A comparative study of n -alkane biomarker and pollen records: an example from southern China

We report the results of a comparative study of n-alkane biomarkers and pollens in lacustrine and peat deposits at Dingnan, Jiangxi Province in southern China, and discuss the likely causes for the discrepancy in the interpretations of the n-alkane biomarker and pollen records in terms of climate and vegetation change. The results show that past changes in climate and vegetation revealed by the n-alkane record are not always consistent with the pollen assemblage record in the whole section. Biomarkers do not permit direct identification of the plant family and/or genus and mainly record compositions of local plant remains, while pollens mainly reflect the regional vegetation change. Biomarkers and pollen records complement each other, providing a better picture of local and regional environments. Furthermore, biomarkers are more sensitive than pollen to climatic and vegetational change. Several climatic events are clearly identified by the n-alkane biomarker proxies, such as C₃₁/(C₂₇+C₂₉+C ₃₁) ratio and can be correlated to the North Atlantic Heinrich event, B/A, YD and two dry-cool events during the early Holocene such as the periods of 9850 to 9585 cal a B.P. and 8590 to 7920 cal a B.P. These events are consistent with those found in the surrounding regions, suggesting that the regional climate was coupled with global-scale abrupt climatic events. Our results suggest that biomarker and pollen data can record the more detailed climate and vegetation information, thus improving the resolution and precision of vegetation and climate reconstruction. Supported by National Natural Science Foundation of China (Grant No. 40602004) and National Basic Research Program of China (Grant No. 2004CB720200)     

Late Cenozoic high-resolution magnetostratigraphy in the Kunlun Pass Basin and its implications for the uplift of the northern Tibetan Plateau

The Kunlun Pass Basin, located in the middle of the eastern Kunlun Mountains, received relatively continuous late Cenozoic sediments from the surrounding mountains, archiving great information to understand the deformation and uplift histories of the northern Tibetan Plateau. The Kunlun-Yellow River Movement, identified from the tectonomorphologic and sedimentary evolution of the Kunlun Pass Basin by Cui Zhijiu et al. （1997, 1998）, is roughly coincident with many important global and Plateau climatic and environmental events, becoming a crucial time interval to understand tectonic-climatic interactions. However, the ages used to constrict the events remain great uncertainty. Here, we present the results of detailed magnetostratigraphy of the late Cenozoic sediments in the Kunlun Pass Basin, which show the basin sediments were formed between about 3.6 Ma and 0.5 Ma and the Kunlun-Yellow River Movement occurred at 1.2 to ～0.78 Ma. The lithology, sedimentary facies and lithofacies associations divide the basin into five stages of tectonosedimentary evolution, indicating the northern Tibetan Plateau having experienced five episodes of tectonic uplifts at ～3.6, 2.69-2.58, 1.77, 1.2, 0.87 and ～0.78 Ma since the Pliocene.     

Magnetostratigraphy of Late Cenozoic fossil mammals in the northeastern margin of the Tibetan Plateau

~~Magnetostratigraphy of Late Cenozoic fossil mammals in the northeastern margin of the Tibetan Plateau~~~~     

天水盆地古近纪地层年代及其意义

天水盆地位于青藏高原东北缘六盘山与西秦岭二重要构造带交汇处,该盆地充填的新生代沉积序列记录着该区构造变形历史,因此研究该盆地沉积记录对探讨青藏高原东北缘新生代构造活动事件具有重要意义.通过对天水盆地古近纪砾石层砂质透镜体中碎屑颗粒磷灰石裂变径迹热年代学研究,获得样品地层的最大沉积年龄为24.8士1.5 Ma.结合前人的工作,厘定该套古近纪地层最顶部地层年龄为22～24.8 Ma,并确定天水盆地古近纪沉积物源区在24.8 Ma左右发生了构造冷却事件,推断印度板块与欧亚大陆碰撞的远程效应在古近纪末-新近纪初已传递到青藏高原的最东北缘.     

