微量元素记录的毛乌素沙漠全新世气候波动--以萨拉乌苏流域DGS1层段为例

选取毛乌素沙漠东南缘萨拉乌苏河流域具有代表性的滴哨沟湾剖面全新统(DGS1层段),结合微量元素与测年分析结果,探讨了该地全新世千年尺度的气候波动.结果表明,P、V、Cu、Zn、Sr、Ni、As、Cr、Pb属于易迁移-较稳定元素,其含量在沉积相中主要呈现为古土壤< 沙丘砂 <湖沼相,Co、Rb、Nb、Ba、Cl、Zr属于稳定-惰性元素,主要呈现为古土壤 >沙丘砂 >湖沼相,说明沙丘砂是冬季风主导下的沉积,古土壤和湖沼相是夏季风主导下的沉积.以Rb和Sr两种元素在垂向上峰谷交替的变化特征为依据,将DGS1记录的全新世气候分为升温期(11 000~10 130 a B.P.)、大暖期(10 130~6 590 a B.P.)、降温期(6 590~3 760 a B.P.)和寒冷期(3 760~0 a B.P.)四个阶段,这与国内外的相关研究结果一致,表明萨拉乌苏河流域全新世的气候变化是全球环境变化影响下的结果.     

150ka B.P.以来萨拉乌苏河流域主元素变动旋回

萨拉乌苏河流域米浪沟湾剖面150kaB.P.以来存在27个由风成砂与河湖相和古土壤构成的沉积旋回。通常后两者的Al2O3、TFe、Mn、TiO2、K2O、MgO、CaO和Na2O含量明显高于前者,而SiO2则相反,构成了与沉积旋回相应的150kaB.P.以来27个元素变化旋回。结合各元素的化学迁移特性、研究区所在的鄂尔多斯高原东南部洼地地貌特征以及季风沙区位置,论证了风成砂中SiO2含量增高,Al2O3、TFe、Mn、TiO2、K2O、MgO、CaO和Na2O相对降低,与干寒多风气候及其影响下石英的大量迁入有关,而河湖相和古土壤中SiO2相对迁移、Al2O3等呈聚集的势态,与暖湿气候作用下稳定性元素Al2O3、TFe、Mn、TiO2和非稳定性元素K2O、MgO、CaO、Na2O都能够从四周地表汇集于本区这种特殊的比较封闭的低地有关。研究表明,萨拉乌苏河流域150kaB.P.以来27个元素变化旋回与该时期北半球冰期-间冰期气候波动诱发的亚洲冬夏季风在毛乌素沙漠的多次更迭具有成因上的联系。     

萨拉乌苏河流域MGS1层段微量元素记录的全新世千年尺度的气候变化

本文以毛乌素沙漠东南缘萨拉乌苏河流域米浪沟湾剖面MGS1层段为代表,试图通过对其的微量元素分析结果探讨该地全新世千年尺度的气候变化.在分析的14种微量元素中,除Cr和Zn以外的12种元素P、Pb、Rb、Nb、Zr、V、Sr、Cu、Ni、As、Ba、Co含量在MGS1剖面的垂直方向上具有这样的分布规律:元素含量值在沙丘砂...     

距今30ka前后我国西北沙漠地区古环境

本文根据实地野外观测和前人的研究,对我国西北干旱地区约30kaB.P.时的环境特征进行了综合分析.选用的古环境指标主要来源于风成沉积、湖泊沉积及河流沉积,年代主要依靠14C测年.依据巴丹吉林沙漠沙丘上的钙质胶结层、植物残体、塔克拉玛干沙漠河流沉积以及巴丹吉林沙漠腹地及其西北缘的高湖面,认为在30kaB.P.前后,我国西北干旱地区雨量较高,气候较湿润.柴达木盆地、腾格里沙漠西部、古尔班通古特沙漠西部及内蒙古地区湖泊同期的高湖面也支持这一观点.     

