Grain-size characteristics and climate variability in TMS5e sequence of Tumen section in southern Tengger Desert, northwestern China

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.     

Pollen-based reconstructions of Holocene vegetation and climatic change of Tibetan Plateau

A synthesis of Holocene pollen records from the Tibetan Plateau shows the history of vegetation and climatic changes during the Holocene. Palynological evidences from 24 cores/sections have been compiled and show that the vegetation shifted from subalpine/alpine conifer forest to subalpine/alpine evergreen sclerophyllous forest in the southeastern part of the plateau; from alpine steppe to alpine desert in the central, western and northern part; and from alpine meadow to alpine steppe in the eastern and southern plateau regions during the Holocene. These records show that increases in precipitation began about 9 ka from the southeast, and a wide ranging level of increased humidity developed over the entire of the plateau around 8-7 ka, followed by aridity from 6 ka and a continuous drying over the plateau after 4-3 ka. The changes in Holocene climates of the plateau can be interpreted qualitatively as a response to orbital forcing and its secondary effects on the Indian Monsoon which expanded northwards     

ENVIRONMENTAL EVOLUTION OF ORDOS DESERT IN CHINA SINCE 1.1MA B. P. AS INDICATED BY YULIN STRATIGRAPHICAL SECTION AND ITS GRAIN-SIZE ANALYSIS RESULTS

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…     

水泥固化剂提高风积沙承载性能试验

沙漠风积沙稳定性差, 采用水泥作为固化剂进行风积沙固化, 是改善风积沙性质和实现风积沙资源化利用的有效手段。以取自内蒙古库布齐沙漠的风积沙为材料, 制备3%含水量的重塑风积沙, 掺入水泥固化剂并充分拌匀而形成固化风积沙, 开展水泥固化风积沙的抗剪、抗压和抗拔承载性能试验。结果表明, 水泥掺量对固化风积沙黏聚强度的提高程度要大于内摩擦角。含水量3%的风积沙掺入6%的水泥经28 d常温养护的固化风积沙无侧限抗压强度平均值为0.156 MPa。固化风积沙扩展基础抗拔荷载-位移曲线呈现初始弹性段至峰值荷载以及峰值荷载后破坏的两阶段脆性破坏特征。水泥固化提高风积沙抗拔承载性能效果显著, 且与基础底板尺寸、抗拔埋深及基础深宽比等因素有关。      

THE RECORD OF YOUNGER DRYAS EVENT IN EOLIAN SAND DEPOSIT IN QAIDAM BASIN

DansgaardandothersholdtheviewthatsevereclimaticfluctuationinthelateglacialiscausedbyadjustmentoftheNorthAtlanticcurrent,whichmainlyaffectstheclimateintheNorthAtlanticOCean.ButtherePOrtsabouttheYoungerDryaseventfoundin..varioussedimentsofdifferentplacesprovethatYoungerDryaseventisaclimaticeventoverthegloberatherthanaregion.InrecentyearstherearemanyrePOrtsaboutYoungerDryaleventfoundinmarineandcontinentalsedimentsofmiddlelatitudeinChina.NowitisindubitablethattheYoungerDryaseventexistsinCh…     

Sedimentary facies of the subaqueous Changjiang River delta since the late Pleistocene

The sedimentary facies of the subaqueous Changjiang(Yangtze) River delta since the late Pleistocene was studied based on lithology and foraminifera analysis for two boreholes,CJK07 and CJK11,along with14C dating.Four sedimentary facies were identified,namely fluvial,tidal flat,offshore,and prodelta facies.The fluvial sedimentary facies is comprised of fluvial channel lag deposits,fluvial point bar deposits,and floodplain deposits,showing a fining-upward sequence in general with no benthic foraminifera.A layer of stiff clay overlies the fluvial deposits in core CJK07,indicating a long-term exposure environment during the Last Glacial Maximum(LGM).During the postglacial sea-level rise around 13-7.5 cal ka BP,the tidal flat facies was deposited in core CJK11,characterized by abundant silt-clay couplets.Euryhaline species dominate the subtidal flat foraminiferal assemblages,while almost no foraminifera was found in the intertidal flat.The offshore environment was the major sedimentary environment when the sea level reached its highest level around 7.5 cal ka BP,with a maximum accumulation rate of 10 mm/a found in core CJK11.Prodelta sediments have been deposited in core CJK11 since ~3 cal ka BP,after the formation of the Changjiang River delta.The difference in sedimentary facies between core CJK07 and CJK11 is due to their location: core CJK07 was in an interfluve while core CJK11 was in an incised valley during the LGM.Furthermore,AMS14C dating of core CJK07 shows poor chronological order,indicating that the sediments were reworked by strong tidal currents and that sediment deposited since ~7.7 cal ka BP in core CJK07 was eroded away by modern hydrodynamic forces caused by the southward shift of the Changjiang River delta depocenter.     