Stepwise advance of the Mu Us Desert since late Pliocene: Evidence from a red clay-loess record

Analyses of paleomagnetic polarity reversals, magnetic susceptibility and grain size on the red clay-loess sequence, about 280 m thick, at Jingbian show that this sequence contains most of the stratigraphic units recorded in the standard red clay-loess sections of the Loess Plateau over the past 3.5 Ma. Using sand particle percentage ( > 63 μm%) of the eolian sequence as a proxy indicator of desert extent and aridity in the dust source regions, it is found that during the past 3.5 Ma, there are three important climatic events indicating the advance of the Mu Us Desert. The events occurred at about 2.6, 1.1 and 0.6 MaBP, respectively. The stepwise advance of the Mu Us Desert may be linked closely to increase in global ice volume and uplift of the Tibetan Plateau in the late Cenozoic.     

Carbon isotopic records in paleosols over the Pliocene in Northern China: Implication on vegetation development and Tibetan uplift

Carbon isotopic composition of pedogenic carbonate can be used to estimate the proportion of C₄ and C₃ plants. Here we present carbon isotopic data of carbonate in a red earth section at Xifeng, central Loess Plateau. Results show that C₄ vegetation increased in ∼4.4 Ma B.P., stabilized between 4.0 and 3.0 Ma B.P. The character and timing of C₄ expansion on the Loess Plateau are similar, but different with other localities, e.g. Pakistan and Africa, implying that regional climate changes were main factors driving the expansion of C₄ plants. This event is comparable in timing with increased aridity evidenced by Xifeng grain size and North Pacific eolian dust records. Therefore we argue that the Pliocene expansion of C₄ plants in northern China might have been caused by the increased aridity, which in turn might be related to rapid uplift of the Tibetan Plateau.     

K-Ar age of the Cenozoic volcanic rocks in the Nangqen Basin, Qinghai Province and its geological significance

The Nangqen Basin is one of the typical shearing-extensional basins situated in the north part of the Hengduan Mts. Nine ages of the Cenozoic volcanic rocks from the basin by K-Ar isotope-dilution technique have been reported in the note. The apparent ages of whole rock and separated biotite range from 32.04 to 36.50 Ma. The₄₀Ar-K (%) correlation isochronal line shows that there existed neither argon excessing, nor radiogenetic argon loosing, i.e. the age represents the true diagenetic time. Volcanic activity in this area occurred in the post-collision environment and is controlled by lithosphere substantial thickening and violent intercontinental shearing-strike slip faults. There is age difference of the magmatic activity in the east, the west and the north Tibet. The multi-periodic eruption-intrusion of the magmatic melt since Cenozoic is a tracer showing the pulsating uplift of the Tibetan Plateau.     

青藏高原东南部地貌边界带晚新生代构造运动

青藏高原是中国大陆最高一级地貌阶梯,其东南部地貌边界大致沿龙门山—大相岭—锦屏山—玉龙山—碧罗雪山一线分布。该文主要从青藏高原东南部地貌边界两侧的晚新生代地层记录来探讨晚新生代构造运动以及高原隆升。青藏高原东南部地貌边界带雏形出现于距今２．５Ｍａ左右,定型于１．２Ｍａ前的构造运动中,之后又在构造运动进程中不断得到加强,并最终形成今日之构造地貌格局。青藏高原从海变陆,并上升至平均海拔４５００ｍ以上,成为地球上最高的大高原,这是发生在晚新生代且主要是在第四纪最重大的地质事件。     

