Seven million-year iron geochemistry record from a thick eolian red clay-loess sequence in Chinese Loess Plateau and the implications for paleomonsoon evolution

Recently, the Tertiary red clay sequence underlying Pleistocene loess has attracted much attention. The remarkable progress is the recognition that the Tertiary red clay sequence is also wind-blown in origin, thus providing a good opportunity to reconstruct long-term monsoon changes. In contrast to the loess deposits, the magnetic susceptibility and the pedogenic characteristics are almost independent of each other in the red clay, thus challenging the validity of the readily measurable magnetic susceptibility in describing the monsoon history recorded by the red clay. With the objective to address the long-term East Asia summer monsoon evolution, the free to total Fe₂O₃ ratios were calculated in a continuous eolian red clay-loess sequence at Lingtai, the Chinese Loess Plateau, which has a thickness of 305 m and a basal age of 7.0 Ma. The seven million-year Fe₂O₃ ratio record from the red clay-loess sequence indicates that (ⅰ) variations of the free to total Fe₂O₃ ratios of the loess can correlate generally with the alternations of the loess and paleosol horizons; (ⅱ) the East Asia summer monsoon was stronger as a whole in Neogene than that in Quaternary; (ⅲ) the strongest East Asia summer monsoon may occur between 4.0 and 4.8 Ma. The relatively small ice volume and high global temperature may be responsible for the strong summer monsoon during the early Pliocene.     

毛乌素沙地上空沙尘暴的前向轨迹及其影响范围

基于气象数据、MODIS遥感影像数据和NCEP再分析资料, 利用HYSPLIT模型模拟2000—2019年毛乌素沙地上空不同海拔高度(500, 1000和1500 m)各季节沙尘暴的前向轨迹, 并与遥感影像识别出的沙尘信息进行比较, 识别毛乌素沙地沙尘暴的影响范围。结果显示: 1) 在过去的20年中, 共有143个沙尘暴月和387个沙尘暴日, 并且 2004 年以来, 毛乌素沙地发生沙尘暴的频率逐渐降低; 2) 季节性气候条件对毛乌素沙地沙尘暴的移动路径有很大的影响, 春季沙尘暴发生频率较高, 秋季发生频率最低; 3) 受毛乌素沙地沙尘暴影响的国内地区主要包括陕西省北部、山西省北部、河北省北部和中部、山东省北部和中部、北京市、天津市、内蒙古自治区东部以及东北三省, 国外受影响的地区有朝鲜、日本北部以及俄罗斯与我国交界处, 受影响的海域有渤海、黄海北部和日本海西北部。遥感影像与HYSPLIT模型的比较提供了一种对沙尘运输、扩散和沉积过程进行验证和加深了解的有效工具, 研究结果可以为防灾减灾决策及沙源地治理提供科学的参考依据。     

萨拉乌苏河流域全新世气候变化的元素地球化学记录

通过对萨拉乌苏河流域滴哨沟湾左岸沉积剖面常量元素Si、Al、Fe、Ca、Mg、K、Na含量及其比值变化的分析,结合~(14)C测年结果及粒度、有机质指标,并综合已有研究,探讨了该地区全新世以来的气候变化.研究表明,9.6ka BP前气候干冷,沉积相为风成沉积;9.6~8.4ka BP气候由干冷向暖湿转变,期间存在干冷波动;8.4~4.0ka BP进入全新世大暖期,其中,8.4~6.5ka BP为全新世大暖期的鼎盛时期,降水增加,积水成湖,湖泊水位高且稳定;6.5ka BP气候发生明显转变;6.5~4.0ka BP湖泊水位逐步下降形成富含螺壳的浅水环境,但气候整体仍较为湿润;4.0~1.2ka BP气候变干冷,发育沼泽;1.2~0.7ka BP气候转暖湿,沉积相由沼泽相转变为湖泊相;0.7~0.5ka BP为河流相沉积,气候较为干冷.剖面记录的气候变化可与东亚季风变化、温度变化、太阳辐射进行对比,反映了该区域气候变化与全球气候变化的一致性.     