Grain-size characteristics of sediments formed since 8600 yr B.P. in middle reaches of Yarlung Zangbo River in Tibet and their paleoenvironmental significance

Widespread aeolian sediments have been found in the middle reaches of the Yarlung Zangbo River, China. The grain-size characteristics of sediments from Cha'er Section in the area were analyzed. The results show that the section include one stratum of paleo-mobile dunes, four strata of paleo-semi-fixed dunes, two strata of paleo-fixed dunes, one stratum of sandy immature soils. The paleo-mobile and paleo-somi-fixed dune sand in this section are similar to modern aeolian sand in either grain-size composition or Mz and σ distribution. Compared the above types of dunes each other, the content of sand substance decreases, while the content of silt and clay increases for palco-fixed dunes and sandy immature soils. Combined with age data for each stratum, the analysis shows that these strata are the products of climate changes and the evolution of aeolian landforms. The evolutionary sequence of the paleoclimate and of acolian activities in the valley since 8600 yr B.P. reveals four stages: 8600-5700 yr B.P., when the paleoclimate was cold and dry, with strong winds, thereby activating dunes; 5700-3600 yr B.P., when it was warm and wet, with weak winds, causing dunes to undergo soil-forming processes; 3600-1900 yr B.P., when climate shifted from cold-dry with strong winds to warm-wet with weak winds, and activated dunes were fixed again; and 1900 yr B.P. -present, when the climate became fine, with weak winds, fixing dunes again.     

“寒亭组”是山东唐宋时期两期洪水的产物——基于沭河沙带调查及光释光测年研究

对分布于临沂一带沂河与沭河沿岸沙带的展布形态与沉积层理进行研究,认为该沙带属于古洪水期滞留沉积物(SWD),并非以往认为的风沙成因(寒亭组)。为了获取滞留沉积物的形成年龄,采用光释光测年(OSL)方法,首次获得对应沉积物年龄为0.8ka,1.2ka,结合相关历史时段的洪水记录,综合分析后,认为该滞留沉积物记录了发生在唐宋时期的两次历史洪水。     

Late Pleistocene aeolian activity in Haitan Island,Southeast China: Insights from optically stimulated luminescence dating of coastal dunes on marine terraces

The 'Old Red Sand' is a type of semicemented medium-fine sandy sediment that is red (10R4/8) or brown red (2.5YR4/8) in colour and is found in late Quaternary deposits. The sediments have distinctive characteristics and are a critical archive for understanding climatic changes in the coastal areas of East Asia. The ages of the late Quaternary aeolian sand dunes from Haitan Island in the coastal area of South China are still in debate. In this study, three sets of marine terraces were identified in the northern region of Haitan Island. Aeolian dune sands are well preserved on the top of these terraces. Quartz Optically Stimulated Luminescence dating and the distribution of the formation ages demonstrated that the palaeo-dunes are deposits from the middle-late period of the Late Pleistocene (Q ₃ ^2-3 ). The period may be divided into three stages, 100–90 ka, 70–60 ka, and 40–20 ka, in which the palaeo-dunes of the first two stages are more widespread and were formed separately during a low-sea level period of the Marine Isotope Stages 5b and 4. Several depositional palaeo-flood event records were preserved during the last stage due to the increasing gradient of mountain gullies formed during the Last Glacial Maximum.     

西宁的黄土研究

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。     

粒度端元记录的靖边地区MIS 3以来的气候变化

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。      

A METHOD TO ESTIMATE PALEOTEMPERATURE FROM ENVIRONMENTAL PROXIES IN LAKE SEDIMENTS——A STUDY ON ZOIGE BASIN IN EASTERN TIBETAN PLATEAU, CHINA

Seeking for an effective method to probe further the relation among Tibetan Plateau, climatic events, and natural environmental changes in the Zoige Basin, we proposed a physical model for the reconstruction of climate and environment and a preliminary application was conducted on the 45 m (about 200 ka BP), upper part of Core RM (310 m long) drilled in the Zoige Basin (33°57’N, 102°21’E), on the eastern Tibetan Plateau. The results showed that: a) in the Zoige region, the maximum temperature in the period equivalent to Stage 7 in the deep-sea stable oxygen record was 2.7°C higher than that at present; b) Stage 6 temperature was 4.3°C lower than that at present; c) Stage 5 peak temperature was 5.2°C higher that that at present; d) Stage 4 average temperature should have been 2–3°C lower than that at present; and e) Stage 3 temperature differences within the period were more than 4°C. It was found that during Stage 6 (140–160 ka BP) the environment in the Zoige Basin was extraordinary, representing a transition period from warm-dry and cold-wet to warm-wet and cold-dry environmental conditions due to the uplift that occurred on the Tibetan Plateau at this period. Project 49803001 supported by NSFC and also funded by National and CAS Tibet Research Project (G1998040800).     

