400 years. Multi-indicators reflect that Holocene climatic change in the study region generally follows the Westerly Wind pattern of Holocene, and three climatic periods can be identified. Between 9400 and 7500 cal a B.P., climate was characterized by relatively drier and colder condition. From 7500 to 5800 cal a B.P., a relatively warmer and moister climate prevailed, but between 5800 and 3500 cal a B.P., climate shifted towards warmer and drier conditions. A relatively colder and wetter climate prevailed during 3500∼1000 cal a B.P., then it changed towards cold and dry between 1000 and 500 cal a B.P.; after 500 cal a B.P., climate changed towards warm and dry conditions again. This study reflects that during the Middle Holocene (from ca 7000 to 3500 cal a B.P.), variations of carbonate δ¹⁸O of sediments from several lakes in the northern Xinjiang were synchronous with that of Qinghai Lake, where was strongly influenced by the South Asian monsoon; however, after 3500 cal a B.P. this consistency was interrupted, possibly resulting from a re-domination of the Westerly Wind and the retreat of South Asian monsoon in the northern Xinjiang.     

Evaluation of environmental status and geochemical assessment of sediments,Manasbal Lake,Kashmir, India

The present study was conducted on the Manasbal Lake (34°14′N: 74°40′E) to assess the geochemical characteristics of the lake bottom sediments, its environmental implications and its response in the local catchment area. This study tracks the spatial distribution of grain size, geochemical analysis, C/N ratio, calcium carbonate (CaCO₃) and organic matter (OM) of the lake bottom sediments. It is observed that the clay fraction (49.79%) is predominant in the lake bottom sediments, followed by silt (35.88%) and sand (14.33%) and its spatial distribution is controlled by water depth. Geochemistry and normalized diagrams for the major oxides and trace elements reveal enrichment of CaO, K₂O, P₂O₅, S, Cl, Ni, Zn and Sr. Chemical index of alteration (CIA) reflects low to moderate weathering intensity and near compositional similarity with the bedrock exposed in the catchment area around the lake. Environmental indices (EF, Igeo) suggest that the sediments are enriched in Cu, Ni, Zn, Cr, Co, Pb followed by Mn content. Pollution load index (PLI) reveal that all the sampling sites reflect low to moderately polluted category except for few stations that are towards the southern and southeastern side of the lake. OM (16.85%), CaCO₃ (14.04%) and C/N ratio (15.5) of the lake bottom sediments is attributed to high organic activity within the lake, shell fragments, contributions from the lake flora and fauna adhering to the clayey silty sediments. The C/N ratio of 15.5 suggests a mixed source of organic matter both terrestrially and in situ formation within the lake. Sulphur and chlorine are high amongst the trace elements suggesting anthropogenic detritus input into the lake and this is due to the chemical fertilizers from the agricultural runoff and organic load into the lake. Thus, the present study suggests that in order to preserve the pristine lake ecology and the environment; continued monitoring and restoration efforts need to be undertaken.     

Environmental evolution recorded by multi-proxy evidence in Lake Chenghai sediments, Yunnan Province during recent 100 years

Lacustrine sediments can provide potential information about environmental changes in the past. On the basis of high-resolution multi-proxy analysis including carbon and nitrogen contents of organic matter, C/N ratios, inorganic carbon contents, and carbon and oxygen isotopic composition of carbonate, together with precise 137Cs dating, the environmental evolution of Lake Chenghai, Yunnan Province, during the past 100 years has been investigated. It is shown that the carbonate in Lake Chenghai is authigenic, and the organic matter is mainly derived from aquatic plants and algae, instead of terrestrial-source materials. The environmental evolution of Lake Chenghai can be diverged into three periods with the contrasting characteristics during the past 100 years. Before 1940, the stable carbon and oxygen isotope values, the poor correlation between them and the lower carbon and nitrogen contents of organic matter suggested that Lake Chenghai was open, and the lake water was oligotrophic during that period. During 1940-1993, the negative δ13C values and the gradual increase of carbon and nitrogen contents of organic matter and C/N ratios indicated that the eutrophication was aggravated. The closeness of Lake Chenghai and human activities may be responsible for this eutrophication. After 1993, notable increases in carbon and oxygen isotopic values of carbonate, carbon and nitrogen contents of organic matter, C/N ratios and inorganic carbon contents demonstrated that the increase of lacustrine productivity and the serious eutrophication were resulted from strong human activities. Therefore, the multi-proxy in Lake Chenghai sediments has reliably recorded the natural environmental evolution and the impacts from human activities.     