Distribution of sand dunes and sand shifts along the southern fringe of the Mu Us Desert since the Ming Dynasty

This article takes the two segments of the Ming Great Walls, Dabian and Erbian, and their associated barracks and forts as geographical references. Based on a detailed scrutiny of historical records of the Ming and Qing dynasties, and on field surveys, the southern boundaries of the sand dunes and sand shifts of the Mu Us Desert in the Ming and Qing dynasties are carefully reconstructed. A comparison of the southern boundaries of the sand dunes and sand shifts of the Mu Us Desert in Ming and Qing with the modern boundary revealed in remote sensing imagery clearly shows that the southern boundary of dunes and shifts in the Mu us Desert has expanded only in a few areas and on a small scale. In the area to the south of Changle Fort, along the direction of annually prevailing winds, sand drifts have penetrated through the Jialu River valley into the loess region and have formed a sand strip of 32 km long and 3 km wide. To the east of Qingping Fort, sand drifts penetrated toward the eastern loess region through the Luhe River valley and have formed another sand strip of 8 km long and 2 km wide. Generally speaking, though the intensity of human activity has been increasing in this area since the Ming Dynasty, the Mu Us Desert has not significantly expanded toward the southeast or southwest. The sand-loess boundary in the southern fringe of the Mu Us Desert has been almost unchanged since the Ming Dynasty.     

Validating a dust production model by field experiment in Mu Us Desert, China

It is essential for validation and improvement of a dust production model to perform field observations on dust emissions. The dust production model (DPM model) consists of two physically explicit sub-models, namely saltation model [1, 2] (eq. (1)) and sandblasting model [3] (eqs. (2) and (3)). Fh is saltation flux, E is fraction of erodible surface, C is a dimensional constant, ρa is air density, g is gravitational acceleration, U* is the wind friction velocity, Ut*(Dp) is threshold frict…     

Eolian sand deposition and its environmental significance in the northeastern margin of the Qinghai-Xizang Plateau

The dry climate which appeared about 8#x2013;7 Ma ago in South Asia has been interpreted as results of the intensification of Asian monsoon caused by the uplift of the Qinghai-Xizang Plateau at its maximum altitude around that time. Whether it is or not, it is a critical problem. A total of 55 samples were taken from the Tertiary red earth and Quaternary lacustrine deposits and loess in the Linxia Basin which is located in the northeastern margin of the Qinghai-Xizang Plateau, for the analysis of quartz types and contents using electron probe microanalyzer. The results indicate that the eolian sands have existed since 15Ma and reached its maximum content at 8 and 6#x2013;5 Ma, respectively. This means that the climate was very dry during 8-5 Ma period in western China, which was regarded as the result of global climatic change at that time. Mean size of quartz sand grains was about 0.4 mm during 15#x2013;3.6/2.6 Ma period and dropped to 0.1–0.07 mm dramatically after 3.6–2.6 Ma. This demonstrates that the local eolian deposition was decreased significantly and even disappeared since Late Pliocene and was replaced by dust deposits from distal source, suggesting the uplift of Qinghai-Xizang Plateau and the change of air circulation after 3.6–2.6 Ma.     

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.     

远源地下水入侵阿拉善高原沙漠:酸溶物Sr同位素证据

选取北方西－东向气候剖面上物质组成相似的四个沙漠（塔克拉玛干、巴丹吉林、腾格里和毛乌素）,测定其地表沙酸溶物87Sr/86Sr比值、Ca2+和Sr2+浓度。Ca2+和Sr2+浓度相关性极好,在降雨量低的塔克拉玛干沙漠中最高,向东逐渐降低,在降雨量多的毛乌素沙漠中最低。降雨量是控制阳离子浓度变化的主导因素。酸溶物87Sr/86Sr比值在四个沙漠中有不同于阳离子变化的区域特征。塔克拉玛干沙漠酸溶物87Sr/86Sr比值在0.71以下,巴丹吉林和腾格里沙漠的大于0.7112,而毛乌素沙漠的在0.71-0.7112之间变化。塔克拉玛干和毛乌素沙漠地表沙酸溶物87Sr/86Sr比值仅受气候变化的制约。巴丹吉林和腾格里沙漠除了受气候因素影响外还受其它因素的制约,最可能的就是远源地下水。经计算,远源地下水对巴丹吉林沙漠的影响份额为47%,对腾格里沙漠为44%,接近气候因素的影响。     

