云南剑川盆地古近纪沙漠沉积特征和古风向重建

气候模拟显示,中国在古近纪曾被带状干旱带控制并被大面积沙漠沉积覆盖,然而在中国境内,尤其是在青藏高原周边气候变化与青藏高原隆升耦合敏感地区却鲜有发现,一定程度制约了东亚季风起源时间和气候变化研究。本文通过岩性、沉积结构、沉积构造、石英砂颗粒表面特征、铁质黏土套的化学成分特征和风成沙丘分布面积综合分析,证实了剑川盆地古近系始新统宝相寺组中段典型沙漠沉积的存在。古风向重建显示,沙漠早期为西风控制,晚期为西北风控制并伴随有初始季风雨。综合分析区域地质证据可见,青藏高原东缘始新世中晚期经历了一个由干旱到潮湿的气候剧变事件,而沙漠的消失即为该事件的标志。研究区古近纪风向偏转、初始季风雨的出现以及沙漠的消失表明,东亚季风可能始于晚始新世。本文进一步确证了青藏高原东缘古近纪沙漠的存在,对深化研究东亚季风起源的时间及其与青藏高原隆升的耦合关系具重要意义。     

青藏高原东缘盐源盆地古近纪风成沙丘及其古地理意义*

盐源盆地始新世丽江组沉积时期发育了一套具大型高角度交错层理的红色砂岩,其确切成因对于厘定青藏高原东缘古近纪古地理格局、恢复东亚新生代干旱带与古气候演化过程具有重要意义。文中通过对盐源盆地始新统丽江组红色砂岩的沉积特征进行系统分析,证明该套砂岩的岩性、粒度分布、石英颗粒表面特征与沉积构造等明显不同于水成沉积,而与典型风成沙丘相应特征完全一致,表明其为风成沙丘沉积。结合古近纪研究区的古气候条件、大气环流样式与大地构造背景,笔者进一步推断盐源盆地始新世风成沙丘可能沉积于中国古近纪干旱带内的沙漠环境。根据目前相关研究资料,确认青藏高原东缘存在一个厚度稳定的古近纪风成沙丘富集带。     

四川盆地古近纪古风向恢复与大气环流样式重建

四川盆地白垩纪—古近纪发育了大量沙漠沉积,是恢复古风向与重建大气环流样式的宝贵证据.通过对四川盆地古近纪柳嘉组大型风成沙丘前积层倾向的系统测量,参照当时的古纬度、古方位及大气环流模式,恢复了四川盆地古近纪的古风向,重建了当时的大气环流样式.结果表明,四川盆地古近纪盛行西风,受西风带控制.结合前人的研究成果可以得出,四川盆地白垩纪早期由东北信风带控制,晚期由西风带控制,古近纪早期则继承了白垩纪晚期的大气环流样式,仍由西风带控制,其大气环流样式的转换大约发生在晚白垩世中期,至少在古近纪柳嘉组沉积时期,东亚季风尚未建立,四川盆地仍为行星环流控制.     

青藏高原东缘近2000年湖泊气候记录及全球联系

青藏高原东缘气候变化历史对认识区域乃至全球气候动力成因有重要意义。本文基于笔者近年来在青藏高原东缘获取的湖泊记录,并汇总他人研究成果,探讨了高原东缘近2000年气候变化历史。已有的研究表明青藏高原东缘北部(NETP)和南部(S-ETP)近2000年水文气候存在显著的区域差异。N-ETP地区中世纪总体温暖湿润,小冰期寒冷干燥,近100~200年温暖湿润,表现为"暖湿-冷干"气候模式;而S-ETP地区中世纪温暖干旱,小冰期寒冷湿润,近100~200年温暖干旱,表现为"冷湿-暖干"气候模式。对比分析表明:N-ETP地区气候模式与东亚夏季风广泛区域气候模式相似;而S-ETP地区气候模式与多数印度夏季风地区气候模式相似。因而认为这样大尺度的水文气候差异可能与不同区域大气环流差异以及赤道太平洋-印度洋海表面温度变化及其引起的大气环流的强度及位置的变化有关。     