中国北方风沙沉积物气候代用指标对比研究

在浑善达克沙地和巴丹吉林沙漠各选择近NS走向的大断面采集表层样品,用筛析法对样品进行粒度分析,用Eijkelkamp碳酸钙测定仪测定其碳酸钙含量。两地沙质沉积物的粒度参数对比结果显示,巴丹吉林沙漠沙总体上比浑善达克沙地沙粗,分选性比浑善达克沙地沙好,同时在粒度分布频率曲线上表现出明显的双峰,这应与其地处冬夏季风交替地带、冬季风和夏季风搬运营力上的差别有关。巴丹吉林沙漠和浑善达克沙地沙质沉积物粒度参数上的差别反映了两地不同的风动力条件和下垫面性质。浑善达克沙地的沙粒较细在一定程度上也与该地区较湿润条件下的成土作用有关。气候差异应是导致两地沙质沉积物粒度参数区别的主导因素。碳酸钙测量结果说明,浑善达克沙地的碳酸钙含量明显低于巴丹吉林沙漠。巴丹吉林沙漠沙的碳酸钙含量从北往南呈增加趋势,与该地区年降水量的南北方向变化相一致。从对这两个地区沙质沉积物的碳酸钙含量对比中可以看出,即使在干旱背景下,当多年平均降雨量达到一定临界值时,地表碳酸钙含量将达到一最大值,随后则呈降低趋势     

巴丹吉林沙漠石英δ18O值及其物源意义

巴丹吉林沙漠是世界上沙丘最高大的沙漠,其沙源研究对认识沙漠形成、高大沙山发育和防沙治沙工程有重要意义。石英是沙漠沉积物中常见的矿物,其氧同位素值可示踪物源。采集沙漠西北部、东部、东南部高大沙山、丘间低地与湖泊以及雅布赖山前的表层沉积物,测定了样品不同粒级的石英δ18O值。结果表明:①石英δ18O值随粒级减小有增大趋势,同一样品不同粒级石英δ18O值存在较大差异,相同粒级石英δ18O值也有变化。②石英δ18O值介于9.4‰~19.3‰,均值为13.3‰（n=55）;其中沙丘沙的石英δ18O值介于9.5‰~16.6‰,均值为12.9 ‰（n=39）;湖相沉积物的石英δ18O值介于9.4‰~19.3‰,均值为14.2‰（n=16）。③区域内,<16 μm粒级的石英δ18O值与16~64 μm、125~154 μm、200~250 μm、> 300 μm粒级的石英δ18O值都存在显著差异,但200~250 μm与 > 300 μm粒级的石英δ18O值没有显著差异;经区域对比,巴丹吉林沙漠 < 16 μm粒级的石英δ18O值与柴达木盆地沙漠、蒙古戈壁风成沉积物 < 16 μm石英δ18O值无显著差异,但巴丹吉林沙漠16~64 μm粒级的石英δ18O值与蒙古戈壁风成沉积物16~64 μm石英δ18O值存在显著差异;这似乎暗示研究区的细颗粒物质可能是远源的。巴丹吉林沙漠沉积物的石英δ18O值位于火成岩石英、砂岩和变质岩石英δ18O值分布阈值内,受区域地质条件、物源混合、粒级效应等因素的影响,砂粒级的石英δ18O值所指示的母岩成份特征与祁连山区岩石的岩性有较好吻合。     

内蒙古巴丹吉林沙漠400年来大气沉降 Hg的湖泊沉积记录

Hg污染具有全球性,人类活动较少地区的湖泊沉积物对长距离输入的大气沉降Hg变化敏感。巴丹吉林沙漠中发育了约142个沙漠丘间湖泊,是研究大气沉降Hg记 录的理想材料。选择巴丹吉林沙漠东南部的宝日陶勒盖湖泊进行湖泊钻探,结合²¹⁰Pb_uns和¹³⁷Cs核素测年及THg沉积通量计算,重建了400年来巴丹吉林沙漠湖泊的THg沉积记录,并探讨了影响沙漠湖泊THg沉积的影响因素,评估了自然背景和人类活动的影响。结果表明：(1)沉积物中THg含量分布范围为1.5~17.5 ng/g,富集系数和沉积通量的分布范围分别为0.3~4.5和2.9~38.9 μg/(cm²·a)。 THg含量、富集系数和沉积通量均表现为在岩心上部近几十年富集。(2)近400年来,湖泊沉积物中背景THg(THg_岩石风化)通量变化相对稳定,主要受控于附近物源供给和区域风沙活动。大气沉降THg(THg _大气)通量自20世纪30年代以来呈逐渐增加的趋势,很大程度上反映了近几十年来人为源大气沉降THg的增加。但20世纪30年代以来岩心局部的大气沉降THg通量的峰值可能还受全球变暖和湖泊生产力增加 的影响,而20世纪30年代之前出现的峰值可能与“小冰期”冷期强烈的区域风沙活动有关。巴丹吉林沙漠湖泊400年来的THg_大气沉积通量变化与全球Hg产量和冰心中的大气Hg含量变化记录一致,是沙漠 地区大气沉降THg的可信纪录。     

