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1.
Given the conflicts over the proposed formation mechanisms of Xiashu loess, the question of the provenance of sediments comprising the Xiashu loess in the Yangtze River Delta has not been satisfactorily resolved. In this study, the provenance of aeolian sediments of the Yangtze River Delta, China was examined by applying the detrial zircon U–Pb dating technique, Sr–Nd isotopic and trace element compositional analysis. U-Pb dating analysis was conducted on the Xiashu loess at three locations over the Yangtze River Delta, including Huangnishan(HNS) hill, Shengshan(SS) island and the Xuancheng(XC) area. The Xiashu loess and the sediments of the Yangtze River Valley share considerable similarity in their zircon U-Pb age spectra with the same main age peak and comparable age distribution. By contrast, significant differences in the age spectra, existbetween the Xiashu loess and loess deposits of Chinese Loess Plateau(CLP). Coarse grains of the Yangtze River Delta loess may have a proximal material source identical to the sediments from the Yangtze River valley. Sr–Nd isotopic values of the Xiashu loess match those from the northern margin of the Tibetan Plateau. Rare earth element ratios independent of grain size illustrate that the values from loess of the Yangtze River Delta mostly overlap with those of CLP loess. This feature implies that loess from the Yangtze River Delta has a dominant source of distant material similar as the CLP loess. As such, we conclude that multi-proxy analysis of sediments can shed new light on tracing the provenance of aeolian loess in the Yangtze River Delta. 相似文献
2.
Sedimentary environment of vermicular red clay in South China 总被引：1，自引：0，他引：1
Increasing interest in recent years has focused on vermicular red clay(VRC) in southern China due to its controversial sedimentary environment and provenance. Grain size is a useful way to determine sedimentary environment and provenance. Fisher Linear Discriminant Analysis(LDA) is a common and widely used method for multivariate statistical analysis. Based on a proper training sample set, the LDA can be used to discuss the sediment provenance. In this study, grain size data for 77 Malan loess samples and 41 floodplain deposit samples were used as a training sample set to deduce a Fisher linear discriminant function. Then, 299 VRC samples from 6 Quaternary red clay profiles were analyzed using the discriminant function. Grain size parameters and microscopic images of quartz grains separated from the VRC were evaluated in detail to determine the VRC sedimentary environment in south China. The results show that VRC profiles can be classified into two regions: the Chiang-nan Hilly Region and Wuyi Mountains Region. The VRC samples in the Chiang-nan Hilly Region originated from eolian dust deposits. This VRC is characterized by a higher content of fine particles(20 μm) and lower average transport kinetic energy than loess in a C-M plot. The quartz grain sizes and microscope images of this VRC suggest that it could be a polyphyletic mixture of far-sourced and nearsourced eolian deposits. The far-sourced eolian deposits share similar provenance with Xiashu loess and were transported by the East Asian winter monsoon. The near-sourced eolian deposits were dust emitted from the adjacent floodplain. In the Wuyi Mountains Region, the rugged topography weakened the dustfall and strengthened the reconstructive effect of hydrodynamic forces during the Quaternary glacial periods. The VRC in this region was reworked strongly by water and retained typical hydraulic characteristics no matter the source. 相似文献
3.