近50年来毛乌素沙地草地生态脆弱性评价——以内蒙古乌审旗为例

选择位于毛乌素沙地腹地的乌审旗作为研究区,基于1960年代,1978,1988,2000和2008年土地覆被数据,借助GIS空间分析技术,通过建立＂敏感性-弹性-压力＂生态脆弱性评价模型,对研究区近半个世纪的草地生态脆弱性进行动态评价。结果表明：乌审旗草地生态系统大部分属于中、低度脆弱区。50年间,草地生态脆弱性经历了...     

Loess in the Tian Shan and its implications for the development of the Gurbantunggut Desert and drying of northern Xinjiang

Eolian loess is widely distributed on the various geomorphic surfaces between 700–2400 m a.s.l. on the northern slope of the Tian Shan. It is formed in a synchronous manner with dust transported from the Gurbantunggut Desert in the Junggar Basin. The thickest section of loess was found in the Shawan and Shihezi regions. Paleomagnetic and climatic proxy analyses of over 71 m of a loess-paleosol sequence on the highest terrace of the Qingshui He (River) in the Shawan show that the paleomagnetic Bruhues/Matuyama (B/M) boundary lies at the bottom of paleosol S8, at a depth of 69.5 m, and the bottom of the sequence was estimated to be ∼0.8 Ma. This implies that the extremely dry climatic conditions in the Junggar Basin and the initial Gurbantunggut Desert were present at least by 0.8 Ma. High-resolution grain size series demonstrate that this area and desert expansion experienced two dramatic periods of desert expansions that occurred at ∼0.65 Ma and 0.5 Ma, respectively; and the subsequent continuous enhancement led to the environment presently observed. This tremendous environmental effect, caused by large-scale expansion of the desert and arid region of inner Asia, might be an important driving force for the global temperature drop that occurred in the mid-Pleistocene.     

Variations of geochemical compositions and the paleoclimatic significance of a loess-soil sequence from Garzê County of western Sichuan Province, China

The West Sichuan Plateau is located in the southeast margin of the Tibetan Plateau, where the climate is mainly influenced by the Indian southwest summer monsoon and the Tibetan Plateau monsoon. In this study, detailed geochemical analysis has been carried out on Ganzisi loess-paleosol sequence in Ganzê County of western Sichuan Province. The results indicate that Ganzê loess and paleosol have experienced the incipient stage of chemical weathering in dust source regions, characterized by the decomposition of plagioclase which caused the depletion of mobile elements Na and Ca. The post-depositional chemical weathering is characterized by carbonate dissolution and oxidation of Fe2＋. The variations of some geochemical indexes （such as CIA values, Na/K and Fe2＋/ Fe3＋ ratios） in Ganzisi loess-paleosol sequence indicate a gradually decreased chemical weathering intensity in the dust source regions and deposition areas since 1.15 Ma BP consistent with the general increase of global ice volume, reflecting that the arid trend since 1.15 Ma BP in the southeast Tibetan Plateau is a regional response to the global climate change. The geochemical indexes in this section also reveal an obvious drying step occurred at about 250 ka BP in this region. We interpret this drying step as a result of decreased influence of the Indian southwest summer monsoon. This decrease in monsoon moisture is probably attributable to the uplift of the southeast margin of the Tibetan Plateau at about 250 ka BP.     

