西藏纳木错晚更新世以来古降水量变化及其环境响应

通过对西藏面积最大(1940km2)和海拔最高(4718m)的大湖-纳木错的调查,发现纳木错周缘有大面积分布的湖相沉积。U系法和14C法测年结果表明,纳木错沿岸湖相沉积的时代为晚更新世和全新世。根据纳木错周缘不同时代湖相沉积物的范围分布的变化,探讨了湖泊演化,计算出纳木错流域古降水量。研究结果,本区自晚更新世以来气候环境由湿润转向干旱,自全新世以来降雨量呈下降趋势。      

西藏纳木错晚更新世以来湖面变化和湖相沉积中粘土矿物显示的环境信息

通过对西藏海拔最高、面积最大湖泊-纳木错周缘湖相沉积、湖岸堤的野外调查和湖岸阶地的水准测量,发现在纳木错沿岸拔湖48m以下,发育有6级湖岸阶地,拔湖48~139.2m发育有高位湖相沉积。湖相沉积物的同位素测年结果表明,纳木错湖泊发育与藏北高原东南部古大湖演化可划分为3个阶段:①116~37kaB.P.间的古大湖期;②37~30kaB.P.间的外流湖期;③30kaB.P.以来的纳木错期。根据纳木错晚更新世以来湖相沉积中粘土矿物的X光衍射分析结果,以及采用比值法、高岭石法和衍射峰法的研究,探讨了粘土矿物所显示的环境变化信息。粘土矿物成分变化表明,该区已具备了寒温带干旱、半干旱区的气候环境特征。为研究青藏高原的湖泊演化、气候变化、古地理变迁及其隆升过程等提供了新资料。      

青藏高原纳木错湖阶沉积的发生特征及环境指示意义

选取的21个湖相沉积物样品分别采自纳木错湖西岸塔吉古日（剖面Nam Co 1）和纳木错湖东北岸的干玛弄附近（剖面Nam Co 2）。按照其发生特征分别将剖面从顶部到底部划分为12个和9个层次,通过分析各个层次沉积物的粒径分布特征、质地组成特点、总有机碳（TOC）、总无机碳（TIC）、总碳（TC）的百分含量、酸度值（pH）、电导率（EC）、含水量等若干环境指示因子。结果显示:无论在比较两个剖面的发生特征,还是环境指示因子特征,剖面Nam Co 1发育程度较剖面Nam Co 2更加发育;通过对测年数据结果分析,两个剖面均形成于晚更新世,并且通过比较各自剖面在垂直方向上的各项环境指示因子的变化趋势,可知纳木错湖流域在晚更新世（约40 ka BP）阶段发生过3次相对明显的冷暖交替过程.     

西藏纳木错末次间冰期以来的气候变迁与湖面变化

在西藏纳木错沿岸,发育了6级湖岸阶地及拔湖48～139.2m的高位湖相沉积.根据湖相沉积的U系法测年和孢粉分析结果,本文探讨了纳木错及邻区末次间冰期(MIS5)以来的古植被、古气候与湖面变化.研究表明,纳木错与邻区的湖面变化可以划分为116～37kaB.P.间的古大湖--"羌塘东湖"期、37～30kaB.P.间的"古纳木错"外流湖-残余古大湖期和30kaB.P.以来的纳木错-藏北湖群期等3大阶段.在MIS5的古大湖阶段,包括纳木错、色林错等藏北高原东南部的众多大、中型湖泊,是互相连通的一个大湖,其范围可能超过了现代的藏北内、外流(怒江)水系的分水岭.在MIS5e末的最高湖面时期,湖面面积可达78800km²,它或许还与藏北高原西南部和中南部的其他古大湖相连,成为面积巨大的网格状深水大湖--"羌塘湖".通过纳木错湖面变化曲线与西昆仑古里雅、格陵兰、南极等冰芯和深海岩芯的氧同位素变化曲线的对比可以发现,全球MIS5的气温要高于末次冰期间冰阶(MIS3),此时藏北高原为气候温和轻爽与湖面最高的大湖期;在末次冰期的两个冰阶(MIS4和MIS2)中,湖面明显下降,邻近的念青唐古拉山发育了小型山谷冰川;而在间冰阶MIS3中,其气候波动的幅度,要比世界其他地区更加明显,湖面波动也较大,特别是36～35kaB.P.间,气温和湿度都较今略高或较高,但不及MIS1中的全新世气候最宜时期的暖湿程度.总之,MIS5和MIS3是亚洲夏季风强烈时期,但前者的强烈程度应大于后者.     