The climate change during early Holocene recorded by trace elements of Shenmu section,Mu Us Desert

Through nine trace elements of the Shenmu section, Mu Us Desert is analyzed for the climate changes during Early Holocene. Except Sr, a migration process of P, Mn, Cr, Rb, Nb, Cu, Zn, and V is found in the dune sands, indicating the accumulation processes of the Asian winter monsoon-driven wind erosion and transport and deposition under the cold climatic phase. And accumulation of these elements in different layers of paleo sol dune sands is related to regional geomorphology and element properties. 8.5 winter-summer monsoon cycles in the early Holocene are observed. The duration time and climate of the stronger winter monsoon phases can be compared with the cold climate in the North Atlantic and other parts of China. The result of Red fit 3.8 power spectra shows 310a, 210a, 90a, and 70a centennial cycles for the element, which are consistent with the solar oscillation cycles. These suggest that the external solar activities of the Earth may have great influences on driving the winter and summer monsoon cycles during early Holocene.     

内蒙巴丹吉林沙漠成因的粒度分析和热发光测年新证据

巴丹吉林沙漠位于中国内蒙古自治区的西部,是中国第三大沙漠。过去通常认为该沙漠中沙丘的可能沙源来自附近的各种沉积物和岩石,包括弱水河扇的沉积物,弱固结的二叠纪页岩、白垩纪砂岩和砾岩以及戈壁阿尔泰的古老岩石。根据对风成砂的粒度观测,有证据表明在沙漠内部的风成砂沉积朝东南方向具有较弱的但又确实的变细趋势。这与沙丘横脊线的SW-NE向排列以及坡面的南东指向是一致的。因此,可以认为西北部的弱水河冲积扇是巴丹吉林沙漠风成砂的最可能的沙源。在西北部风成床沙覆盖了较老弱水河扇起源的冲积物。这种沉积物的热发光测年范围在190～100 ka BP之间。由于测量中对沉积物漂白可能不完全以及对其中平均古水含量估算均存在不确定性,同时由于对沙漠该地区风成作用开始之前堆积的沉积物进行了测年,这一数据范围代表了最大的年龄。另外三个风成砂测年结果分别接近133.66和22 ka,代表有关巴丹吉林沙漠西北部风成作用开始的最小年龄。沙漠的沙丘高度平均为200～300m,但在东南部偶尔可达450m。一些学者曾提出风成床沙覆盖了一个陡峭岛山突起的假说,来解释这些异常的空间。本次研究发现,在研究区之下是一个产状水平的白垩纪扇砾岩和砂岩的台地,可以断定在沙漠东南部呈现台地地貌,但进一步向北该台地明显延伸到这些沙丘之下。因此现在可以认为巴丹吉林沙漠中高的沙丘是不同区域气候和地貌因素相互作用的结果,而不是覆盖一个陡峭的岛山突起。对弱水河冲积扇作为巴丹吉林沙漠的主要源区的证实强调区域环境的重要性。在全新世,沿河流的绿洲植被在某种程度上阻碍了冲积扇提供沙源。现在,河西走廊的农业用水量极大地危及沿河森林,因此沿着作为天然拦沙阱的弱水河,维持足够的河水流量来保护区域性密集的沙丘植被,一定会避免具有重大威胁的沙的活动性增加。     

Holocene climate variation determined from rubidium and strontium contents and ratios of sediments collected from the BadainJaran Desert,Inner Mongolia,China