青藏高原隆升阶段性

 青藏高原的隆升不仅是印度板块与亚洲板块碰撞导致的地球内部岩石圈地球动力学作用过程的结果,并且对全球和亚洲气候变化、亚洲地貌和地表环境过程及大量地内和地表矿产资源的形成分布产生了深刻影响。因而研究高原隆升的历史不仅对解决上述重大科学问题提供重要途径,而且可为高原区域资源环境的开发和可持续发展提供理论依据。简要回顾和梳理了国内外近年来,围绕青藏高原隆升所取得的主要进展。研究表明新生代青藏高原经历了多阶段、多幕次、准同步异幅且高原南北后期加速隆升的演化过程。具体可划分为55~30、25~10及8~0 Ma 3个主要生长隆升期次。其中55~30 Ma的高原早期隆升,主要集中在高原中南部的拉萨地块和羌塘地块,并且可能隆升到接近3 km高度,或甚至更高,有人称之为“原西藏高原”,但其周缘存在准同步异幅的变形隆升响应;25~10 Ma的中期隆升,“原西藏高原”南北缘的喜马拉雅山和可可西里-昆仑山开始强烈隆升,“原西藏高原”率先隆升到目前高度并开始向东西两侧挤出物质、拉张形成南北向裂谷,高原北缘普遍产生广泛变形隆升但幅度有限;从约8 Ma开始的晚期隆升,高原南、北部边缘的喜马拉雅山和昆仑山-西秦岭以北的高原东北部隆升显著加速,经历一系列短暂快速的多幕次构造变形和生长隆升,最终形成现今高原面貌。     

青藏高原：全球气候变化的驱动机与放大器──Ⅰ 新生代气候变化的基本特征

除周期性气候波动外，新生代气候变化的基本特征是阶梯状气候变冷、波动幅度的不断增加和气候波动周期的转变。深海氧同位素记录表明新生代曾发生至少三次快速变冷事件，它们分别发生在３６，１５和２．４ＭａＢＰ前后。根据来自北大西洋的深海氧同位素记录，第四纪气候变化的趋势是波动幅度增加、频率降低。Ｂ／Ｍ界限附近，气候波动周期由４１ｋａ转变为１００ｋａ。黄土高原上黄土地层与磁化率研究揭示，现代东亚季风出现于２．４Ｍａ前，并于１．１和０．６ＭａＢＰ前后两度加强，现在的季风环流形势形成于０．６ＭａＢＰ，米兰柯维奇理论不能解释上述新生代气候的阶梯状变冷、第四纪气候的阶段性和东亚季风的形成及加强，因此除轨道因素外，还有别的因素控制气候变化。     

Uplift of the Tibetan Plateau and environmental changes

Major progress, problems, and challenges of recent investigation of the Tibetan Plateau uplift processes and resulting environmental changes are reviewed and summarized briefly, which especially covers the National Tibetan Research Projects of the Chinese Eighth (1992-1996) and Ninth (1997-2001) "Five-Year Projects". The Tibetan Plateau uplift is a complicated multiple cyclic process. The Gangdise and Himalayas began to uplift in the Middle Eocene and Early Miocene respectively, while the main part of the Plateau merely underwent corresponding passive deformation and secular denudation, resulting in two planation surfaces. The third and also the strongest uplift involved the whole Plateau and its marginal mountains commenced at 3.6 Ma. Successive Kunlun-Huanghe movement at 1.1-0.6 Ma and Gonghe movement at 0.15 Ma raised the Plateau to its present height. The Asian monsoonal system and Asian natural environment formed in response to these tectonic uplifts.     

Magneto-and pedo-stratigraphy of paleosol-loess sequences in the Lanzhou Basin:Evidence for evolution of Huang He

Results of magnetopedostratigraphic study of three sections of loess in the Lanzhou Basin are significant. (1) The oldest aeolian loess deposited on pediment in the Lanzhou Basin dates back to 1.8 Ma, indicating the end of erosion development. (2) The highest (also oldest) terrace T7 is identified and dated at about 1.7 Ma. Huang He began developing (about 1.8-1.7 Ma) after dissection of the pediment and before the oldest terrace formed. The incision rate of Huang He varied with time. Its two peak periods are from 1.8 to 1.7 Ma BP and from 0.15 Ma BP to present, corresponding to episodic uplift of the Tibetan Plateau.     