Mineralogy and geochemistry of the Holocene lacustrine sediments in Nam Co, Tibet

The carbonates, clays and major chemical compositions of lacustrine sediments in Nam Co (Lake) were examined by X-ray diffraction, scanning electron microscopy and chemical analysis. Carbonates include monohydrocalcite (MHC, first report from China and in a high-altitude lake), low-Mg calcite and traces of dolomite. MHC in Nam Co is developed in water (1.8 g/L) with high Mg/Ca molar ratios (10.03–15.03), high pH (8.04–9.72) and the presence of bacteria, algae, diatom and ostracoda. Illite and Mg-chlorite provide a strong evidence for physical weathering in the Holocene. Most Ca and Sr in sediments originate from carbonates as the molar ratios of Ca and CO₃²⁻ are all less than 1 and the curve of Sr is very similar to that of Ca. However, most of the Mg, Fe and Rb are from clays. The lake water shifted from a fresh water environment to an evaporative, alkaline environment by 2.06 cal. ka BP. There was a depositional event that the depositional rate changed from 0.134 to 1.639 mm/a at about 2 cal. ka BP.     

A REVIEW OF THE PALEO-HYDROLOGICAL AND GEOMORPHOLOGICAL CHARACTER OF LAKE NAM CO,SOUTH-CENTRAL TIBET

The endorheic Lake Nam Co,south Eastern Tibetan Plateau,was selected to investigate the interrelation between drainage basin processes,especially post-glacial glacier decay,and lake level fluctuations.Landforms of the drainage basin are highly influenced by tectonics,superimposed by fluvial and periglacial processes,and locally by glacial and eolian processes.Thus,geomorphological features and hydrological characteristics were compiled for the lake-basin to provide an overview of the landscape character.Data show that during the Last Glacial Maximum melt water from the mountains accumulated fluvial deposits in the foreland.Concurrently,an increase of the lake level occurred which is presently shown by a cliff line all around Nam Co with its base approximately 29m above the present lake level.The Holocene decrease of the lake level is traced by beach ridges.As Nam Co is an endorheic lake post-glacial water loss has to be primarily explained by evaporation and moisture conditions.However,more detailed conclusions on quantitative and chronological patterns of both factors,melt-water input and evaporation output,still remain to be drawn.     

A REVIEW OF THE PALEO­HYDROLOGICAL AND GEOMORPHOLOGICAL CHARACTER OF LAKE NAM CO|SOUTH­CENTRAL TIBET

Department of Earth Sciences,Freie Universität Berlin,Malteserstraße 74－100,12249 Berlin,Germany)
The endorheic Lake Nam Co,south Eastern Tibetan Plateau,was selected to investigate the interrelation between drainage basin processes,especially post­glacial glacier decay,and lake level fluctuations. Landforms of the drainage basin are highly influenced by tectonics,superimposed by fluvial and periglacial processes,and locally by glacial and eolian processes. Thus,geomorphological features and hydrological characteristics were compiled for the lake­basin to provide an overview of the landscape character. Data show that during the Last Glacial Maximum melt water from the mountains accumulated fluvial deposits in the foreland. Concurrently,an increase of the lake level occurred which is presently shown by a cliff line all around Nam Co with its base approximately 29m above the present lake level. The Holocene decrease of the lake level is traced by beach ridges. As Nam Co is an endorheic lake post­glacial water loss has to be primarily explained by evaporation and moisture conditions. However,more detailed conclusions on quantitative and chronological patterns of both factors,melt­water input and evaporation output,still remain to be drawn.     

塔里木盆地东北部新生代介形类与沉积环境

塔里木盆地东北部库车以东地区下第三系化石罕见。该地区主要为红色含膏盐的粗碎屑岩沉积。中新世以来 ,由于喜马拉雅运动的影响 ,天山不断隆升 ,导致本区加速沉降 ,出现滨浅湖沉积环境 ,介形类逐渐繁盛。中新世中晚期半咸水介形类 Cyprideis爆发 ,广泛出现Cyprideis占绝对优势的半咸水浅湖环境含膏砂泥岩沉积 ,与东邻柴达木盆地阿尔金山以南地区相似。上新世以来 ,本区沉降速率猛增 ,堆积速率更快 ,基本上处于超补偿沉积 ,湖泊大规模萎缩 ,介形类数量锐减。由于喜马拉雅运动晚期的影响 ,天山山脉库车—库尔勒一线以北的山峰不断隆升 ,本区第四纪湖区规模比上新世大大扩展 ,湖泊范围比中新世显著向南迁移 ,Cyprideis再度繁盛并占优势 ,早更新世晚期距今大约不足百万年 ,本区尤其是库南 1井地区 ,除继续出现丰富的 Cyprideis外 ,突然出现淡水 -微咸水介形类 ,形成一个属种多样的高分异度介形类动物群 ,与柴达木盆地南部昆仑山北麓的介形类组合类似 ,主要有 Candona torosa,Candoniella lactea,Candona neglecta,Candona arcina,Cypridopsis vidua,Limnocythereinopinata,Cypris subglobosa,Ilyocypris gibba,Ilyocpyrisbiplicata,Eucyprisinflata,Candoniellaalbicans,Darwinula sp.,Stenocypris sp.等。     