Xiaohao Wen Baosheng Li Fengnian Wang Yanming Zheng Dongfeng Niu Yuejin Si Xianjiao Ou 《中国地理科学(英文版)》2012,22(1):48-62
The TMS5e sequence from the Tumen section,at the southern edge of Tengger Desert in the northwestern China,is synchronous with Marine Isotope Stage 5e(MIS5e).It consists of 16 layers of aeolian dune sands,11 layers of lacustrine loess-like facies,and 5 layers of lacustrine facies.The results of grain-size analysis shows that the palaeo-mobile dune sands,palaeo-fixed to semi-fixed dune sands and loess-like sandy loams are mainly composed of sands,ranging from 70% to 96%;their silt contents ranged from 4% to 20%,and their clay contents ranged from 1% to 5%;the climate under which the aeolian dune sands were deposited is similar to that under which modern mobile dune sands form,which is caused by the dominance of the cold,dry East Asian winter monsoon.In contrast,the lacustrine loess-like facies and lacustrine facies had a lower sand contents than those of the three aeolian dune sands,but have higher silt and clay contents,most of their sand content ranged from 30% to 60%,their silt contents ranged from 35% to 55%,and their clay contents ranged from 6% to 20%.The lacustrine loess-like facies and lacustrine facies formed under the influence of the warm,humid East Asian summer monsoon based on their similarity with modern sediments.The grain-size indicator Mz(mean grain diameter) and the SC/D value in the TMS5e sequence indicate climatic insta-bility at the southern edge of the Tengger Desert during MIS5e,with at least 14 fluctuations between a warm,humid climate and a cold,dry climate,divided into five stages:TMS5e5(139 kyr to 129.3 kyr B.P.),TMS5e4(129.3 kyr to 124 kyr B.P.),TMS5e3(124 kyr to 119.5 kyr B.P.),TMS5e2(119.5 kyr to 116.5 kyr B.P.),and TMS5e1(116.5 kyr to 113.7 kyr B.P.).These correspond roughly to MIS5e5,MIS5e4,MIS5e3,MIS5e2,and MIS5e1,respectively,in the GRIP ice core data. 相似文献
4.
XUE Jibin ZHONG Wei ZHAO Yinjuan PENG Xiaoying 《中国地理科学(英文版)》2008,18(1):54-61
Study results in this paper have indicated that the Holocene climate in Xinjiang, Northwestem China has been alternating between wet and dry conditions, and was punctuated with a series of abrupt climate shifts. A sediment core taken from Barkol Lake in the northern Xinjiang of Northwest China was analyzed at 1 cm interval for grain-size distribution. Abrupt climate shifts revealed by the grain-size proxy occurred at ca 1.4, 3.0, 4.3, 5.6, 8.0 cal kyr B.E, which were well correlated to both the abrupt shifts recorded in the North Atlantic Ocean （NAO） and the Holocene sea surface temperature （SST） cooling events in the Arabian Ocean. The correlation indicated that the climatic changes in the extreme arid Northwest China were associated with the NAO, probably via the North Atlantic Oscillation-affected westerly winds. The strength and position of westerly winds probably modulated the Siberian-Mongolian high- pressure system （winter monsoon）, and played an important role in climate change of Northwest China. Moreover, an evident drought interval during the middle Holocene was also revealed by grain-size proxy. 相似文献
5.
Wang Jianli 《中国地理科学(英文版)》1997,8(1):85-90
Estimates of the palaeo-subaerial wind direction were studied systematically for the first time by using the anisotropy of
loess magnetic susceptibility (AMS) measurements in the northwestern China. One hundred and forty undisturbed oriented aeolian
loess samples were collected from Lanzhou, Linxia and Wudu areas for AMS measurements, which indicated the subaerial wind
directions were not the same while the loess deposited. From the Early Pleistocene to Middle Pleistocene till Late Pleistocene,
the wind direction experienced an anticlockwise rotation in the studied area. We suggested this change was related to the
uplift of the Qinghai-Xizang Plateau and the adjustment of current and landform effects. 相似文献
6.
王建力 《中国地理科学(英文版)》1998,8(1):85-90
ＴＨＥＡＮＩＳＯＴＲＯＰＹＯＦＬＯＥＳＳＭＡＧＮＥＴＩＣＳＵＳＣＥＰＴＩＢＩＬＩＴＹＩＮＴＨＥＮＯＲＴＨＥＡＳＴＥＲＮＦＲＩＮＧＥＯＦＱＩＮＧＨＡＩＸＩＺＡＮＧＰＬＡＴＥＡＵＡＳＡＮＩＮＤＩＣＡＴＯＲＯＦＰＡＬＡＥＯＷＩＮＤＤＩＲＥＣＴＩＯＮＷａｎ... 相似文献
7.