陕西榆林风沙滩区全新世气候和环境变迁

榆林长城沿线处于环境变化敏感带,其风沙滩区沉积剖面的磁化率和粒度分析结果显示,该区全新世早期11 500~10 000 a BP随着全球气候的逐渐转暖,磁化率、黏粒和粉沙含量逐渐增高;全新世中期的10 000~4 500 a BP气候相对比较湿润,植被覆盖度增大,风沙活动减弱,地表沉积物当中粉沙和黏土成分含量显著增大,风化成壤作用增强,地表发育沙质弱古土壤;全新世中期后段的4 500~3 000 a BP期间,气候以比较温和湿润为主,但在4 200~4 000 a BP出现一个气候干旱事件,风沙活动强烈;近3 000 a以来,气候显著干旱化,波动频繁,地表风沙沉积物显著变粗,表现出有5次沙漠扩张。该区生态环境演化、人文历史变迁基本上是自然因素与人为活动综合作用的结果,以自然演化为主,近代人为因素对环境变化起着加强和放大作用。     

Response of river terraces to holocene climatic changes in Hexi Corridor, Gansu, China

ＲＥＳＰＯＮＳＥＯＦＲＩＶＥＲＴＥＲＲＡＣＥＳＴＯＨＯＬＯＣＥＮＥＣＬＩＭＡＴＩＣＣＨＡＮＧＥＳＩＮＨＥＸＩＣＯＲＲＩＤＯＲ,ＧＡＮＳＵ,ＣＨＩＮＡ①ＬｉＹｏｕｌｉ（李有利）ＹａｎｇＪｉｎｇｃｈｕｎ（杨景春）ＤｅｐａｒｔｍｅｎｔｏｆＧｅｏｇｒａｐｈｙ...     

苏北盆地张家垛油田阜三段储层特征及主控因素

利用岩心观察、铸体薄片、扫描电镜及阴极发光等,研究苏北盆地张家垛油田阜三段.结果表明:该储集层岩石类型主要由泥岩、粉砂岩及薄层细砂岩组成;砂泥岩呈互层分布,存在大量泥质条带和生物扰动构造,其中以泥岩、粉砂岩最为发育;粒间溶孔、粒内溶孔、杂基内微孔隙是主要孔隙类型,其中粒内溶孔最为发育;研究区为浅湖亚相沉积,发育坝砂、滩砂和浅湖泥沉积微相,沉积相带、成岩因素是影响研究区储集层物性的重要条件.阜三段储层主要以坝砂为主,其次是滩砂;坝砂粒度较粗,杂基含量低,粒间孔、溶孔发育,砂体厚度大,储集性能好,而滩砂粒度较细,杂基含量高,微孔发育,胶结作用弱,砂体厚度薄,物性相对较差.     

Characteristics of Sand Dune Pattern and Fluvial-aeolian Interaction in Horqin Sandy Land,Northeast Plain of China

The interaction between fluvial and aeolian processes can significantly change surface morphology of the Earth. Taking the Horqin Sandy Land as the research area and using Landsat series satellite remote sensing images, this study utilizes geomorphology and landscape ecology to monitor and analyze the aeolian geomorphology characteristics of the Horqin Sandy Land. Results show that the sand dunes of the Horqin Sandy Land are mainly distributed on alluvial plains along the banks of the mainstream and tributaries of the Western Liao River, and the sand dune types tend to simplify from west to east and from south to north. The aeolian geomorphology coverage tend to be decreasing in the past 40 years, with an average annual change rate of 0.31%. While the area of traveling dunes decreased, the area of fixed and semi-fixed dunes increased. The fractal dimensions of various types of sand dune have all remained relatively constant between 1.07 and 1.10, suggesting that they are experiencing a relatively stable evolutionary process. There is a complex interaction between fluvial and aeolian processes of the Horqin Sandy Land, which plays a central role in surface landscape molding. Sand dunes on both sides of different rivers on the Horqin Sandy Land present certain regularity and different characteristics in terms of morphology, developmental scale, and spatial pattern. There are six fluvial-aeolian interaction modes in this area: supply of sand sources by rivers for sand dune development, complete obstruction of dune migration by rivers, partial obstruction of dune migration by rivers, influence of river valleys on dune developmental types on both sides, influence of river valleys on dune developmental scale on both sides, and river diversion due to obstruction and forcing by sand dunes. This study deepens our understanding of the surface process mechanism of the interaction between fluvial and aeolian processes in semi-arid regions, and provides a basis for researches on regional landscape responses in the context of global environmental change.     