Arbuscular mycorrhizal fungi associated with the clonal plants in Mu Us sandland of China

Clonal plants in Mu Us sandland change the sandy enviroment. The clonal plant is a kind of resource in restoration of the Mu Us sandy landscape. Soil samples at depth of 50 cm in the rhizosphere of the clonal plants were collected in 4 replicates at each location and divided into sections corresponding to 0—10, 10—20, 20—30, 30—40 and 40—50 cm depths in two representative sites from north to south in Mu Us sandland, northwestern China, in July 2005. Clonal plants included Psammochloa villosa and Hedysarum laeve. The colonization and ecological distribution of arbuscular mycorrhizal (AM) fungi were investigated in the rhizosphere of clonal plants in Mu Us sandland. The results showed that the clonal plants established well symbiosis with AM fungi; AM fungal species and spatial distribution were significantly related with the host plants and soil factors. Of 16 AM fungal taxa in three genera isolated and identified, Glomus multicaule was only observed in the rhizosphere of Psammochloa villosa; Glomus aggregatum, Glomus hydembadensis, Glomus constrictum and Acaulospora rehmii only appeared in the rhizosphere of Hedysarum leave. The depth of soil layers observably affected the spore density and the frequency of colonization (%F). The maximal %F and spore density occurred in the 10—20 cm layer at the site of Ordos Sandy Land Ecological Station, but which occurred in the 0—10 cm layer in Shanxi Yulin Rare Sandy-plants Conversation Field. AM fungal status and colonization might be used to monitor desertification and soil degradation.     

Terrestrial mollusk evidence for the origin and sedimentary environment of the Late Tertiary Red Clay Formation in the Loess Plateau, China

The origin and sedimentary environment of theLate Tertiary (Neogene) Red Clay Formation in northernChina had long been controversial. A new mollusk recordfrom the Xifeng red clay (red-earth) sequence in the centralLoess Plateau provides the biological evidence for addressingquestions of its origin and environmental implication. Thestudy of composition and preservation condition of seventymollusk fossil assemblages reveals the initial ecological con-dition of the red clay formation, avoiding the effect ofpost-deposited alteration. The result shows that all of identi-fiable mollusk species are composed of terrestrial taxa, mostof them are the common species found in the overlying Qua-ternary Ioess-paleosol sequence. Most of fossil individualspreserved in the red clay strata are in living conditions basedon the investigation of fieldwork, indicating the originalpopulation. Thus, the mollusk fossil assemblages can be usedas an indicator of primary environment of the red clay for-mation. The mollusk record from the Xifeng red clay se-quence supports the view that the red clay is an aeolian ori-gin, similar to the overlying Quaternary loess deposits. Ourdata also reveal the history of environmental changes atXifeng from 6.2--2.4 Ma, which is coupled in phase with theformation and development of the Arctic ice sheets and theprocess of the Tibetan Plateau uplift. Both may be the majorcause and forcing mechanisms of the late Tertiaryenvironmental changes in the Loess Plateau.     

Age and genesis of the Shagou River terraces in eastern Qilian Mountains

The fluvial terrace sequence in eastern Qilian Mountains is a record of periodic uplift events of the Tibetan Plateau. Based on paleomagnetic dating, thermolumines-cence dating, radio carbon dating and loess-paleosol sequence on terraces, we preliminarily determine the ages of five major terraces of the Shagou River, northern side of the Qilian Mountains. The ages of five terraces were about 830, 418, 250,140 and 10 ka, respectively. Analysis on characteristics of terraces show that five major terraces were mainly tectonic genesis. Therefore, five major terraces recorded five strong rising events in the Qilian Mountains during the past 830 ka. The ages of those rising events are about the same as those terraces formation. Sub-terraces, constituting a main terrace, were perhaps mainly formed by climatic changes.     

天水盆地古近纪地层年代及其意义

天水盆地位于青藏高原东北缘六盘山与西秦岭二重要构造带交汇处,该盆地充填的新生代沉积序列记录着该区构造变形历史,因此研究该盆地沉积记录对探讨青藏高原东北缘新生代构造活动事件具有重要意义.通过对天水盆地古近纪砾石层砂质透镜体中碎屑颗粒磷灰石裂变径迹热年代学研究,获得样品地层的最大沉积年龄为24.8士1.5 Ma.结合前人的工作,厘定该套古近纪地层最顶部地层年龄为22～24.8 Ma,并确定天水盆地古近纪沉积物源区在24.8 Ma左右发生了构造冷却事件,推断印度板块与欧亚大陆碰撞的远程效应在古近纪末-新近纪初已传递到青藏高原的最东北缘.     