This paper presents the study on two continuous glacio-lacustrine sedimentary deposits, Laotanfang (3 597 m) and Shibantang (3 689 m) located on the southern and northern sides of Hulifang peak in Yunan, China. Environmental change indexes are constructed for each deposit, based on grain size, geochemical and pollen analysis, environmental magnetic susceptibility, and 14C dating. The study of climatic environmental change since the Holocene epoch in this region shows that the climate fluctuated at different stages during the early Holocene, that is, the climate was cool and wet during 8 4-7 7 ka, cold and wet during 7 7-6 5 ka, cold and dry during 6 5-4 7 ka, cool and wet during 4 7-2 1 ka, warm and wet during 2 1-1 0 ka, and warmer and wet since 1 ka. These findings reflect the overlapping influences of the southwest and southeast monsoons in different times during the Holocene in the north part of southwestern China are in accord with other Holocene climate change models in this part of China. 相似文献
8.
Ding-ding Du Cheng-jun Zhang Muhammad Saleem Mughal Xiao-yu Wang Dembele Blaise Jun-ping Gao Yuan Ma Xin-rong Luo 《山地科学学报》2018,15(3):532-547
The Northern Qaidam Basin is located at the northeastern part of the Qinghai-Tibetan Plateau. It contains very thick Cenozoic terrestrial clastic sediments, which records the formation of the northern Qaidam Basin due to compressional deformation during the Indo-Asian collision. In this paper, we used detrital apatite fission-track thermochronology, including 4 sandstones and 2 conglomerates samples from the Lulehe section, to reveal the Cenozoic evolution of the northern Qaidam Basin. Fission-track dating indicated the source region of the Lulehe section has experienced important cooling and uplifting in the Late Cretaceous (at ~85.1 Ma and ~65 Ma) and the Eocene (~52 Ma), respectively. The AFT age distribution on the section suggested that the provenance of Lulehe section sediments were mainly derived from the south Qilian Shan (Qilian Mountains) and Altun Shan (Altun Mountains), and two significantly provenance changes may occur at 43.4-46.1 Ma and ~37.8 Ma, respectively. The results may have strong constrains on the Cenozoic deformation and tectonic evolution of the northern Qaidam Basin and Qinghai-Tibet Plateau. 相似文献
9.
LI Zhi-wen SUN Li LI Bao-sheng WANG Feng-nian DU Ding-ding SONG You-gui ZHANG Hui-Juan CHEN Liu-qin XU Dan 《山地科学学报》2022,(2):418-432
Previous studies on the amplitude of East Asian summer monsoon (EASM) changes mainly focused on northern China (represented by the Loess Plateau).However,a rare... 相似文献
10.
为研究亚非夏季风降水的时空变化特征及其与热带东风急流的相关性,利用1948-2008年61年NCEP／NCAR再分析资料,采用经验正交函数分解和奇异值分解等方法讨论了亚非夏季风降水的变化及其与热带东风急流的关系。结果表明：从包括撒赫勒在内的北非地区到印度西北部、青藏高原南部,直到中国华北东北地区,是亚非夏季降水的最主要的空间分布型式。亚非夏季风降水总体呈现出逐年递减的趋势。多年亚非季风区夏季降水分布与热带东风急流的强度有密切关系,在急流不同部位降水特征不同。亚非夏季风降水与热带东风急流呈显著正相关,二者的分布趋势在极大程度上吻合。 相似文献
11.
为了探讨首次在闽西发现的网纹红土的成因,采用将永安地区网纹红土的粒度实验结果与典型风成沉积物、现代河流沉积物以及其他地区的网纹红土相对比的方法,对位于闽西永安地区的网纹红土剖面进行了粒度分析。结果表明:永安地区网纹红土以粉砂级组分为主,黏粒组分次之,砂级组分最少,全部样品属于黏土质粉砂;剖面从上到下粉砂级组分、黏粒组分逐渐增多,砂级组分明显逐渐减少;10~50 μm粒组体积分数均值为29.71%,远低于典型风成沉积物;沉积物岩性三角图、粒度参数特征、粒度参数散点图、Mz-A图和Mz-L图以及频率曲线显示永安地区网纹红土不是风积成因,但也不是典型的冲积成因;判别函数结果均为正值,显示了水成成因;永安地区网纹红土的成因是两方面的,为冲积成因下经过强烈化学风化作用的产物,福建其他地区、江西泰和以及广东东江一级阶地的网纹红土也具有相同成因。研究结果进一步明确了福建省境内网纹红土的分布,同时更深入理解与认识了网纹红土的成因。 相似文献
12.
