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在被认为孢粉贫乏的黄土中分析出了大量孢粉,首次作出了黄土地层的孢粉浓度图式。根据１０余个剖面上孢粉组合的变化,阐明了晚更新世的植被与气候在时间上演替与空间上分布的规律,证明了各地植被在时间上的演变韵律十分相似,说明它们同受全球气候变化的控制,但同一时期在空间上各地植被不尽相同,此乃局地自然环境差异所致。根据植被变化重建了古气温曲线。 相似文献
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末次间冰期-末次冰期柴达木盆地东部气候演化形式 总被引：8，自引：3，他引：5
柴达木盆地第四系富含介形类化石，介形类生物组合可以反映古气候变化。以盆地东部达参1井中的两种主要介形类(Ilyocypris inermis和Cyprideis torasa)的丰度特征为气候指标，对末次间冰期和末次冰期的盆地气候演变形式进行了恢复。认为柴达木盆地东部末次间冰期和末次冰期的气候演化既有着和全球同步的特点，也有着本区域独自的特征。介形类丰度曲线表明：末次间冰期(MIS5)，以Cyprideis torasa为主，整体上为暖型气候，依据介形类特征，又可分为5e，5c．5a三个暖期和5d．5b两个冷期，暖期到冷期都以介形类丰度的大幅突降为特征；末次冰期(MIS4-2)以Ilyocypris inermis为主，整体为冷型气候。其中，早冰阶(MIS4)两种介形类丰度都较低．而间冰阶(MIS3)介形类丰度明显增高，并可划分为3c．3a两个暖期和3b一个冷期。在间冰阶结束之后，介形类大量消失，llyocypris inermis完全灭绝，石盐大范围析出．盆地进入了末次冰期盛冰阶(MIS2)。 相似文献
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LIBao-sheng GAOShang-yu DONGGuang-rong JINHe-ling 《中国地理科学(英文版)》2005,15(1):34-41
1INTRODUCTIONOrdosDesertisageneral appellationof Qubqi Desert onthe north, Hedong Sandy Landonthesouthwest and MuUs Desert on the southeast (Fig. 1). It is situated on atransitional zone from arid desert steppe to semi-aridsteppe between ariddesertinNorth… 相似文献
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Study on the carbonate content and oxygen isotope of a sediment section in Dabusu Lake revealed that this region has experienced several cold-wet and warm-dry climatic cycles since 15400 a BP. It was about 6740 a BP when the climate in the region reached a relatively stable warm stage, so that the lake water was gradually condensed and finally a saline lake was formed. 相似文献
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研究剖面位于洛川源北部的富县县城东郊。剖面由第一层古土壤(S_1)、马兰黄土(L_1)和全新世古土壤(S_0)组成。孢粉分析结果表明,黄土地层中孢粉非常丰富,为恢复古植被与古气候提供了可靠依据。S_1的植被是以榛、菊、蒿为主的疏林草原,有亚热带树种出现,反映了末次冰期的温湿气候。L_1时主要为菊、蒿干草原,气候冷干,其间有四次乔木增多期,反映了末次间冰期中有四次间冰阶的相对温湿气候波动。近代耕土中为以松、藜、中华卷柏为主的森林草原,反映了全新世某个时期比较温凉干旱的气候。 相似文献
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Jie Chen Tai-bao Yang G.G. Matishov A.A. Velichko Biao Zeng Yi He Pei-hong Shi 《山地科学学报》2018,15(3):504-518
A reliable chronology is essentially critical for correlating loess records with other paleoenvironmental time series, as well as for continuing improvements in the reconstruction of paleoenvironment and paleoclimate changes. It is exactly that the scarcity of chronologies across the Sea of Azov has limited the interpretation of climatic and environmental information in the East European Plain. In view of this, this paper conducted an exploratory study to investigate whether the optically stimulated luminescence (OSL) dating of mediumgrained quartz could be used to obtain a set of chronologies and the age models could be used to establish an independent time scale since the Late Pleistocene for the Sea of Azov loess. The results showed that an internally consistent set of optical ages for the Azov loess deposited up to ~76 ka. In addition, the ages developed based on magnetic susceptibility and grain size ages models showed good comparability with independent OSL ages at an acceptable range, suggesting that it might be practicable to establish an independent time scale using age models at the Sea of Azov loess, at least for the uppermost part of the Chumbur-Kosa section. Comparison with the ages based on two age models, the grain size ages using fine-grain fractions may provide a more reliable chronological sequence at the Azov loess since the Late Pleistocene. With the help of absolute ages and climate proxies (magnetic susceptibility and grain size), paleoclimatic change in the Sea of Azov have been traced for the Late Pleistocene. 相似文献
