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.     

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~~~~     

由黄河阶地变形反映的兰州盆地活动构造特征

通过大比例尺航空照片、1:10 000地形图及DEM图像研究和详细的野外调查,确定了兰州盆地各级阶地的分布状况.野外利用差分GPS实地测量了各级阶地海拔高度,据此得到了兰州盆地黄河两岸阶地纵剖面图.根据剖面图中阶地变形特点分析了兰州盆地活动构造特征,发现兰州盆地内活动构造以褶皱变形为主,断层多为褶皱隆起过程中的派生断裂,其活动性较弱.兰州盆地内变形的动力来源于西南方向马衔山北缘断层的左旋走滑.现有的地质资料也支持了这种观点.     

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.     

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.     

柴达木盆地西部第三系碳酸盐岩层的古生物特征

柴达木盆地西部第三系的碳酸盐岩层中发现有藻类、介形虫、有孔虫、腹足类、多毛类等化石.除藻类外各种生物的数量都比较少.生物具有个体小,壳体构造简单,多样性低等特点.所有生物都属于广盐性生物.根据该区古生物特征分析和与其它地区的对比,认为当时该区生物生长于内陆半咸化湖至咸化湖环境,而不是海相或海陆过渡相环境.参11.     

柴达木盆地第三纪盐湖沉积环境分析

目的分析柴达木盆地第三纪盐湖的沉积环境。方法利用稳定同位素分馏理论及其分析技术，分析了现代青海湖稳定同位素的组成特征，并与柴达木盆地第三纪盐湖的沉积环境特点进行了对比。结果柴达木盆地第三纪咸化湖泊沉积碳酸盐岩中富集δ13C与δ18O，具有较高的Z值，并且大多与海洋碳酸盐岩碳氧同位素区间值重叠，说明第三纪咸化湖泊的盐度与海相相当或高于海水；柴达木盆地硫酸盐的δ34值大大超过海洋硫酸盐的δ34S值，且在第三纪盐湖的演化过程中具有化学分层特征，在湖盆下部产生了强烈的硫同位素分馏现象，导致较高δ34S值蒸发岩沉积的形成。结论柴达木盆地第三系盐湖沉积地层中可发育较丰富的油气资源。     

Palaeogene fossil <Emphasis Type="Italic">Populus</Emphasis> leaves from Lanzhou Basin and their palaeoclimatic significance

An angiosperm compression flora is found in Palaeogene from Lanzhou Basin and the cuticular analysis of Populus davidiana Dode in the flora is carefully made. Furthermore, the fossil cuticles are compared with the epidermal structures of extant Populus leaves growing in different environments, i.e. moist, semimoist, and semiarid to arid climatic regions. The present experiments indicate that mature leaves of P. davidiana show leaf size from big to small, leaf cuticles from thick to thin and anticlinal walls of epidermal cells from faintness to clarity along with the increase of lattudes of the plant distributions, the climatic variation from moist to arid, the annual precipitation from more to less and the annual mean temperature from high to low. The fossil P. davidiana differs from the specimens collected from Shandan in semiarid to arid climatic regions but closely resembles the Wushan leaves in a semi-moist climatic area in a lot of features. In a word, the new research may reflect that the flora lives in a semi-moist climatic environment. The present discovery of compression of Paleogene Populus davidiana is of great significance to studying vegetation types, climatic and environmental changes during the primal uplifting of the Qinghai-Tibet Plateau.     

柴达木盆地北缘第三系沉积体系演化模式

基于柴达木盆地北缘第三系的地质背景和构造演化,结合野外露头、岩心、测井解释和地震相特征,研究了沉积相的纵横分布特征并建立了柴北缘第三系沉积体系演化模式。结果表明:盆地边缘的马北、马西和平台地区一带主要以冲积扇和辫状河沉积为主,靠近湖盆中心的南八仙、冷湖Ⅵ号和Ⅶ号、鄂博梁等地区主要发育辫状河三角洲平原或前缘相带。路乐河组(E1+2)冲积扇较为发育,辫状河相对发育;下干柴沟组(E3)主要发育辫状河和辫状河三角洲沉积,下干柴沟组下段(E13)到下干柴沟组上段(E23)是一个辫状河向辫状河三角洲演化的水进沉积序列;上干柴沟组(N1)和油砂山组(N2)发生进一步湖侵,湖盆扩张,为辫状河三角洲前缘与滨浅湖的交互沉积。在此基础上,建立了柴北缘古近纪—新近纪从物源区向盆地中心发育的冲积扇—辫状河—辫状河三角洲—湖泊沉积体系模式,并探讨了沉积体系演化过程及其油气意义。     