青海共和盆地早全新世古风向重建及其对黄土物源的指示

青藏高原东北部地处黄土与沙漠的过渡地区,在冰期-间冰期旋回中受中纬西风与东亚季风环流的交替控制,曾发生大范围的沙漠进退,是黄土高原重要的潜在物源区。恢复该区地质历史时期的大气环流格局可为重建东亚地区的环境面貌、探讨黄土高原的物源区、检验东亚地区古气候模拟结果的有效性等方面提供重要依据。但目前对高原东北部的古大气环流特征却鲜有研究。青藏高原东北部保存有一系列的古沙丘,可为古大气环流的重建提供直接依据。本文选取青海共和盆地一处代表性新月形古沙丘开展光释光测年研究,并通过其平面形态和前积层产状恢复了当时的古风向。结果表明:共和盆地的风沙活动自早全新世以来开始显著减弱,此时近地面盛行与现今风向一致的西北风。前人的研究揭示出青藏高原东北部在冰期时很可能盛行西风,并存在广泛的荒漠化,因而很可能是黄土高原冰期时重要的物源区之一。而本研究指示,该区的盛行风向在早全新世以来转变为西北风,且荒漠范围显著退缩,导致其全新世不再是黄土高原的物源区。青藏高原东北部的盛行风向和荒漠范围在冰期-间冰期旋回中的这种变化,为理解黄土高原的粉尘物源在空间和冰期-间冰期旋回上的变化提供了依据。     

青藏高原东缘古近纪粗碎屑岩沉积学及其构造意义

青藏高原东缘古近纪盆地的填图和沉积学研究表明,在青藏高原东缘区域性走滑-挤压构造背景下形成的古近纪盆地内广泛发育厚层—巨厚层状的紫红色粗碎屑岩系。其沉积特征指示为一种近源快速堆积的泥石流和辫状河道沉积体,形成于干旱炎热气候条件下的典型陆内冲积扇环境。盆地充填序列、粗碎屑岩层序、动植物化石和盆地内岩浆岩~(40)Ar-~(39)Ar年代学等综合研究结果表明,古近纪盆地内粗碎屑岩大约形成于38～29 Ma。该时期与青藏高原东缘北段(横断山地区)古近纪盆地的形成和南段(兰坪—思茅地区)大盆地的裂解时间基本一致,这很可能预示着青藏高原在晚始新世—早渐新世期间曾发生过整体的快速构造隆升。     

青藏高原渐新世晚期隆升的地质证据

国内外学者普遍认为,地壳缩短增厚是青藏高原隆升的主要原因,青藏高原隆升对环境变迁和东亚季风具有重要影响,但对青藏高原隆升时代存在不同认识。通过统计分析青藏高原中段新生代不同时期的地层倾角,表明区域褶皱变形主要发生于古近纪,中新世湖相沉积地层产状平缓,挤压构造变形微弱,说明地壳缩短增厚主要发生于中新世前。湖相沉积地层的孢粉分析结果表明,青藏地区热带亚热带阔叶林植被自始新世中期开始逐步减少,至中新世早期濒临消亡;暗针叶林植被自渐新世早中期开始逐步增加,至中新世早中期达到繁盛程度甚至居主导地位。根据这些地质证据,结合全球气候变化、古气温及年代学资料,综合推断青藏高原渐新世晚期隆升高度达到海拔4000m左右。     

东亚东倾地形格局的形成与季风系统演化历史寻踪——综合大洋钻探计划683号航次建议书简介

围绕IODP 683号建议书,介绍东亚东倾地形格局与季风系统演化历史的相关研究。新生代全球宏观环境格局发生了一系列重大变化,表现为岩石圈活动强烈,板块漂移导致海陆格局和地貌格局的变化,并引发洋流和大气环流的改组,最终导致全球气候的重大变化。新生代岩石圈运动和气候变化表现最为典型的地区是亚洲,其中最具标志性和全球意义的地质事件是喜马拉雅山和青藏高原的隆升及亚洲季风系统的形成与演化。青藏高原隆升最直接的结果是亚洲地区现代地貌格局的形成,大江大河的发育,并在很大程度上影响了亚洲季风系统的形成与演化。综合大洋钻探计划683号航次建议书,计划在长江中下游盆地和东海陆架盆地实施钻探,以获得长江历史演化和东亚季风演化的地质记录,并为研究青藏高原的演化提供新的证据。     