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To reconstruct the productivity changes for the last 10 500 a in the northeastern East China Sea (ECS), biogenic compounds (such as carbonate, organic carbon and opal), marine micropaleontological fossils (planktonic foraminifera, benthic foraminifera, radiolarian and silicoflagellate) and the compositional characters of benthic foraminifera fauna analyses were carried out on a sediment core DOC082 obtained from the western slope of Okinawa Trough (29°13.93′N, 128°08.53′E; 1 128 m water depth). The long-term changes of biogenic and micropaleontological proxies display some similarities through the last 10 500 a, which show three different phases: lower values are recorded during the early and middle Holocene (before about 4 000 a BP), followed by an abrupt and remarkable increase at about 4 000 a BP, the late Holocene (after about 3 000 a BP) is characterized by continuously high values. The multi-proxy data of paleoproductivity and percents of benthic foraminifera genera (Uvigerina and Bulimina) show that during the early and middle Holocene (10 500–4 000 a BP) productivity was relatively low with a sudden and distinct increase at about 4 000 a BP, and the late Holocene (3 400–0 a BP) is marked by significantly higher productivity. Also, the radiolarian-based sea surface temperature (SST) records reveal a distinct decline in SST in the late Holocene after 3 200 a BP, very different from the early and middle Holocene. For the last 3 000 a, the enhanced biological productivity and distinctly lower SST indicate a major change of oceanographic conditions in the northeastern ECS. These marine environmental anomalies are consistent with other paleoclimatic records for the late Holocene in the Chinese continent and its surrounding regions. After analyzing the mechanisms of modern productivity and SST changes in the northeastern ECS, and based on the climatic anomalies in the Chinese continent and variations in the Kuroshio Current during modern El Niño periods, we suggest that the anomalous environmental conditions in the northeastern ECS may imply intensified El Niño activity during the late Holocene. 相似文献
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黄土作为典型的多物源沉积物，粒度分布常呈现多峰分布。端元分析可以从复杂的沉积物粒度中分离出代表不同沉积物源和沉积动力的端元组分，在黄土研究中得到了广泛应用。利用Paterson参数化端元模型对处于毛乌素沙漠东南缘的靖边三道沟剖面粒度进行端元分离与解释，并讨论其代表的环境意义。靖边三道沟黄土可分为4个端元:EM1（众数粒径8.93 μm）为背景粉尘；EM2（众数粒径25.18 μm）为与季风环流有关的组分；EM3（众数粒径39.91 μm）和EM4（众数粒径56.37 μm）都是与冬季风有关的组分，其中EM3为黄土高原黄土主要组分，EM4与现代沙尘暴的粒级大致相同。通过对各端元组分随年龄变化的曲线进行分析，得到以下结论:该剖面记录了靖边地区自MIS 3以来经历了MIS 3（32.8~29.8 ka BP）、LGM（29.8~22.8 ka BP）、冰消期（22.8~11.3 ka BP）和全新世（8.7~1.7 ka BP）共4个气候时期。端元组分还记录了冰消期H 1事件（16.2~13.8 ka BP）、B/A事件（13.8~12.8 ka BP）、YD事件（12.8~11.3 ka BP）共3次气候快速变化事件和D-O旋回。该剖面还记录了毛乌素沙漠末次冰期经历的3次主要的扩张-收缩旋回以及全新世8.7~8.2，6.0~5.0，3.5~2.5 ka共3次干旱沙进事件。 相似文献
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甘肃通渭县黄土堆积区全新世环境变迁 总被引：5，自引：2，他引：3
通过对甘肃通渭县四家庙全新世黄土剖面的粒度和磁化率分析。并依据前人研究成果对年均气温和年均降水量的相应恢复，揭示了该区全新世期间气候演化的特点和规律。分析认为，研究区全新世以来的环境变化是不稳定的，无论古土壤发育期还是黄土堆积期，气候都具有频繁的次级波动。尤其在全新世中期。两层古土壤间的黄土夹层，反映该区在全新世大暖期经历过一次历时千年之久的气候显著恶化事件。 相似文献