A tropical paleosol at high elevation in the Yulong Mountains and its implication on the uplift of the Tibetan Plateau

A paleosol dated for about 500–700 kaBP and developed on a glacial deposit at ～3 000 m a.s.l. in the Yulong Mountains is studied using soil chemical, morphological and mineralogical methods. The analytical results indicate that this soil was formed under tropical and humid conditions and can be classified as red soil, which cannot be formed in the present alpine environment at the studied site. This implies that the southeast margin of the Tibetan Plateau has experienced intense uplift since the formation of the paleosol. According to the necessary conditions for the formation of the modern red soil in China, we estimate that the uplift height of the Plateau since 500–700 kaBP would have exceeded 800 m.     

柴达木盆地西部地区第三系碎屑岩粒度概率累积曲线特征

在岩心观察的基础上，利用主要取心井的粒度分析资料，对柴达木盆地西部地区第三系碎屑岩主要沉积环境的粒度概率曲线进行了研究。研究表明，该地区发育的沉积相有扇三角洲、冲积平原、三角洲、湖泊、湖底扇，每一种沉积相又分为几种沉积亚相类型；该地区碎屑岩的粒度概率累积曲线特征主要包括：“上拱弧形”式、一段式、两段式、三段式、多段式、复杂两段式和复杂三段式、“低斜多段”式、“高斜多跳-悬”式和“高斜多跳-悬夹过渡”式、“高斜多跳”式、“宽缓上拱”式等，每种沉积亚相类型对应其独特的粒度概率累积曲线特征。该研究成果可为新探区的沉积环境判断提供参考。     

准噶尔盆地南缘古近系-新近系异常高压系统与油气成藏机理

运用钻井压力监测、电缆测试实测压力和声波时差等资料 ,对准噶尔盆地南缘古近系新近系中普遍存在的异常高压地层进行了识别。研究结果表明 ,研究区存在滞排型和顶封滞排型两种异常高压系统 ,其中欠压实作用、封隔层封闭作用和构造抬升作用是异常高压系统的主要成因 ;同时认为异常高压对该地区油气成藏具有控制作用。准噶尔盆地南缘呼图壁地区的滞排型异常高压系统有益于气藏的形成和保存 ;独山子异常高压系统只对超压系统形成之前和同期运移来的油气起封隔和保存作用 ,而对后期的油气向系统内运移起阻止作用 ,从而影响油气聚集     

Northern Tibetan Plateau cooling and aridification linked to Cenozoic global cooling: Evidence from <Emphasis Type="Italic">n</Emphasis>-alkane distributions of Paleogene sedimentary sequences in the Xining Basin

The Xining Basin on the northeastern Tibetan Plateau holds the longest continuous Cenozoic stratigraphic record in China. The sequence record contains considerable information on the history of Tibetan uplift and associated climatic change. In particular, high resolution n-alkane biomarker proxy and pollen records have been obtained from the Paleogene sediments of the Xiejia section of the basin. A combination of the n-alkane and palynological records reveals that the paleoclimate in the Xining Basin experienced a long-term cooling trend from 50.2 to 28.2 Ma with a distinctive ecological event spanning 37.5 to 32.7 Ma. Since this ecological event, a vertical zonation of vegetation from lowland arid grasses, to middle-elevation subtropical broad-leaf plants, to high-elevation coniferous trees was established. We interpret that these changes in climate and vegetation were probably responses to a combination of long term global cooling since the Eocene climatic optimum and uplift of the surrounding mountains on the northern Tibetan Plateau in the early Cenozoic.     