六盘山北部寺口子砂岩研究现状、问题及意义

古近纪内陆古环境重建是我国第四纪和新生代地质研究面临的前沿课题。位于青藏高原东北缘六盘山北部,作为著名寺口子组的正层型剖面,寺口子砂岩剖面是该期内陆环境变化重建的一个理想剖面。但其成因认识尚存在水成与风成两大分歧,以致其时代、成因、环境等一系列问题尚无定论。前人研究的基础上,通过对寺口子剖面进行野外调查与研究,进一步厘定沉积时代,澄清沉积特征,揭示成因类型,恢复沉积过程,重建其古地理环境与演变过程,并与区域及全球有关地质环境及古气候事件记录进行对比,探讨其对全球气候环境演变的响应机理,有助于解决该地层的成因与环境问题,有望建立一个典型古近纪内陆沉积剖面,促进中国内陆古近系记录及其古环境研究,并为青藏高原隆升—季风变迁—沙漠演化等耦合机制研究提供新的证据,同时,对类似砂岩地层的研究具有一定的推动作用。     

巴丹吉林沙漠全新世环境记录的年代校正与古气候重建

巴丹吉林沙漠地处东亚夏季风区的西北缘,是认识东亚季风演变及其区域响应的窗口.文章在系统研究前人工作的基础上,对环境记录的年代进行了新的校正,并重建了全新世环境演变的历史.分析结果显示,巴丹吉林沙漠在早全新世开始出现高湖面,早中全新世在湖区广泛出现高湖面和淡水环境并在沙漠东北缘发育了古土壤,晚全新世时湖泊水位下降,沉积地层以风成砂为主.巴丹吉林沙漠全新世环境变化总体上可分为3个阶段:晚更新世末至早全新世初气候干旱;在10.0cal.kaB.P.左右气候由干向湿快速变化,并在8.5～4.0cal.kaB.P.期间气候最为湿润,但同时存在短期的十湿波动;4.0cal.kaB.P.以来气候总体干旱,但在2.2cal.kaB.P.左右出现短期的湿润.巴丹吉林沙漠全新世气候变化反映了该地区在早全新世东亚夏季风降水明显增强,中全新世季风降水较强,晚全新世季风降水减弱,同时具有短时期的不稳定性.10.0cal.kaB.P.以来巴丹吉林沙漠气候总体由湿润向干旱变化,应与北半球全新世以来太阳辐射的持续减弱有关.     

川西龙泉山西坡更新世泥石流的发现及其意义

在川西地区龙泉山西坡首次发现了第四纪泥石流沉积。泥石流沉积相组合为AA1B、AA1C、AA1,反映泥石流为洪积扇扇中沉积组合,具有粘性泥石流的沉积特征。ESR测年及孢粉化石组合特征表明泥石流沉积于早-中更新世温暖湿润的气候环境下。龙泉山泥石流的形成反映了龙泉山早-中更新世之交的构造隆升,以及四川盆地盆地期夷平面的解体,是对早-中更新世之交青藏高原的隆起、季风的加强、暴雨式降水出现的沉积响应,对于研究四川盆地西部及青藏高原东缘第四纪构造运动及古气候特征具有重要的意义。     

Holocene environmental change inferred from the loess–palaeosol sequences adjacent to the floodplain of the Yellow River, China

Chinese loess deposits are generally considered to be the product of dust storms and dust falls from the central Asia arid zones that were transported across China by the northwesterly continental monsoon. In contrast, the Zhengzhou Loess found southeast of the Loess Plateau, adjacent to the floodplain of the Yellow River, records a different eolian regime and dust source. The Zhengzhou Loess was investigated by field observations, measurements of magnetic susceptibility, particle-size distribution, loss-on-ignition, CaCO₃ and chemical contents. Both field observations and the laboratory results indicate that, during the last glacial, the Zhengzhou Loess was supplied by two different eolian regimes and dust sources, one was from the fresh flood deposits of the Yellow River driven by the northeast winds from the low-lying floodplain, and the other was from the dust storms and dust falls that traveled across the Loess Plateau driven by the northwesterly continental monsoon from the central Asian arid lands. The early Holocene, 11,500–8500 a BP, was a transition during the change in eolian regime and dust source because of the weakened northwesterly monsoon along with the global climatic amelioration. Following the retreat of the northwesterly monsoon from the onset of the mid-Holocene Climatic Optimum at 8500 a BP, dust supply from the drifting sand zone on the Yellow River floodplain became dominant because of the intensified strength of the northeast winds from the Bohai Sea. From 3100 a BP onwards, climatic aridity and extensive human disturbance have resulted in intensive eolian processes causing the incursion of the drifting sand into the Zhengzhou Loess zone. These results show that loess accumulation is more complex than traditionally assumed. The origin of loess deposits elsewhere outside the Loess Plateau may be related to dust sources derived from alluvial sediments of major river systems.     