2007-2011年西藏纳木错流域积雪时空变化及其影响因素分析

通过2007-2011年纳木错站人工积雪观测资料,对西藏纳木错流域MODIS两种积雪产品(MOD10A1和MOD10A2)进行了精度验证,分析了纳木错流域积雪累积和消融的空间差异,以及流域积雪覆盖率的时空变化;利用纳木错站人工积雪观测资料及自动气象站资料,分析了纳木错流域积雪要素(积雪深度、雪水当量、积雪密度)的时间变化及其与气候参数(气温、降水量、风速等)的关系.结果表明：纳木错流域MOD10A2数据的积雪识别精度(67.1%)高于MOD10A1(42.2%),总识别精度(73.0%)略低于MOD10A1数据(78.4%).纳木错流域积雪累积和消融存在空间差异,积雪在流域南部的念青唐古拉山脉最先累积,之后为流域东部,最后为流域西部;积雪消融的空间变化则相反.由此导致流域积雪日数南部最大、东部次之、西部及西北部最小.纳木错流域各积雪要素的年内变化存在双峰值特征,峰值分别出现在10-11月和1月,积雪在10-11月受降水和气温共同作用,12月至次年3月主要受气温影响.纳木错流域的平均积雪覆盖率为21.9%,受湖泊效应影响区域(主要为东部地区)达到50.6%,而其他区域仅为18.3%.同时,受湖泊效应影响,纳木错平均积雪深度、积雪水当量均显著大于周边地区.     

西藏纳木错盆地116ka以来沉积演化与青藏高原隆升

根据湖相或湖滨相沉积的铀系等时线年龄测定结果,116kaB.P.以来,在西藏纳木错沿岸,发育了拔湖48m以下的6级湖岸阶地和拔湖48m以上,最高至139.2m的高位湖相沉积.可划分出3个沉积相组合,其演化可划分为4个阶段:①116~72kaB.P.,为深湖环境,古湖面拔湖高于现今纳木错140~48m;②72~37kaB.P.,为半深湖环境,拔湖为48~26m;③37~30kaB.P.,为浅湖环境,拔湖26~19m;④30kaB.P.以来,湖水逐渐变浅,拔湖<19m.纳木错盆地沉积与青藏高原隆升响应关系,揭示出高原自116kaB.P.以来先后经历了稳定期、持续逐步较快隆升期(116~37kaB.P.)、急剧强烈阶段性隆升期(37~30kaB.P.)和较稳定期(30kaB.P.以来).青藏高原的隆升是一个多阶段、不等速和非均变的复杂过程.      

海底水一沉积物界面系统中成矿元素的组合特征与多金属结核形成的关系

利用“海洋四号”调查船HY4—871,881航次在东太平洋海盆取得的底层水、沉积物、间隙水及多金属结核样品,研究探讨了海底水—沉积物界面系统不同物质相中结核主要成矿元素间的关系,并以此为基础讨论了结核成矿元素的来源及其成矿机制。研究表明,Mn、Fc在底层水和沉积物中表现出一定的正相关关系。而在间隙水和结核中则发生了完全相反的变化。间隙水中Mn、Fc密切共生,而结核中Mn、Fc则高度离散,这表明在沉积物早期成岩阶段,Mr~Fc在间隙水中有着相同的溶出富集机制,而在结核形成过程中则有着完全不同的沉淀聚集机制。此外,Co、Ni、Cu与Mn、Fc之间组合关系的变化则反映了不同海底作用的影响。底层水与结核及间隙水与结核相应元素之间关系的变化表明结核主要成矿元素的来源不同,Mn、Ni、Cu主要来源于间隙水,Fc、Co则主要来源于底层水。     