Reflectance spectroscopy and geochemical analyses of Lake Hoare sediments, Antarctica: implications for remote sensing of the Earth and Mars

Visible to infrared reflectance spectroscopic analyses (0.3-25 micromoles) have been performed on sediments from the Dry Valleys region of Antarctica. Sample characterization for these sediments includes extensive geochemical analyses and X-ray diffraction (XRD). The reflectance spectra and XRD indicate major amounts of quartz, feldspar, and pyroxene in these samples and lesser amounts of carbonate, mica, chlorite, amphibole, illite, smectite, and organic matter. Calcite is the primary form of carbonate present in these Lake Hoare sediments based on the elemental abundances and spectroscopic features. The particle size distribution of the major and secondary components influences their detection in mixtures and this sensitivity to particle size is manifested differently in the "volume scattering" and "surface scattering" infrared regions. The Christiansen feature lies between these two spectral regimes and is influenced by the spectral properties of both regions. For these mixtures the Christiansen feature was found to be dependent on physical parameters, such as particle size and sample texture, as well as the mineralogy. Semiquantitative spectroscopic detection of calcite and organic material has been tested in these quartz- and feldspar-rich sediments. The relative spectral band depths due to organics and calcite correlate in general with the wt% C from organic matter and carbonate. The amounts of organic matter and carbonate present correlate with high Br and U abundances and high Ca and Sr abundances, respectively. Variation in the elemental abundances was overall minimal, which is consistent with a common sedimentary origin for the forty-two samples studied here from Lake Hoare.     

Geological setting and lithological features of Cenozoic sediments in Ebelyakh Bay (Laptev Sea)

Materials of bottom sampling and drilling on Ebelyakh Bay, the Cape Svyatoi Nos area, and southern part of the Dmitry Laptev Strait by researchers from VNIIOkeangeologiya during the past 60 years and data on the geological setting of the Chokhchur–Chokurdakh zone (Ebelyakh Bay included) were also examined. The geology and lithology of Cenozoic sediments in the water area of the bay and adjacent land were scrutinized to elucidate mineral resources in the Earth’s interior in the study area. Analysis of the Upper Jurassic–Holocene summary section shows that terrigenous material was derived from (i) coastal zones composed of granitoid or contact metamorphic rocks, (ii) Quaternary friable sediments of marine terraces and beaches, (iii) submarine rises, and (iv) river discharge. It is shown that cassiterite is associated with the Pliocene–lower Pleistocene Serkino horizon and Holocene sediments. New promising cassiterite areas have been revealed. The results suggest that prospecting for tin placers should be continued at Ebelyakh Bay.     

Contribution of mineralogical and geochemical data to the study of northeast atlantic deep quaternary sediments: trace-elements as bottom-current indicators

Geochemical and mineralogical study of sixty cores from the northeast Atlantic Ocean used various analyses by X-ray diffraction and fluorescence spectrometry. Thus, we know the clay mineral, carbonate, quartz, feldspar, and trace-element content of the Quaternary sediments from the last interglacial period. These data have been treated in two ways: (1) analysis of the geographical distribution of the components calculated on a carbonate free basis; and (2) statistical analysis establishing the correlation coefficient that exists between the lithological supports and chemical elements.Thus, genetic groups are defined and are correlated to their original sources. For example, smectite-FeTi group is associated with Iceland; feldspar-NiCu with the Faeroe Islands; Illite-Chlorite-RbPb to acidic continental provinces; and SrCaCO₃ to plankton (pàrtially).The lithological supports (smectite, feldspar, carbonate, etc.) are scattered by currents, since chemical elements are associated with them, having a high degree of correlation, it should be possible to utilize these elements as paleohydrologic tracers.     

Isotopic and geochemical characteristics of Upper Cretaceous and Cenozoic flysch sediments of the Kamchatka Peninsula and southern Koryak region

The isotopic and geochemical studies of the Upper Cretaceous-Cenozoic flysch sequences of the Kamchatka Peninsula and southern Koryak region revealed that they were formed at least from two sources: one depleted (T) with low ⁸⁷Sr/⁸⁶Sr and high positive Sr_Nd(T) values and one enriched (T) with high ⁸⁷Sr/⁸⁶Sr and negative Sr_Nd(T) values. The enriched source was likely represented by complexes of ancient upper continental crust. The subduction-related rocks and, to a lesser extent, basalts of mid-oceanic ridges or back-arc basins could serve as a juvenile source for most of the flysch sediments. The Upper Cretaceous flysch sediments differ from their Cenozoic analogues in composition. The Upper Cretaceous rocks are dominated by enriched upper crustal material. The Cenozoic sequences of the Ukelayat Trough and Paleocene-Eocene sequences of the Kumroch Range contain a substantial amount of island-arc volcanoclastic material; the Eocene flysch of Karaginskii Island is compositionally similar to the Upper Cretaceous flysch sequences.     