Intensification of the East Asian Monsoon in Southern China at about 300–400 kaBP Inferred from Eolian Deposits in the Middle-lower Reaches of the Yangtze River

In the East Asian monsoon region,eolian deposits widely distributed in the middle-lower reaches of the Yantgze River are among the best materials available for studies on Quaternary climate change in the subtropical zone of Southern China.Typical eolian deposits in this region include upper Xiashu Loess(XL) and underlying Vermiculated Red Soil(VRS) layers.In this paper,chronological and paleoclimatic studies are conducted on an eolian deposit sequence near Jiujiang(JJ) city in northern Jiangxi province.A magnetostratigraphic study,combined with optically stimulated luminescence(OSL) dating,is conducted on the JJ section and provides further evidence that eolian deposits in the middle-lower reaches of the Yangtze River have been formed since the late Early Pleistocene,and that the boundary age between the XL and VRS layers is about 300-400 kaBP.In grain-size records of the JJ section,the median grain-size and content of the 30 μm size fraction increase sharply after 300-400 kaBP,representing an East Asian winter monsoon intensification event.Further pollen analysis reveals differing pollen assemblages before and after 300-400 kaBP:there is an evident increase in plants adapted to grow in a warm humid environment after 300-400 kaBP,implying an increase in precipitation caused by intensification of the East Asian summer monsoon.Global ice volume and uplift of the Tibet Plateau(TP) are regarded as crucial factors influencing variations of the East Asian monsoon on a long-term scale.The deep-sea δ~(18)O record,which reflects variations in global ice volume,shows no obvious change after 300-400 kaBP.Moreover,the influence of global ice volume changes on the East Asian summer and winter monsoons is inverse;the global ice volume increase(decrease) implies a strengthened(weakened) winter monsoon and weakened(strengthened) summer monsoon.We therefore interpret the coupled intensifications of the East Asian summer and winter monsoons at about 300-400 kaBP to the uplift of the TP in the Middle Pleistocene.This climate event is also documented in eolian deposits from the southern margin of the Chinese Loess Plateau(CLP) and from the desert-loess transitional belt.However,it is not recorded in the loess-paleosol sequences from the central part of the CLP,thereby indicating differing climate responses to TP uplift in different regions,which requires further study.     

临夏盆地晚新生代哺乳动物群演替与青藏高原隆升背景

临夏盆地的晚新生代沉积中富含哺乳动物化石,以晚渐新世巨犀动物群、中中新世铲齿象动物群、晚中新世三趾马动物群和早更新世真马动物群的化石最为丰富。晚新生代是青藏高原快速隆升的时期,临夏盆地的4个主要哺乳动物群在构造剧烈变化的背景下发生了显著的更替。通过对不同动物群所代表的生态特征的分析,恢复了临夏盆地晚新生代以来的气候环境演变过程:晚渐新世以温暖湿润的森林环境为主,间杂有一些开阔地带;中中新世的森林更加茂密,水体更加丰富;晚中新世演变为炎热半干旱的稀树草原环境,季节性变化加强;早更新世气候寒冷而干燥,并伴有显著的海拔升高。青藏高原在晚渐新世的隆升幅度还不足以阻挡大型哺乳动物在高原南北的交流,但到中中新世已成为明显的障碍,至晚中新世对动物迁徙的阻碍作用更加突出,而临夏盆地在早更新世已经达到相当大的高度,产生了一个高原或高山的动物群     

Early Cretaceous Paleoclimate Characteristics of China: Clues from Continental Climate-indicative Sediments