崖19-1-1井晚第三纪浮游有孔虫深度分层及其古海洋学意义

依据ＧｅｒｔａＫｅｌｅｒ和Ｇａｓｐｅｒｉ，Ｋｅｎｎｅｔｔ有关中新世印度洋和太平洋浅层水、中层水和深层水浮游有孔虫深度分层组合的划分模式，对南海琼东南盆地崖１９－１－１井晚第三纪浮游有孔虫作了定量研究，并分析了陆架海区浮游有孔虫不同深度分层组合含量的变化与古地理环境变迁的关系。崖１９－１－１井以浅层水、中层水组合为主，深层水组合不发育，反映本区温跃层不发育，不利深层水浮游有孔虫的生存。滨海区，浮游有孔虫仅为少数几个浅层水的优势种，中层水浮游有孔虫不发育；内浅海区，浅层水浮游有孔虫占绝对优势，中层水浮游有孔虫处于次要地位，所含比例相对较小；外浅海区及陆坡半深海区，浅层水和中层水浮游有孔虫均较发育，中层水浮游有孔虫百分含量相对较高。崖１９－１－１井在上新世早中期曾出现外浅海至陆坡半深海区，为古水深最大时期     

西藏纳木错及邻区全新世气候与环境变化的地质记录

综合分析了全新世期间内的多种与气候和环境变化密切相关的地质记录,结果表明该区全新世期间的气候变化可划分为3个阶段:1)约11.8～8.4kaBP期间,处于微温期和升温期,气候相对温和稍湿.2)8.4～4.0kaBP期间,为全新世气候最适宜时期或大暖期.该期间的平均气温可能比现今高约5℃,降水量比今多100～200mm.3)4.0kaBP以来,气候整体较为干冷.纳木错湖面发生持续下降,其最大下降幅度可达11.4m.冰川进退和湖面波动表明,该期间内的气候波动过程分别与新冰期和小冰期相对应,其中又各包含了3次明显的冷期,其中新冰期期间的最低年平均气温可达-6℃左右.约1970年以来,区域气候向暖湿方向转化,造成念青唐古拉山西布冰川后退约120～200m,纳木错湖面上涨了约2m.     

琼东南盆地晚第三纪浮游有孔虫深度分层意义

依据Ｋｅｌｌｅ１９８５年、Ｇａｓｐｅｒｉ等１９９３年有关中新世印度洋和太平洋浅层水、中层水和深层水浮游有孔虫深度分层组合的划分模式，对南海琼东南盆地崖１３－１－４井晚第三纪浮游有孔虫作了定量研究，并分析了陆架海区浮游有孔虫不同深度分层组合含量的变化与古地理环境变迁的关系。崖１３－１－４并以浅层水、中层水组合为主，深层水组合不发育，反映该区温跃层不发育，不利于深层水浮游有孔虫的生存。滨海区，浮游有孔     

西藏纳木错地区约120kaBP以来的古植被、古气候与湖面变化

西藏纳木错湖相沉积的U系和^11C测年结果表明，湖泊沿岸的6级湖岸阶地及拔湖约48～139．2m的高位湖相沉积形成于约120ka BP以来的晚第四纪。本文根据该套湖相层的发育和其中的孢粉组合特征对纳木错地区约120ka BP以来的湖面变化与古植被、古气候变迁进行了探讨。结果表明，纳木错地区晚更新世以来经历了频繁的湖面波动、气候的冷暖与干湿变化以及森林—草原与草原植被的交替演化。其总体特征是：约115．9ka BP时，纳木错湖面最高。在116～78ka BP期间，该区气候温和凉爽或温和偏湿，植被以疏林草原与森林草原或森林的交替出现为特征，湖面经历了较大幅度的波动，但基本保持在拔湖140～88m之间。在78～53ka BP期间，该区气候干冷，植被以疏林草原为主，湖面大幅度下降，并在拔湖约36～48m之间波动。约53～32ka BP期间，气候转为温暖偏湿或温暖湿润，湖面波动于拔湖约15～28m之间，波动较为频繁。与阶地的发育相对应，该时期内包含了3次明显的暖期和湖面波动过程，区域植被主要以松、蒿、桦为主，为含一定量的冷杉的森林。其中36ka BP左右气候最温暖湿润，区域内可能出现针叶林或针阔混交林。约32～12ka BP期间，该区气候最为干冷，古植被以草原和疏林草原为主，湖面再次发生较大幅度的下降，最低可至拔湖约8m处，但通常维持在拔湖约12～17m之间。约11．8～4．2ka BP期间，气候整体较为暖湿，其中在约8．4～4．2ka BP期间气候最温暖湿润，该区可能发育针叶林或针阔混交林，湖面波动于拔湖2～9m之间，整体波动幅度较小，但波动最为频繁。区域气候对比发现，纳木错地区的冷、暖气候变化过程与整个青藏高原乃至北半球的气候变化基本是一致的，特别是阶地下切所反映的湖面退缩过程与北大西洋的Henrich冷事件之间具有很好的对应关系。     