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High-precision isotope composition determinations using multicollector, magnetic-sector inductively coupled plasma mass spectrometry (MC-ICPMS) have recently revealed that some transition metal isotopes such as those of Mo, Fe, Cu, Zn etc. can be used as biogeochemical tracers in global change research.The Mo isotope system may be useful in paleoredox investigations indicating that δ^97 ^95Mo in seawater may co-vary with changes in the relative proportions of anoxic and oxic sedimentation in the ocean, and that this variation may be recorded in δ^97 ^95Mo of anoxic sediments. The Mo continental flux into the oceans and the global Mo isotope budget can be estimated from δ^97 ^95M0 values. The Fe isotope composition in seawater is an important issue because Fe plays a controlling role in biological productivity in the oceans and its abundance in seawater may have substantial effect on climate changes. Iron isotope fractionations could result from bio- and abio-processes and have about 0.1% variation ( δ^56 ^54Fe), so Fe isotopes considered alone cannot be used to distinguish the products of abiotic and biotic Fe processing in geological records. Cu and Zn isotopes are also used as biogeochemical tracers, but the researches are relatively less. This review mainly focuses on the methods for preparation, purification and determination of new isotope tracer samples, and on isotope applications in marine environmental changes. 相似文献
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天水谢家湾全新世环境变迁及人地关系演化 总被引：2，自引：1，他引：1
在野外详细观测的基础上，对天水谢家湾全新世黄土剖面以2cm为间距进行了连续采样，并对所有样品作了磁化率和粒度分析，结果综合反映出研究区自全新世以来，经历了早期升温、中期基本暖湿、晚期趋于干冷的气候环境演化阶段，其中全新世中期在总体温湿的大背景下，存在频繁的气候波动。以此为基础，结合对渭河文化的历史研究资料，探讨了区内约1万年以来的人地关系演化历史，指出人地关系的和谐与统一，对人类社会发展具有重要意义。 相似文献
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QIANGMing-rui LISent 《中国地理科学(英文版)》2004,14(2):117-121
Based on investigations of the Zhongwei Nanshan aeolian section situated in the southeastern margin of Tengger Dcsert, carbon-14 and TL (thermoluminescence) dating results and paleoclimatic proxies such as magnetic susceptibility and grain size, we inferred that the northwestern margin of East Asian monsoon region experienced abrupt climatic changes during the last deglaciation. Six oscillation events were identified: Oldest Dryas, Belling, Older Dryas, AllerФd, lntra-AllerФd Cold Period (1ACP) and Younger Dryas (YD). The summer monsoon was weaker during Oldest Dryas and Younger Dryas when the winter monsoon was stronger. However, during the B/A (BФlling/AllerФd) period, the summer monsoon strengthened, reflected by magnetic susceptibility, when the winter monsoon also became strong, which is different from the paleoclimatic pattern established in the East Asian monsoon region. Furthermore,the summer monsoon was nearly in phase with the climate changes inferred from the oxygen isotopic records of Greenland ice cores. It could be speculated that the variations of the sea ice cover in the high latitudes of the North Hemisphere affected the high pressure of Asian continent and the changes of the winter monsoon inland. On the other hand,the sea ice cover variations might have indirectly caused the occurrence of ENSO events that has tightly been related to the summer monsoon in northwest margin of East Asian monsoon region. 相似文献
14.