Lake Teletskoye (Altai,Russia): reconstruction of the environment and prediction for its changes according to the composition and quantity of diatoms in the bottom sediments

We studied the upper 0-1000 mm of the bottom sediment core from the underwater Sofia Lepneva Ridge of Lake Teletskoye. The core sediments accumulated with a rate of 0.3 mm/year (with regard to their humidity, with a rate of 0.45 mm/year) and have an age of about 2000 years. A total of 194 species (212 varieties and forms) of diatoms have been revealed. Analysis of diatom composition in tanatocoenoses showed prevalence of species inhabiting the bottom and periphyton, widely distributed geographically, indifferent to salinity, and preferring a weakly alkaline environment, as well as beta-mesosaprobionts. The number of diatom valves ranged from 0.86 to 64.4 mln valves/g, with an average of 22.90 ± 0.78 mln valves/g. Over the last millennium, the peaks of the abundance of diatoms, especially representatives of the cold-water assemblage, including the main dominant Aulacoseira subarctica (O. Mull.) Haw., are referred to the periods with low water temperature. The pH value for the period from 172 BC to 2006 AD has been reconstructed from the proportion of the numbers of valves of pH-indicating diatom species, which varied from 7.51 to 7.69, with an average of 7.580 ± 0.003. The pH value predicted up to 2259 AD was estimated by spectral (Fourier) analysis at 7.53-7.63, with a similar average of 7.580 ± 0.001. Analysis of reconstructed and predicted pH values showed their insignificant changes and correspondence to a weakly alkaline environment (7.0-8.5). These pH values suggest stability of the lake environment both in the past periods and in the nearest future.     

In-situ formation of perylene in lacustrine sediments and its geochemical significance

Acta Geochimica - To identify the possible sources and formation mechanism of perylene in sediments, temporal trends of perylene and other polycyclic aromatic hydrocarbons, as well as the organic...     

Steroid biological marker hydrocarbons as indicators of organic matter diagenesis in Deep Sea sediments: geochemical reactions and influence of different heat flow regimes

Specific geochemical transformation reactions of steroid hydrocarbons have been chosen to illustrate the molecular evolution of organic matter in deep sea sediments. The progression of isomerisation of (⁵⁴)-sterenes, (20R 20S)-diasterenes, (20R20S)-spirosterenes, and (1414) monoaromatic anthrasteroids with depth has been monitored in core samples from ten DSDP sites. Areas with high geothermal gradients are compared to those with low geothermal heat flow. The formation of regular sterenes and anthrasteroids from functionalized precursors starts close to the sediment/water interface soon after deposition of the organic matter. Due to the high reaction rates these low temperature reactions are independent of the geothermal regime within the limits of sample resolution of this study. In contrast to this, the depth of formation of diasterenes and spirosterenes is dependent on the geothermal gradient. Sedimentation rates indirectly determine, through the effect of the resulting burial depth, the age of the sediments in which these compounds first occur. There is a significant effect of the geothermal gradient on most of the isomerisation reactions studied, and it is most pronounced for the conversion of the 14(H)-B ring monoaromatic anthrasteroids to the 14(H) isomers.

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Zusammenfassung Spezifische geochemische Umwandlungsreaktionen von Steroidkohlenwasserstoffen wurden ausgewählt, um die molekulare Entwicklung des organischen Materials in Tiefseese-dimenten zu illustrieren. Die zunehmende Isomerisierung von (⁵⁴)-Sterenen, (20R20S)-Diasterenen, (20R 20S)-Spirosterenen und (1414)-monoaromatischen Anthrasteroiden mit zunehmender Teufe wurde in Kernproben von zehn DSDP-Bohrlokationen untersucht. Regionen mit hohen geothermischen Gradienten werden solchen mit niedrigem geothermischem Wärmefluß gegenübergestellt. Die Bildung der Sterene und Anthrasteroide aus Vorläufern mit funktionellen Gruppen beginnt bereits in der Nähe der Sediment/Wasser-Grenze kurz nach der Ablagerung des organischen Materials. Wegen der hohen Reaktionsgeschwindigkeiten schon bei niedrigen Temperaturen sind diese Reaktionen innerhalb der für diese Studie zur Verfügung stehenden Probendichte unabhängig vom geothermischen Regime. Im Gegensatz dazu hängt die Bildung der Diasterene und der Spirosterene vom geothermischen Gradienten ab. Über den Einfluß der Versenkungstiefe bestimmt die Sedimentationsrate indirekt das Alter der Sedimente, in denen diese beiden Verbindungsklassen zuerst auftreten. Der Einfluß des geothermischen Gradienten auf die meisten der hier untersuchten Isomerisierungsreaktionen ist erheblich, und er ist am stärksten bei der Umwandlung der 14(H)-B-Ring-monoaromatischen Anthrasteroide in die 14(H)-Isomeren.