Environmental evolution of Gongwang Mountains during Holocene in northeastern Yunnan, China

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.     

Grain-size characteristics of sediment in Daniugou peatland in Changbai Mountains,Northeast China: Implications for atmospheric dust deposition

The grain-size distribution characteristics and grain-size parameters of sediment in two vertical sections of Daniugou peatland in the Changbai Mountains were systematically investigated. A comparative analysis of the sediment granularity using a discriminative function with Hongyuan peat, red clay, loess-paleosol, fluvial deposit as well as lacustrine deposit was also conducted. It turns out that the vertical section of Daniugou peat ash is primarily constituted by clay and silt particles, and the content of sand is relatively small. Grain-size frequency curves generally show a single-peak modality while a bimodal pattern is detected in the upper layer. The grain-size component and peak pattern of grain-size frequency curves also illustrate that peat ash materials were transported to the peatland by long-range aeolian dust during the deposition process, while there existed short-distance dust influence in peat deposition of the upper layer. Comparisons of grain-size parameters and the discriminative Y-value of Daniugou peat ash with those of typical aeolian sediments show close similarities, suggesting the possibility that atmospheric dust transport processes were involved in the accumulation of peat again. Moreover, the variations of grain-size distribution suggest the local environmental deterioration which is just the driving force of local dust elevation. Grain-size analysis of peatland sediment is demonstrated to be one effective method to extract information about regional and global environmental evolution, and more attention should be paid to current local ecological environment and to seeking a balance between economic development and environmental protection in Northeast China.     

土工格室加固风积沙路基不同深度动力响应试验研究

风积沙路基的处理一直是沙漠公路建设面临的难题, 土工格室加固方法可为沙漠公路建设提供一条新路径, 结合S21线(乌鲁木齐-阿勒泰)沙漠公路路基现场试验, 研究不同路基深度动力响应特征, 对土工格室加固风积沙性能探究具有重要的价值及意义。结果表明: ①测试车速对路基不同深度处动应力、动加速度和动速度的时程曲线波动性影响较大, 且提高车速时, 动速度峰值、动加速度峰值和动应力峰值都出现了明显的增加; ②随着路基层深度的不断增加, 动速度幅值、动加速度幅值和动应力幅值均呈现出逐渐衰减的趋势, 其中在土工格室加固风积沙层衰减幅度最大; ③沿路基横断面水平方向上, 动速度幅值、动加速度幅值和动应力幅值均呈指数型衰减的趋势, 距振动源水平距离为5 m时, 其幅值衰减至10%左右, 可将此水平范围作为工程设计参考值。      

Progress in studies on geographical environments of the Qinghai-Xiang plateau

The Qinghai-Xizang (Tibet) Plateau area was subjected to twice uplift and planation in the Tertiary. Intense uplifting of the plateau area has given rise to drastic changes and differentiation of physical environment on the plateau and the surrounding area since 3.4 Ma B.P. Significant environmental changes with dry tendency in interior of the plateau had occurred during the last 150 ka B.P. By comparative study on several mountains of the plateau, two systems of the structure-type of the altitudinal belt are identified and nine groups are subdivided. A distribution model with close relevance to highland uplift effect has been generalized. A number of striking geo-ecological phenomen and their spatial pattern such as moisture corridor, dry valleys, high-cold meadow zone, and high-cold arid core area are investigated and discussed. Based on the thermal conditions, moisture regimes and variation in landforms of the plateau is sequentially demarcated. A tentative scheme of 2 temperature belts, 10 natural zones and 28 physical districts has been proposed not including southern slopes of the East Himalayas. The Qinghai-Xizang Plateau is sensitive to “green house effect”, showing close relation with global change. Characteristics of temperature and precipitation on the plateau during the last 2000 years, and response of glaciers, snow deposit and permafrost on the plateau to global change are dealt with in the present paper. Under the auspices of Chinese National Key Project for Basic Research (G1998040800) and CAS project on the Qinghai-Xizang Plateau (KZ951 - A1 - 204, KZ95T - 06)