During the summers of 1999 and 2000, sampling was carried out in Mt.Yulong, for the investigation of the spatial distribution of oxygen stable isotope in the atmospheric-glacial-hydro system and similar results obtained in the two years have confirmed our conclusion. There is an evident negative correlation between stable isotopic composition and air temperature-precipitation amount, suggesting that there exits a strong “precipitation amount effect” in this typical monsoon temperate-glacier region. There are marked differences between the δ1'O values in winter-accumulated snow, glacial meltwater, summer precipitation and glacier-feeding stream. Under the control of varied climatic conditions, spatial and temporal variations of above glacialhydro mediums are apparent. Isotopic depletion or fractionation and ionic changes had occurred during the phase-change and transformation processes of snow-ice, icemeltwater, flowing of runoff and contact with bedrock. The variation of stable isotope in a runoff can reflect not only its own flowing process but also its different feeding sources. 相似文献
15.
Probe into the origin, development and evolution model of shelf desertizational environment in the last stage of Late Pleistocene 总被引：1，自引：0，他引：1
MPmMARYDEVELOPMENTOFMDESERTIZATIONCONCEPTAubrevil(l949)definedthenewterm"desertification"asthetransforrnationfromtropicalandsubtropicalforestintospaxsegrasslands.Manydesertenvirorirnentresearchersbelievethatdesertandthedesertfficationenvironmentarenotonlytheresultofmodernen-vironmentdeterioraion,butwerealsopresentingeo1ogicalPeriodsheforetheoriginofInankind.Thewords`'desertification'and'desertiZaion'linEnglishlangUageliteraure,arecOllectivelycalled"ShaMoHua"inChinese-Thef… 相似文献
16.
黄土沟谷是黄土地貌中最有活力、最具变化、最富特色的对象单元,黄土高原千沟万壑的地貌形态以及触目惊心的侵蚀状态也让区域内沟谷地貌的形成、发育及演化问题成为研究中焦点及前沿性科学问题。近年来,诸多学者采用地学测年法、特征表达法、监测模拟法力图实现对黄土沟谷发育演化进程中“过去-现代-未来”的科学认知。这些研究在相当程度上丰富了黄土沟谷发育过程的认知。本文梳理了黄土高原沟谷地貌演化相关研究的现状,并从黄土高原地貌演化、黄土沟谷发育、基于DEM的沟谷信息提取与表达等研究进行了系统的回顾、梳理与分析。此外,本文提出“黄土沟道剖面群组”概念与方法,试图从新的视角审视黄土沟谷地貌发育演化过程。沟道剖面在黄土沟谷发育演化进程中传递物质能量和累积地形动力,并通过径流节点的串联实现剖面群的连接与组合,形成独特的剖面“群组”模式;该沟道剖面群组是集黄土沟谷地貌特征与过程于一体的综合信息集成体,其三维空间结构是对黄土沟谷地貌发育演化的高度抽象与映射,并可望进一步丰富黄土高原数字地形分析理论与方法体系,为黄土高原黄土地貌成因机理与空间分异格局带来创新的认识。 相似文献
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持续引水灌溉改变了马兰黄土的结构, 降低了土体的抗剪强度, 导致黑方台地区黄土滑坡频繁发生, 严重影响着当地居民生命和财产安全。为了明析马兰黄土的渗透过程, 取黑方台马兰黄土为研究对象, 分别开展核磁共振(NMR)试验及扫描电镜(SEM)试验, 以解释此类黄土在不同初始含水率及不同干密度下的渗透特性及结构损伤微观特征。研究结果表明: 入渗速率与土体初始含水率呈负相关关系, 土体初始含水率越高, 其充水微小孔隙增加速率越慢, 充水中大孔隙增加速率越快; 入渗速率与土体干密度呈负相关关系, 且会率先形成高含水率区域, 土体干密度越大, 其充水微小孔隙增加越慢, 充水中大孔隙增加越快。入渗前后对比发现, 试样初始含水率越高, 微小孔隙增加比例越小, 颗粒间接触方式变化越不明显; 干密度越大的试样不同孔隙体积基本按等量变化, 接触面积明显减少, 形成更多的架空孔隙, 连通性较好, 具有较好的储水能力。入渗后试样原本的致密结构丧失, 颗粒破碎严重, 部分细长状颗粒向似椭圆状颗粒演化, 颗粒间接触方式变为点边接触, 粒间胶结作用遭受损伤破坏, 甚至部分团粒中颗粒分离、脱落, 使得土体强度丧失, 最终导致滑坡发生。研究结果可为黄土滑坡的防治提供依据。 相似文献
18.