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Résumé L'évolution de la matière organique dans les sédiments des grands fonds océaniques est illustrée à l'aide de certaines réactions bien définies de transformation géochimique des stéroïdes. Pour les réactions d'isomérisation du type (⁵⁴)-stérènes, (20R20S)-diastérènes, (20R20S)-spirostérènes et (1414)-anthrastéroïdes aromatiques, la progression en fonction de la profondeur a été étudiée dans une série d'échantillons carottés provenant de dix forages DSDP. Des régions à gradient géothermique élevé sont comparées à d'autres où le flux géothermique est plus faible. La formation des stérènes et anthrastéroïdes réguliers à partir de précurseurs à groupements fonctionnels appropriés débute à proximité de l'interface eau-sédiment peu de temps après le dépôt de la matière organique et progresse assez rapidement même à de basses températures; toutefois le nombre limité d'échantillons disponibles ne permet pas de déceler une influence nette de la situation géothermique. En revanche, la formation des diastérènes et des spirostérènes dépend du gradient géothermique. Puisque la profondeur d'enfouissement augmente avec la vitesse de sédimentation, celle-ci détermine indirectement l'âge des sédiments dans lesquels ces composés apparaissent pour la première fois. La plupart des réactions d'isomérisation étudiées sont sensiblement affectées par le gradient géothermique dont l'influence se manifeste particulièrement pour la transformation des 14(H)-B cyclo-anthrastéroïdes monoaromatiques en leurs 14(H)-analogues.

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, . 10- DSDP (^{5 4})-, (20R 20S)- , (20R 20S)- (14 14)- . . , , /, . .. , , , . . , 14 (H)-B-Ring-oapoaec 14 ()-.

     

大丰市麇鹿自然保护区沉积物元素地球化学特征初探

为研究麋鹿自然保护区的沉积物环境特点,对大丰麋鹿自然保护区一级和三级核心区进行沉积物取样。在实验室中进行了粒度和元素地球化学特点的分析发现,相对于三级核心区,一级核心区因为麋鹿密度的不断扩大以及人类活动的增强,其风化作用比较强烈。另外,缺水严重、人类活动频繁、农业污染等已经影响到沉积物中的元素分布,这种变化有可能会影响到核心区内的植被种类及覆盖情况以及麋鹿饮食的安全。     

Geochronological and geochemical study of mafic dykes from the northwest Chinese Altai: Implications for petrogenesis and tectonic evolution

Fifteen zircons separated from a mafic dyke in the Chinese Altai give a concordant age population with a weighted mean ²⁰⁶Pb/²³⁸U age of 375.5 ± 4.8 Ma, suggesting a Devonian emplacement. On the basis of their mineralogical compositions and textures, the coeval dykes can be divided into gabbroic and doleritic types. They are both sub-alkaline, tholeiitic, characterized by similarly low SiO₂ contents (45.2–52.7 wt.%) and total alkaline (K₂O + Na₂O = 0.99–4.93 wt.%). Rare earth element patterns of the gabbroic dykes are similar to N-MORB (La/Yb_N = 0.86–1.1), together with their high ε_Nd(t) values (+ 7.6 to + 8.1), indicating that their precursor magma was mainly derived from a N-MORB-type depleted asthenospheric mantle. While the REE patterns of the doleritic dykes resemble that of E-MORB (La/Yb_N = 1.12–2.28), enriched in LILEs and strongly depleted in HFSEs, with relative low ε_Nd(t) values (+ 3.4 to + 5.4) and high initial ⁸⁷Sr/⁸⁶Sr ratios (0.7057–0.7060). The zircon Hf isotopic analysis of the doleritic dykes give ε_Hf(t) values from + 10.7 to + 13.8. These signatures suggest that a depleted mantle wedge metasomatized by slab-derived fluids and/or melts was possibly involved in the generation of the doleritic magma. The refractory peridotite may have been melted with variable degrees caused by upwelling of the hot asthenosphere. The petrogenesis of the mafic dykes suggest a high heat flux as a result of upwelling of the hot asthenosphere and the contrast geochemical signatures can be interpreted by a ridge subduction, which could be an important tectonic control in the accretionary process of the Chinese Altai.