Effects of site conditions on earthquake ground motion and their applications in seismic design in loess region 总被引：3，自引：0，他引：3
The Loess Plateau is an earthquake prone region of China, where the effects of loess deposit on ground motion were discovered during the 2008 Wenchuan earthquake (Ms8.0) and the 2013 Minxian-Zhangxian earthquake (Ms6.6). The field investigations, observations, and analyses indicated that large number of casualties and tremendous economic losses were caused not only by collapse and damage of houses with poor seismic performance, landslides, but also amplification effects of site conditions, topography and thickness of loess deposit, on ground motion. In this paper, we chose Dazhai Village and Majiagou Village as the typical loess site affected by the two earthquakes for intensity evaluation, borehole exploration, temporary strong motion array, micro tremor survey, and numerical analysis. The aim is to explore the relations between amplification factors and site conditions in terms of topography and thickness of loess deposit. We also developed site amplification factors of ground motion for engineering design consideration at loess sites. The results showed that the amplification effects are more predominant with increase in thickness of loess deposit and slope height. The amplification may increase seismic intensity by 1 degree, PGA and predominant period by 2 times, respectively. 相似文献
13.
14.
Wei ZHANG Chuanchuan LI Zhijiu CUI Jinliang FENG . College of Urban Environmental Sciences Liaoning Normal University Dalian Liaoning China. College of Environmental Sciences Peking University Beijing China 《东北亚地学研究》2008,11(3):156-167
This paper presents the study on two continuous glacio-lacustrine sedimentary deposits, Laotanfang （3 597 m） and Shibantang （3 689 m） located on the southern and northern sides of Hulifang peak in Yunan, China. Environmental change indexes are constructed for each deposit, based on grain size, geochemical and pollen analysis, environmental magnetic susceptibility, and 14C dating. The study of climatic environmental change since the Holocene epoch in this region shows that the climate fluctuated at different stages during the early Holocene, that is, the climate was cool and wet during 8.4-7. 7r ka, cold and wet during 7.7-6. 5 ka, cold and dry during 6. 5-4.7 ka, cool and wet during 4.7-2. 1 ka, warm and wet during 2. 1-1.0 ka, and warmer and wet since 1 ka. These findings reflect the overlapping influences of the southwest and southeast monsoons in different times during the Holocene in the north part of southwestern China are in accord with other Holocene climate change models in this part of China. 相似文献
15.
评估高温灾害的危险性变化,能够为区域高温灾害风险管理和制定减灾措施提供决策依据。本研究选取高温日数、最高温度和平均高温强度3个指标,基于1961—2020年中国2517个气象站点日最高温数据和CMIP6情景模式比较计划中SSP2-4.5情景下12个气候模式提供的2031—2099年未来气候预测数据集,用核密度概率估计方法计算了4个重现期（即5、10、20和50年）下3个指标的取值,对中国未来高温危险性变化进行了评估。结果表明：① 在SSP2.4-5情景下,中国的高温日数呈现出4个危险中心,分别是：西北干旱（半干旱）地区中部、华北和华中地区的交汇区域、西南地区中部和华南地区南部,并且高温日数从这4个中心向外逐渐减少;最高温度在空间上的分布北部大于南部,东部大于西部。平均高温强度的分布则呈现出从华北地区南部、西北干旱（半干旱）地区西部和东部地区西部向我国除青藏高原地区外的其它地区减少的趋势; ② 在SSP2.4-5情景下,随着重现期年限的增长,中国地区3个高温指标均呈增长趋势且增幅较大,并且高值范围也在不断扩大;③ 3个高温指标变化值均呈现出了明显的空间聚集性,3个指标共同显示的热点区域包括西南地区北部和南部、西北干旱（半干旱）地区中部和华北、华中地区的少部分区域,这些地区发生高温灾害的可能最大,同时根据高温日数变化和最高温度变化,东部地区西部发生高温灾害可能也较大,3个指标共同显示的冷点区域包括青藏高原地区东南部、西北干旱（半干旱）地区的西部和我国东南沿海地区,这些地区几乎不会发生高温危险。 相似文献
16.