Influence of the Tibetan Plateau uplift on the Asian monsoon-arid environment evolution

As one of the most important geological events in Cenozoic era,the uplift of the Tibetan Plateau(TP)has had profound influences on the Asian and global climate and environment evolution.During the past four decades,many scholars from China and abroad have studied climatic and environmental effects of the TP uplift by using a variety of geological records and paleoclimate numerical simulations.The existing research results enrich our understanding of the mechanisms of Asian monsoon changes and interior aridification,but so far there are still a lot of issues that need to be thought deeply and investigated further.This paper attempts to review the research on the influence of the TP uplift on the Asian monsoon-arid environment,summarize three types of numerical simulations including bulk-plateau uplift,phased uplift and sub-regional uplift,and especially to analyze regional differences in responses of climate and environment to different forms of tectonic uplifts.From previous modeling results,the land-sea distribution and the Himalayan uplift may have a large effect in the establishment and development of the South Asian monsoon.However,the formation and evolution of the monsoon in northern East Asia,the intensified dryness north of the TP and enhanced Asian dust cycle may be more closely related to the uplift of the main body,especially the northern part of the TP.In this review,we also discuss relative roles of the TP uplift and other impact factors,origins of the South Asian monsoon and East Asian monsoon,feedback effects and nonlinear responses of climatic and environmental changes to the plateau uplift.Finally,we make comparisons between numerical simulations and geological records,discuss their uncertainties,and highlight some problems worthy of further studying.     

青藏高原地面抬升证据讨论

当前学术界在青藏高原地面何时达到现代高度问题上存在着许多不同观点,概括起来主要有３种：１４Ｍａ前已达到高于现代的最大高度,８Ｍａ前已达到或超过现代高度,距今３．４Ｍａ来分阶中强烈上升并逐步达到现代高度,之所以出现如此大的意见分歧,除高原面积广阔,研究程度不深和覆盖面不够的原因外,不同研究者所使用研究方法和证据的差异也是重要因素,在分析了各种证据对高原地面上升的记录机理后,我们认为夷平面、河流附地,     

Evidence for cold events in the early Holocene from the Guliya ice core, Tibetan Plateau, China

Evidence for the “8.2 ka cold event” has been provided mostly from the circum-North Atlantic area. However, whether this cold event occurred in other places is a key to understanding its cause. Here, we provide the evidence for the “8.2 ka cold event” from the Guliya ice core in the northwest Tibetan Plateau, and it was found that the peak cooling (~8.3—8.2 ka) in this ice core was about 7.8—10℃, which was larger than the cooling in the North Atlantic region. The primary causes for this episode were diminished solar activity and weakened thermohaline circulation. Moreover, another weak cold event, centered about 9.4 ka, was also recorded in the Guliya ice core record. These two cold events were concurrent with the ice-rafting episodes in the North Atlantic during the early Holocene, which implies that the millennial-scale climatic cyclicity might exist in the Tibetan Plateau as well as in the North Atlantic.     

Climatic and environmental implications from n-alkanes in glacially eroded lake sediments in Tibetan Plateau: An example from Ximen Co

Gas chromatography-mass spectrometry was used to identify a series of n-alkanes in the sediments of a typical glacially eroded lake in the eastern Tibetan Plateau.By comparing the distribution patterns of n-alkanes in lake sediments,surface soils and cow manure,it was shown that n-C 27-n-C 33 alkanes in the soil ecosystem of Ximen Co are derived from vascular plant species and that the distribution pattern of n-C 27-n-C 33 alkanes remains unchanged during the feeding and digestion processes of herbivores.The relative percentage of C 27,C 29 and C 31 n-alkanes decreased from the bottom to the top of the sediment core showing a trend of degradation of higher plants in the Ximen Co lake region during the formation of the 44 cm core.210 Pb dating,combined with pre-existing AMS 14 C dating results showed that the depositional core reflects climatic and environmental variations since about 900 years before present.The n-alkane indexes (ACL 27-33,P aq,P wax) are comparable with regional temperature variation,especially recording the Little Ice Age event (LIA).This study highlights that n-alkanes are valid proxies for paleo-climate and paleo-environment reconstruction,despite the same distribution patterns in n-alkane molecular fossils derived from a typical glacially eroded lake.     