The Cretaceous was one of the most remarkable ‘greenhouse' climate periods in geological history. Most of the reported studies of the Cretaceous paleoclimate are based upon marine sedimentary records. Large spatial scale paleoclimatic reconstruction, which has a higher time resolution based upon continental sediments in China, is rarely found. This study presents paleoclimate reconstruction for the six time periods of the Early Cretaceous in China by employing continental climate-indicative sediments, including calcareous deposits, coal, oil shale, gypsum, halite, desert sedimentary systems, ferruginous deposits and laterite, copper-bearing deposits, limestone and dolomite. Based on the distribution of the association of climate-indicative sediments and the influences of paleotopography and orogenic belts(or important structural belts) on climate, seven climatic zones have been identified: 1) a warm and humid zone; 2) a warm and humid-warm and arid zone; 3) a warm and arid zone; 4) an arid and hot zone; 5) the Tibet hot and humid zone; 6) a hot and arid-semiarid zone; and 7) a hot and humid-hot and arid one. It is found that the Early Cretaceous climatic zones of China were nearly latitudinally distributed from northwest to southeast. The aridhot climatic zone expanded in the Aptian, suggesting that a hotter and drier climate prevailed in later period of the Early Cretaceous. Conversely, the humid climatic zone expanded in the Albian, indicating that a wetter climate appeared at the end of the Early Cretaceous. The overall distribution pattern of the seven climatic zones indicates that a hot-warm and arid climate was predominant in China; this coincides with a global ‘greenhouse climate' background. However, palaeogeographic features and specific geologic events, such as the existence and disappearance of the eastern high plateau, and the uplift and denudation of Yinshan, Yanshan, Tianshan, Qinling and Dabie Mountains, led to distinctive regional climatic features of the Cretaceous in China.     

The Pattern of General Atmospheric Circulation in Eastern Asia Before the Uplift of the Tibetan Plateau

THE PATTERN OF GENERAL ATMOSPHERIC CIRCULATION IN EASTERN ASIA BEFORE THE UPLIFT OF THE TIBETAN PLATEAU     

三大自然区过渡地带近50年来气候类型变化及其对气候变化的响应

The transition area of three natural zones (Eastern Monsoon Region, Arid Region of Northwest China, Qinghai Tibet Plateau Region) is influenced by the Asian monsoon and middle latitude westerly circulation because of its special geographical position. And it is more sensitive to global climate change. The Koppen climate classification, which is widely used in the world, and the accumulated temperature-dryness classification, which is usually used in China, were used to study the climate zones and changes in the region of longitude 97.5°~108°E, latitude 33°~41.5°N, from 1961 to 2010. The changing areas of each climate zone were compared to the East Asian Summer Monsoon index, the South Asian Summer Monsoon index, the Summer Westerly index, the East Asian Winter Monsoon index, the Plateau Summer Monsoon index, the North Atlantic Oscillation index, the Southern Oscillation index, NINO3.4 index, to explore the response of the transition area of three natural zones to each climate system. According to the results, this region will become wetter when the Summer Westerly or the East Asian Winter Monsoon is relatively strong. When the East Asian Summer Monsoon or the South Asian Summer Monsoon becomes strong, the climate in low altitude region of the study area will easily become drier, and the climate in high altitude region of the study area is easily to become wetter. When the Plateau Summer Monsoon is relatively strong, the climate in the study area will easily become drier. When the North Atlantic Oscillation is relatively strong, the study area will easily become wetter. And when the El Niño is relatively strong, or the Southern Oscillation is relatively weak, the study area will easily become drier. In general, the moisture status of this region is mainly controlled by the middle latitude westerly circulation. The enhancement of the Asian summer monsoon could increase the precipitation in the southeast part of this regional, but, according to the degrees of dryness and the types of climate change in this paper, warming effects could offset precipitation increasing and make the area drier. The transition area of three natural zones is influenced by multiple interactions of climate systems from East Asia. A single climatic index, such as air temperature or precipitation, can not completely represent the regional features of climate change. As a result, areas of climate zones can be used as an important index in the regional climate change assessment.     

中国东部的第四纪风尘堆积与季风变迁

历史时期的雨土及近代尘暴的研究证实,风尘堆积与冬半年强冷气流活动有关。中国东部第四纪风尘堆积(黄土和下蜀土)分布的时、空变化及其粒度的不断增粗表明,第四纪以来冬季风强度是不断增加的。季风强度的变化主要与青藏高原越来越快的整体隆升有关。青藏高原上升产生了高原季风,并对西风气流和蒙古冷高压发生影响,即从三方面对季风起到增强作用。另一方面是中新生代以来地球气候变冷,使中、高纬地带的海陆分布和地形对大气环流有更大的影响。