柴达木盆地西部地区第三系碎屑岩粒度概率累积曲线特征

在岩心观察的基础上,利用主要取心井的粒度分析资料,对柴达木盆地西部地区第三系碎屑岩主要沉积环境的粒度概率曲线进行了研究。研究表明,该地区发育的沉积相有扇三角洲、冲积平原、三角洲、湖泊、湖底扇,每一种沉积相又分为几种沉积亚相类型;该地区碎屑岩的粒度概率累积曲线特征主要包括:“上拱弧形”式、一段式、两段式、三段式、多段式、复杂两段式和复杂三段式、“低斜多段”式、“高斜多跳一悬”式和“高斜多跳一悬夹过渡”式、“高斜多跳”式、“宽缓上拱”式等,每种沉积亚相类型对应其独特的粒度概率累积曲线特征。该研究成果可为新探区的沉积环境判断提供参考。     

Recent Advances in the Small Mammal Biostratigraphy and Magnetostratigraphy of Lanzhou Basin

The consensus view among geologists is that the Lanzhou Basin sequence of sediments contains the Oligocene/Miocene boundary, but where this occurs is unknown. Indeed, this is the crux of the issues concerning mid-Tertiary paleontology in Asia: what fauna corresponds with this time? What turnover events or distinctive taxa signal the beginning of the Miocene epoch? Once known, this will be of broad usefulness because vertebrate-bearing deposits are widespread in Asia and can be used to date basin sediments. Lanzhou and other basins permit a means of correlating to the time scale by using fauna and paleomagnetic data locally, and ultimately radiometric data from distant localities, to develop a precise biochronology. Herein, we summarize faunal constraints, primarily those of small mammal taxa, on correlation of the Lanzhou magnetozone sequence to the magnetic time scale. We conclude that the lower part of the Xianshuihe Formation contains the Oligocene/Miocene boundary, and that the top of the formation, both in the south and north parts of the basin, is middle Miocene in age. Rodents from lower white sand units of the Xianshuihe Formation, correlate to the Xiejia assemblage of the Xining Basin, Qinghai Province, and are early, but not earliest, Miocene age. The implication for rodent faunas of the epoch boundary is that they retained a mainly "Oligocene" composition, and that other presumed late Oligocene assemblages may be, in fact, early Miocene in age. The Lanzhou appearance of Proboscidea is 19-18 Ma, as expected.     

柴达木盆地第三纪湖盆古水介质研究

根据大量分析化验资料对柴达木盆地第三纪湖盆古水介质的演化进行了研究 .第三纪湖盆微量元素特征表现为微咸水 -咸水 ,并且在湖盆演化的不同时期其古水介质条件有明显的变化 .碳酸盐岩、膏盐、盐岩组合以及生物标志化合物组合在垂向上的变化反映出第三纪经历了两次盐湖旋回的演化 ,并且这种盐湖演化同第三纪湖盆沉积中心、沉降中心的迁移是一致的 .在盐湖盆地沉积中粘土矿物呈现正常型和非正常型两种演化模式 .     

洞庭盆地全新世古环境研究现状

在总结与分析前人研究工作的基础上,提出目前洞庭盆地全新世古环境研究存在的主要问题,并提出了今后的努力方向。目前,对洞庭盆地全新世古环境演化特征的认识还是比较浅薄的,存在的主要问题包括：1）未进行详细的全新统地层划分与对比;2）缺乏多指标约束;3）时间分辨率很低;4）未进行定量古环境研究。今后努力方向主要包括：1）建立精细的全新统年代地层框架;2）加强对微体古生物古环境意义的研究;3）采用高分辨率岩心取样方法;4）进一步加强考古研究工作。     

柴达木盆地第三系碎屑岩中粘土矿物特征及储层保护措施

柴达木盆地第三系碎屑岩中粘土矿物含量较低,一般小于４％大多数介于１％－２％,故对也孔隙度影响不明显,经Ｘ射线衍射分析可知,粘土矿物主要有４大类：伊／蒙混层粘土,伊利石,绿泥石和高岭石。它们的相对含量及形态产状,对不同地区不同层位的储层有着不同的潜在危害。     

青藏高原东北缘临夏盆地王家山地区沉积环境分析与构造隆升

通过对青藏高原东北缘临夏盆地王家山地区新生代地层沉积相研究，划分出7个沉积旋回；盆地沉积与高原隆升的响应关系揭示出高原29Ma以来先后经历了初期隆升至稳定阶段(29．0—21．4Ma)、中期随升至稳定阶段(21．4—6．25Ma)、后期逐步隆升阶段(6．25—3．58Ma)和晚期急剧强烈隆升阶段(3．58—0Ma)，可见青藏高原的隆升是一个多阶段、不等速和非均变的复杂过程．     

Two coldhumid climatic events record in the early Pleistocene deposits of the Linxia Basin

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