Rubidium (Rb) and strontium (Sr) contents and ratios were analyzed in 197 sediment samples collected from the CGS1 segment of the Chagelebulu Section in the Badain Jaran Desert of China to study millennial scale climate change during the Holocene. The results showed that the Rb and Sr contents and Rb/Sr ratios were low in the samples of dune sands and loess (Mz < 5.64Φ), and those values were high in the samples of loess (Mz > 5.64Φ) and paleosols, these data displayed 11 changing cycles in alternation of peaks and valleys in the chart. In addition, the Rb contents were positively correlated with Mz (mean particle diameter) and clay contents. While the correlations were weaker, Sr contents also showed a tendency to increase with increases in the Mz and clay contents. Based on a comprehensive analysis of the distribution of Rb and Sr within the CGS1 segment, it appears that the observed Rb and Sr contents and ratios varied in accordance with fluctuations of the East Asian winter and summer monsoons. In terms of timing and climate, low values (C1–C11) resulting from winter monsoons had a strong correlation with cold events in the North Atlantic: the period C1 corresponded to times ranging from 400 a to 1400 a and the periods C2, C3, C4, C7, C9, C10, and C11 corresponded to times of 3000 a, 4000 a, 5900 a, 8200 a, 9400 a, 10,300 a, and 11,000 a, respectively. The cold event C5 (6200 a) was also discovered in the North Atlantic in recent; and C6 (7100 a), C8 (8700 a) were discovered in some other places of China. These cold events indicated by Rb and Sr contents and ratios in the Chagelebulu Section of the Badain Jaran Desert recorded the regional response of global climate change during the Holocene.     

Recharge to the inter-dune lakes and Holocene climatic changes in the Badain Jaran Desert, western China

We present new estimates on evaporation and groundwater recharge in the Badain Jaran Desert, western Inner Mongolia of northwestern China, based on a modified Penman Equation suitable for lakes in China. Geochemical data and water balance calculations suggest that local rainfall makes a significant contribution to groundwater recharge and that past lake-level variations in this desert environment should reflect palaeoclimatic changes. The chronology of lake-level change, established by radiocarbon and U-series disequilibrium dating methods, indicates high lake levels and a wetter climate beginning at ca. 10 ka and lasting until the late mid-Holocene in the Badain Jaran Desert. The greatest extension of lakes in the inter-dune depressions indicates that the water availability was greatest during the mid-Holocene. Relicts of Neolithic tools and pottery of Qijia Culture (2400-1900 BC) suggest relatively intensive human activity in the Badain Jaran Desert during the early and middle Holocene, supporting our interpretation of a less harsh environment. Wetter climates during the Holocene were likely triggered by an intensified East Asian summer monsoon associated with strong insolation.     

陕西洛川黄土的粒度分维值及其意义

对陕西洛川剖面１５８０个黄土样品的粒度数据分析表明,黄土的基本粒级,即在２－５０μｍ的标度范围内,粒度分布具有分形特征。黄土的粒度分维值在２．１６－２．５１之间,平均值为２．３２;而古土壤的粒度分维值在２．２３－２．５１之间,平均值为２．４１;粒芳分维值对黄土与古土壤的形成环境的演变,有良好的指示意义。粒度分雏值显示,250万年以来,东亚季风不断增强,变化周期和变化幅度逐渐变大。在早更新世,季风较弱,变化周期短．变化幅度小,表现为2～4万年的周期;而在晚更新世,季风较强,冬季风和夏季风相互消长,变化周期长且明显,变化幅度大,表现出10万年的变化周期。     

萨拉乌苏河流域末次间冰阶气候——以米浪沟湾剖面为例

米浪沟湾剖面末次间冰阶层序粒度和化学元素波动韵律与由古流动砂丘砂和上覆河湖相或古土壤构成的沉积旋回颇为一致。古流动砂丘砂犹如现代流动砂丘砂,是东亚冬季风主导下干冷气候的产物;河湖相和古土壤颗粒细化,化学、生物等地球风化程度增强,含较多喜暖的软体动物化石,指示其偏南夏季风主导下的温暖湿润气候。据此,末次间冰阶萨拉乌苏河流域至少经历了10次温湿(W事件)和9次冷干(C事件)气候波动,且可划分为MIS3e(58.85~48.98kaBP)、MIS3d(48.98~39.55kaBP)、MIS3c(39.55~34.59kaBP)、MIS3b(34.59~26.47kaBP)和MIS3a(26.47~23.07kaBP)等5个亚段。其中,19次冷/暖波动可与格陵兰GRIP冰心δ18O冰段/间冰段相对应,5个亚段与我国古里雅冰心在波动性质和相位上都极为一致,与V23-81冷性浮游有孔虫数代表的北大西洋地区气候也具有较好的可比性。谱分析显示出21.70ka、1.05ka、0.64ka、0.50ka等显著周期,即该地千百年尺度气候主要受与北大西洋热盐环流波动引起的东亚冬、夏季风强弱有关,而万年尺度上则受控于岁差周期所导致的太阳辐射变化。     