Molecular phylogeny and biogeography of the highly specialized grade schizothoracine fishes （Teleostei： Cyprinidae） inferred from cytochrome b sequences

We recovered the phylogenetic relationships among 23 species and subspecies of the highly special-ized grade schizothoracine fishes distributing at 36 geographical sites in the Tibetan Plateau and its surrounding regions by analyzing sequences of cytochrome b genes. Furthermore, we estimated the possible divergent times among lineages based on a historical geological isolation event in the Tibetan Plateau. The molecular data revealed that the highly specialized grade schizothoracine fishes were not a monophyletic group, but were the same as genera Gymnocypris and Schizogypsis. Our results indi-cated that the molecular phylogenetic relationships apparently reflected their geographical and historical associations with drainages, namely species from the same and adjacent drainages clustered together and had close relationships. The divergence times of different lineages were well consistent with the rapid uplift phases of the Tibetan Plateau in the late Cenozoic, suggesting that the origin and evolution of schizothoracine fishes were strongly influenced by environment changes resulting from the upheaval of the Tibetan Plateau.     

Millennial-scale climate change since the last glaciation recorded by grain sizes of loess deposits on the northeastern Tibetan Plateau

Whether climatic changes in high latitudes of the Northern Hemisphere since the last glaciation have effects on the Tibetan Plateau monsoon, and the variation characteristics of the Plateau monsoon itself are still not solved but of great significance. The 22-m high-resolution Ioess-paleosol sequence in the Hezuo Basin on the northeastern Tibetan Plateau demonstrates that the Plateau winter monsoon experienced a millennial variation similar to high latitude Northern Hemisphere, with cold events clearly correlated with Heinrich events but less for the warm events (Dansgarrd-Oeschger events). It may indicate that the climate system at high latitudes in the Northern Hemisphere had played an important role in both the Plateau monsoon and the high-level westerlies. On 10^4 year scale, there are two distinct anomalous changes, which are not found in the records from high latitude northern hemisphere, revealed by the loess grain size in the Hezuo Basin. One is that there was a considerable grain size increase at -36 kaBP, suggesting an abrupt enhancement of the Plateau winter monsoon at that time; the other is that, during 43--36 kaBP, the grain size decreased distinctly, indicating a notable weakening of the Plateau winter monsoon around that period. Both of the two anomalies suggest that the Tibetan climate may have been controlled by some other factors, besides the high latitude climatic changes in the Northern Hemisphere.     

Tibetan plateau aridification linked to global cooling at the Eocene-Oligocene transition

Continental aridification and the intensification of the monsoons in Asia are generally attributed to uplift of the Tibetan plateau and to the land-sea redistributions associated with the continental collision of India and Asia, whereas some studies suggest that past changes in Asian environments are mainly governed by global climate. The most dramatic climate event since the onset of the collision of India and Asia is the Eocene-Oligocene transition, an abrupt cooling step associated with the onset of glaciation in Antarctica 34 million years ago. However, the influence of this global event on Asian environments is poorly understood. Here we use magnetostratigraphy and cyclostratigraphy to show that aridification, which is indicated by the disappearance of playa lake deposits in the northeastern Tibetan plateau, occurred precisely at the time of the Eocene-Oligocene transition. Our findings suggest that this global transition is linked to significant aridification and cooling in continental Asia recorded by palaeontological and palaeoenvironmental changes, and thus support the idea that global cooling is associated with the Eocene-Oligocene transition. We show that, with sufficient age control on the sedimentary records, global climate can be distinguished from tectonism and recognized as a major contributor to continental Asian environments.     

Magnetostratigraphy of Late Tertiary sediments from the Chinese Loess Plateau and its paleoclimatic significance

The Late Tertiary red clay/bed sediments underlying the Quaternary loess-paleosol in the Chinese Loess Plateau possesses high-resolution paleoclimatic changes related to the uplift of the Tibetan Plateau. Magnetostratigra-phy and susceptibility measurements are discussed in this paper. The paleomagnetic results show that the red clay/bed began to accumulate at about 8.1 Ma, which represents the oldest Late Tertiary deposit continuously in the central Loess Plateau. The magnetic susceptibility curves show stepwise increases since the initiation of red clay, superimposed on several peaks. Moreover, the magnetic susceptibility increased abruptly since 3.8 Ma, which probably indicates the inception of the modern East Asia monsoon system. Between 3.8 and 2.6 Ma, the stepwise increases of susceptibility may imply progressively intensified East Asia summer monsoon activity related with the stepwise uplift process of the Tibetan Plateau.