利用NECP/NCAR月平均再分析资料,研究1951～2010年夏季青藏高原主体大气热源分布、对东亚地区的环流影响及其与同期中国降水的关系.针对高原加热局地特征明显的特点,采用旋转经验正交函数等方法探讨不同类型的热源分布以及对东亚地区大气环流的影响.结果表明,当加热中心位于高原东南侧时,青藏高原夏季风加强,南亚高压偏南偏东,西太平洋副热带高压西伸加强,而东亚中高纬地区两脊一槽的经向环流分布形势明显,有利于中国长江流域的降水而不利于华南华北的降水发展.当加热中心位于高原中北部与西南地区时,青藏高原夏季风减弱,南亚高压偏西,西太副高明显偏东偏弱,中高纬环流的纬向特征明显,有利于中国地区北方降水而不利于南方地区的降水. 相似文献
17.
根据古地磁、磁化率、粒度和重矿物分析及电镜扫描石英砂表面特征等测试手段的综合研究,西宁地区的黄土可分出从S_0至L_(17)的连续黄土——古土壤序列。它包括全新世黄土、马兰黄土、离石黄土和午城黄土,形成的时间为1.2MaB·P.。黄土粒度粗,且含有两个风成细砂分层。重矿物以不透明矿物、角闪石为主,次为绿泥石、锆石和金红石等。石英砂颗粒以次棱角状为主,其次为棱角状。石英砂表面机械结构中有众多的冰川作用痕迹和风力作用痕迹。本区黄土主要来源于青藏高原第四纪局部冰盖、冰川及其外围广大冰缘地区所产生的粉砂物质。西宁大墩岭黄土剖面详细地记录了1.2MaB·P.的环境变化信息。其中1.1MaB·P.形成的L_(15)顶部的细砂分层代表1.2Ma以来最为干冷的严酷时期。L_1和L_2是末次冰期和倒数第二次冰期的产物。倒数第二次冰期比末次冰期更为干冷,极盛时期为0.155MaB·P.。S_1S_3和S_4可能代表1.2Ma以来本区最为温暖湿润的时期。 相似文献
18.
The characteristics of circulation corresponding to two kinds of indices of summer monsoon onset over the South China Sea
(SCS) have been discussed using the reanalysis data of the National Centers for Environmental Prediction-National Center for
Atmospheric Research. It is found that there are two patterns of deep convection that occur at different locations and influence
the summer monsoon onset over the SCS. One is over the Asia continent and the western Pacific corresponding to the southwesterly
of summer monsoon prevailing over the northern and central part of the SCS, while the other is near the Philippines that affects
the westerly summer monsoon as prevailing over the central and southern southern part of the SCS. Since these two kinds of
convection affecting the summer monsoon onset do not always occur together, thus the summer monsoon onset time is different
when determined by various indices. 相似文献
19.
Long term variability in the surface winds over the marginal seas of China is examined with a dominant-mode singular value decomposition method. Both interannual and interdecadal patterns are found to be seasonally and spatially dependent, with reanalyses and satellite remote sensing data yielding highly consistent results. The study reveals that summer monsoon winds over the East China Sea experienced an interdecadal weakening in the late 1960s and began a persistent recovery in 2005. The study also shows gradual weakening of the winter monsoon in the southern South China Sea by more than 2m/s since the 1960s, with corroboration from coastal climate stations in Borneo. This phenomenon has not been reported in previous monsoon studies. 相似文献
20.
鲁南微山县郗山稀土矿为我国北方三大富轻稀土矿之一,也是山东省最重要的轻稀土矿产地,其周边地区是山东省重要的稀土矿远景找矿预测区。通过综合找矿方法在山东省枣庄市薛城地区开展矿产调查工作,发现了重要的稀土矿找矿线索,其成矿类型、成矿时期及成矿模式等与郗山稀土矿具有内在的时空、成因联系。该文以利用综合找矿方法在枣庄薛城地区稀土矿调查评价中的应用为实例,通过与郗山稀土矿的对比探讨,分析了该区稀土矿的成矿规律及成矿模式,并结合区域成矿背景进行了成矿预测,对鲁南地区今后稀土矿的调查评价工作具有指导作用。 相似文献