萨拉乌苏组地层年代学研究

我国北方地区晚更新世河湖相标准地层——萨拉乌苏组地层的年代学研究,有助于正确理解萨拉乌苏组与马兰黄土以及与冰期气候对比等关系。笔者近年来根据野外层位对比和地层沉积相的划分,采用同位素年代测定,并结合黄土-古土壤序列研究的最新成果,初步建立了可以与黄土、深海沉积记录和冰期气候波动对比的萨拉乌苏组地层序列。认为河湖相沉积的萨拉乌苏组形成于约140-70kaBP的末次间冰期,大致与深海氧同位素第5阶段对应,与黄土高原古土壤S₁发育同期。城川组风成细砂形成于约70-10kaBP的末次冰期,与黄土高原的马兰黄土是同期异相地质体.      

石英光释光测年揭示的晚第四纪毛乌素沙地演化

本研究利用石英光释光测年的单片再生法(Single­aliquot Regenerative­dose Protocol,简称SAR)对毛乌素沙地内部西北－东南方向5个风成砂－砂质古土壤剖面进行了年代测定,结合年代框架和剖面沉积相、磁化率及粒度特征探讨了晚第四纪以来毛乌素沙地演化和气候变化。研究表明毛乌素沙地在晚第四纪以来经历了多次沙地固定与活化的交替演化： 距今91.0ka,71.0ka,48.0ka,22.0ka,11.6ka,5.0ka,1.1ka,1.0ka和0.4ka前后风成砂沉积,沙地活化,指示气候干旱,植被覆盖度低; 在距今65ka和全新世适宜期(8.5～5.0ka),沙地固定成壤,砂质古土壤发育,指示气候湿润。另外,剖面中风成砂层数变多、厚度增加、粒径变粗指示了晚第四纪以来毛乌素沙地干旱化趋势加强。     

Groundwater characteristics and climate and ecological evolution in the Badain Jaran Desert in the southwest Mongolian Plateau

The Badain Jaran Desert is the third largest desert in China, covering an area of 50000 km². It lies in Northwest China, where the arid and rainless natural environment has a great impact on the climate, environment, and human living conditions. Based on the results of 1∶250000 regional hydrogeological surveys and previous researches, this study systematically investigates the circulation characteristics and resource properties of the groundwater as well as the evolution of the climate and ecological environment since the Quaternary in the Badain Jaran Desert by means of geophysical exploration, hydrogeological drilling, hydrogeochemistry, and isotopic tracing. The results are as follows. (1) The groundwater in the Badain Jaran Desert is mainly recharged through the infiltration of local precipitation and has poor renewability. The groundwater recharge in the desert was calculated to be 1.8684×10⁸ m³/a using the water balance method. (2) The Badain Jaran Desert has experienced four humid stages since the Quaternary, namely MIS 13-15, MIS 5, MIS 3, and the Early–Middle Holocene, but the climate in the desert has shown a trend towards aridity overall. The average annual temperature in the Badain Jaran Desert has significantly increased in the past 50 years. In detail, it has increased by about 2.5°C, with a higher rate in the south than in the north. Meanwhile, the precipitation amount has shown high spatial variability and the climate has shown a warming-drying trend in the past 50 years. (3) The lakes in the hinterland of the Badain Jaran Desert continuously shrank during 1973–2015. However, the vegetation communities maintained a highly natural distribution during 2000–2016, with the vegetation cover has increased overall. Accordingly, the Badain Jaran Desert did not show any notable expansion in that period. This study deepens the understanding of groundwater circulation and the climate and ecological evolution in the Badain Jaran Desert. It will provide a scientific basis for the rational exploitation of the groundwater resources and the ecological protection and restoration in the Badain Jaran Desert.© 2021 China Geology Editorial Office.     

Climate variability in the Salawusu River valley of the Ordos Plateau (Inner Mongolia,China) during Marine Isotope Stage 3