Carbon isotopic records in paleosols over the Pliocene in Northern China: Implication on vegetation development and Tibetan uplift

Carbon isotopic composition of pedogenic carbonate can be used to estimate the proportion of C₄ and C₃ plants. Here we present carbon isotopic data of carbonate in a red earth section at Xifeng, central Loess Plateau. Results show that C₄ vegetation increased in ∼4.4 Ma B.P., stabilized between 4.0 and 3.0 Ma B.P. The character and timing of C₄ expansion on the Loess Plateau are similar, but different with other localities, e.g. Pakistan and Africa, implying that regional climate changes were main factors driving the expansion of C₄ plants. This event is comparable in timing with increased aridity evidenced by Xifeng grain size and North Pacific eolian dust records. Therefore we argue that the Pliocene expansion of C₄ plants in northern China might have been caused by the increased aridity, which in turn might be related to rapid uplift of the Tibetan Plateau.     

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.     

蒙陕交界地区风沙活动规律及其防治

在描述库布齐沙漠和毛乌素沙地沙丘基底地形之后，分析了流动沙丘分布规律与基底地形的关系。在明确沙地形成时代概念的基础上，论证了该沙漠与沙地分布范围上的稳定性，库布齐沙漠为扩展型的，毛乌素沙地属稳定型的。库布齐沙漠的风沙危害包含了直接与间接危害２种类型；毛乌素沙地风沙危害主要是沙丘再流动，有３种危害途径，最后，根据毛乌素沙地沙丘分布规律，分析了引起沙丘再流动的人为因素和自然因素，及其各自所占的比重。     

Pollen evidence from Baode of the northern Loess Plateau of China and strong East Asian summer monsoons during the Early Pliocene

The red clay eolian sequence on the Chinese Loess Plateau (CLP) is an important archive for paleoclimate change from the late Miocene to Pliocene,and can provide significant information for the controversial problems of East Asian monsoon evolution and its forcing mechanism.In this study,we present a pollen record from Baode,northern CLP.The record shows four stages of paleoecological evolution.From 5.6-4.4 Ma,a forest steppe ecosystem developed under an extremely warm period with high seasonal precipitation.Since 4.4 Ma,a drier episode occurred,which prompted parkland landscapes to develop.During 3.5-3.05 Ma,the environment changed to a rather open steppe ecosystem with a much cooler and drier climate.After 3.05 Ma,the vegetation evolved to forest steppe.Using the percentages of arboreal plants to mirror precipitation,and comparing with other published pollen data from the CLP,we find the existence of S-N directionality of the precipitation change and high percentage of arboreal plants in the entire CLP during the Early Pliocene,which suggest the CLP was characterized by a strong East Asian summer monsoon.The strong summer monsoon corresponds well to the low global ice volume,which may illuminate global climate mechanism for the summer monsoon evolution in the early Pliocene.     

Reconstruction of the spatial patterns of desert/loess boundary belt in North China during the Holocene

The desert/loess boundary belt is the transi-tional region between desert and loess, where aeolian sandand loess interlock in space and alternate in time. It, being seriously unstable in space-time, sensitive to climatic changes and with fragile ecological environment, is an ideal region for studying the global climate change. There are deposi-tional sequences of paleosol with sub-horizontal interbedded aeolian sand and loess, and the stratigraphical evidences show that there widely exist 3—4 layers paleosol in sand lands of northeastern China, 4—5 layers in Mu Us Sandy Land and Hunshandake Sandy Land, more than 4 layers in the Qinghai Lake region and the Gonghe Basin of Qinghai Province during the Holocene. These indicate that the desert has experienced several times of extending and compacting, along with which the desert/loess boundary belt vibrated. It possesses good coherence with global climate change and eustasy. The coherence shows that the monsoon change in East Asia is the primary driving factor for the swing of desert/loess boundary belt. Besides, human influence con-stantly intensified the swing of the belt, especially in the south of Mu Us Sandy Land during the 2000—3000 aBP.