碳同位素地层学是寒武系地层划分与对比的重要手段。通过对豫北驴驮沟剖面碳酸盐岩地层进行碳同位素分析发现,驴驮沟剖面寒武系鼓山阶(Drumian)底界附近的碳酸盐岩的δ 13C值分布于3.1‰~-1.7‰之间,δ 18O值分布于-3.9‰~-9.4‰之间。δ 13C、δ 18O之前的非协变关系指示碳同位素组成比较稳定。鼓山阶底界附近δ 13C表现为负漂移演化趋势,漂移幅度为3.0‰,最低值为-1.7‰,出现在三叶虫Proasaphiscus 首现位置15 m之下。出现负漂移的位置和负漂移的幅度与华南湘西王村剖面、美国犹他州Drum Mountains等剖面的鼓山阶底部的负漂Drum carbon isotope excursion(DICE)一致,表明DICE负漂移具有洲际对比意义,可作为寒武系鼓山阶划分和对比的工具。负漂移峰值处岩性为位于青灰色页岩之间的薄层灰岩夹层,超覆于鲕粒灰岩之上,因此,寒武系鼓山阶底部附近的DICE负漂移对应于苗岭世早期的海侵时期。 相似文献
19.
Influences of soil moisture and salt content on loess shear strength in the Xining Basin,northeastern Qinghai-Tibet Plateau 总被引：1，自引：0，他引：1
FU Jiang-tao HU Xia-song LI Xi-lai YU Dong-mei LIU Ya-bin YANG You-Qing QI Zhao-xin LI Shu-xia 《山地科学学报》2019,(5)
Moisture and salt content of soil are the two predominant factors influencing its shear strength. This study aims to investigate the effects of these two factors on shear strength behavior of loess in the Xining Basin of Northeast Qinghai-Tibet Plateau, where such geological hazards as soil erosion, landslides collapse and debris flows are widespread due to the highly erodible loess. Salinized loess soil collected from the test site was desalinized through salt-leaching in the laboratory. The desalinized and oven-dried loess samples were also artificially moisturized and salinized in order to examine how soil salinity affects its shear strength at different moisture levels. Soil samples prepared in different ways(moisturizing, salt-leaching, and salinized) were measured to determine soil cohesion and internal friction angle. The results show that salt-leaching up to 18 rounds almost completely removed the salt content and considerably changed the physical components of loess, but the soil type remained unchanged. As salt content increases from 0.00% to 12.00%, both the cohesion and internal friction angle exhibit an initial decrease and then increase with salt content. As moisture content is 12.00%, the salt content threshold value for both cohesion and internal friction angle is identified as 3.00%. As the moisture content rises to 16.0% and 20.00%, the salt content threshold value for cohesion is still 6.00%, but 3.00% for internal friction angle. At these thresholds soil shear strength is the lowest, below which it is inversely related to soil salinity. Beyond the thresholds, however, the relationship is positive. Dissimilar to salinity, soil moisture content exerts an adverse effect on shear strength of loess. The findings of this study can provide a valuable guidance on stabilizing the engineering properties of salinized loess to prevent slope failures during heavy rainfall events. 相似文献