Fluctuations in climatic proxies of the Milanggouwan section in the Salawusu River valley of the Ordos Plateau (Inner Mongolia, China) during Marine Isotope stage 3 (MIS 3) coincide well with sedimentary cycles for palaeo‐mobile dune sands alternating with fluvial–lacustrine facies and palaeosols. We compared the palaeo‐mobile dune sands with modern mobile dune sands (products of a cold and dry climate dominated by the East Asian winter monsoon), whereas the fluvial–lacustrine facies and palaeosols were controlled by a wet–warm climate similar to that of the East Asian summer monsoon. The MIS 3 climate of the Salawusu River valley appears to have experienced at least nine wet–warm and ten cold–dry fluctuations, divided into five stages: MIS 3e (58 900–49500 yr BP), MIS 3d (49 500–40 700 yr BP), MIS 3c (40 700–36 900 yr BP), MIS 3b (36 900–27 000 yr BP) and MIS 3a (27 000–22 300 yr BP). The 19 cold–warm climatic fluctuations corresponded roughly to the GRIP and Guliyan records, and with fluctuations in the North Atlantic climate. Notable peaks in the spectral analysis occurred at 19 500 yr, 1020 yr, 640 yr and 500 yr. Our results show that the millennial–centennial climate was closely related to the relative strengths of East Asian monsoons, which are controlled by the North Atlantic thermohaline circulation, and which is also closely linked to the Sun's precession period. Copyright © 2008 John Wiley & Sons, Ltd.     

巴丹吉林沙漠南缘冲洪积物的光释光年代及其水文学意义

冲洪积物是古气候和古水文信息的重要记录,为了探讨巴丹吉林沙漠南缘地区全新世气候环境及其对区域地下水的影响,对沙漠南缘的水成沉积物进行了沉积学分析和光释光年代学测试,结果表明本文研究的两个沙漠南缘沉积剖面分别为全新世中期（6.6~5.2 ka）的间歇性河流沉积和暂时性流水形成的洪泛沉积.基于前人全新世中期沙漠中湖泊水位、气候环境重建,以及本文研究的冲洪积物的沉积特征与年代,表明在气候湿润的地质时期巴丹吉林沙漠南缘及山区的区域降水形成暂时性洪流和/或间歇性河流会对沙漠地区地下水进行补给.      

黄土高原黄土物源区的同位素证据

系统采集了黄土高原马兰黄土、河西走廊和青藏高原东北部黄土、河床沙和湖泥样品。用酸淋洗去除方解石后,黄土高原马兰黄土εNd(0)值从-9.2到-11.3,87Sr/86Sr比值从0.71784到0.71944,都落在同位素B区内,与青藏高原东北部、巴丹吉林沙漠和腾格里沙漠的值一致。黄土高原马兰黄土白云石的δ13C值从1.2‰到1.5‰,与青藏高原东北部和河西走廊黄土,巴丹吉林沙漠的白云石的值类似。这些表明青藏高原东北部、巴丹吉林沙漠和腾格里沙漠可能是黄土高原黄土的源区,从而排除了其他沙漠(古尔班通古特沙漠、塔克拉玛干沙漠、毛乌素沙漠、库布齐沙漠、浑善达克沙地、科尔沁沙地和呼伦贝尔沙地)作为黄土物源区的可能性。同位素研究结果和野外调查进一步揭示,黄土高原黄土、巴丹吉林沙漠和腾格里沙漠物质可能最终都是来源于青藏高原东北部。     

Reconstruction of the late Quaternary environment of the lower Luni Plains,Thar Desert,India

Geomorphological processes in the Thar Desert of India are largely climate driven. In the lower reaches of the River Luni (the only major drainage system in the Thar Desert) a fluvio‐aeolian sequence was located at a site called Khudala. Sediments of this sequence represented a variety of depositional environments, namely aeolian, fluvially reworked aeolian, overbank deposits, gravels, and occasional evidence of pedogenesis. This provided a good opportunity to study aeolian–fluvial interaction in the region and for deducing climatic records. From the luminescence dating standpoint these sequences offered a good opportunity for a comparative study of thermoluminescence (TL), blue‐green light stimulated luminescence (BGSL) and infrared light stimulated luminescence (IRSL) on different mineral separates of identical provenance but deposited under different environments. Broadly, within experimental errors, the TL ages agreed with BGSL and IRSL ages on aeolian sands, but differed substantially in the case of fluvially reworked and proximally deposited sands and silts. The sequence provided a record spanning more than 100 ka, with an aeolian phase at > 100 ka, a channel activation phase between 70 and 30 ka and a phase of climate instability between 13 and 8 ka. This appears consistent with the records of monsoon performance during this period, which includes the Younger Dryas. It is also inferred that during the Last Glacial epoch, geomorphological processes in the Thar (both aeolian and fluvial) were dormant largely on account of their relationship with the southwest monsoon. Copyright © 2001 John Wiley & Sons, Ltd.