青藏高原中部2.8Ma以来的化学风化与环境演化的湖泊沉积记录

对采自青藏高原中部错鄂湖泊钻孔近200m以上深处、形成于2.8Ma以来的沉积岩岩芯中Sr,Rb,Zr含量变化及Rb/Sr,Zr/Rb比进行了研究,并结合其岩性、粒度、粘土矿物组成,分析了该地区2.8Ma来化学风化的相对强度和古环境演化过程。研究表明,2.8Ma来青藏高原中部的环境经历了3个演化阶段：在深约197－170m(2.8-2.5Ma)岩性段,低Sr含量,高Rb/Sr和Zr/Rb比揭示的是较弱的化学风化过程,反映了与当时强烈的高原隆升运动有关;在约170－38.5m（约2.5-0.8Ma)段,高Sr含量,低Rb/Sr和Zr/Rb比记录的是该流域较强的化学风化阶段,与高原在稳定期中部总体处于温湿或凉湿的环境下的结论吻合;在38.5-0m（约0.8-0Ma)段,总体Sr含量处于相对低值,Rb/Sr比相对较高,化学风化相对较弱,表明高原中部处于较寒冷的环境之中,高原整体已隆升到4000m以上。     

西藏纳木错沉积物单水方解石出现前后的环境变化

2005年在西藏纳木错水下60m处钻取一支332cm的湖芯,沉积物皆为灰黑-黑色碳酸盐粘土。对湖芯1cm间隔取样并进行X射线、扫描电镜、Sr/Ca和碳酸盐含量的分析。研究发现,纳木错湖底0～258cm沉积物中出现了单水方解石,扫描电镜下该矿物晶形完好,这是个亚稳定矿物,具有重要环境意义。利用碳酸盐含量（24.12%～54.52%）、Sr/Ca比值（<0.006）、方解石中Mg含量（MgCO₃mol%<3.325%）、石膏、粘土矿物（伊利石和镁绿泥石）、单水方解石成因和沉积速率讨论了单水方解石形成前后湖泊环境的变化。2.1cal.kaB.P.单水方解石开始出现,此时纳木错湖水性质推断为pH>8.6,mol Mg/Ca>6.5,Ca²⁺和SO^2-₄离子浓度足以沉淀少量石膏,演化至现代,表层湖水性质为pH=9.4,mol Mg/Ca=10.03～15.03,SO^2-₄浓度较高,Ca²⁺含量低,不足以沉淀石膏。单水方解石出现之前的3.0～2.1cal.kaB.P.时期,沉积速率低（0.134mm/a）,蒸发作用强度不稳定,湖水温度低,矿化度呈上升趋势。该矿物出现后的2.1～1.7cal.kaB.P.时期,沉积速率快（1.639mm/a）,矿化度稳定,气温低,1.8cal.kaB.P.温度达到最低值,为气候冷事件的表现。较快的沉积速率（>1.168mm/a）是纳木错单水方解石形成的重要原因之一,碳酸盐沉积加快和入湖碎屑物质增加是沉积速率加快的主要原因。     

CCA Inferred Environmental Implications of Common Ostracods on the Qinghai-Tibetan Plateau

103 surface sediment samples in 71 water bodies,such as lakes with different salinity,swamps,shallow puddles and rivers on the Qinghai-Tibetan Plateau(QTP),were collected to study the ecological distribution of living ostracods and their environmental implications. Total of 12 genus and 45 species living ostracods are identified. According to the frequencies and abundance of ostracods occurrence,Limnocythere dubiosa,Limnocytherellina kunlunensis,Ilyocypris bradyi,Candona candida,Eucypris rischtanica and Leucocythere dilatata are the common species on the QTP,with occurrence frequency of more than 8 and abundance of more than 570 in the 71 water bodies. Among them,L. dubiosa,occurring in 28 water bodies with 2177 shells,is the most widely distributed ostracod in this research. Canonical Correspondence Analysis(CCA) indicates high correlation between species and environmental variables,suggesting that the occurrence of species is strongly related to the changes in ecological conditions of habitats. Among eight environmental factors,salinity and p H value are the most affective variables that influence the species occurrence. L. kunlunensis is positively correlated with salinity while E. rischtanica is negatively correlated with salinity. C. candida has a positive correlation with salinity,as does I. bradyi although there is not such a strong correlation. L. dubiosa displays a positive correlation with p H value. Consequently,we discuss the environmental implications of the common living ostracods on the QTP based on the CCA as well as the distribution of ostracod species in different salinity and p H values water. L. dubiosa,L. kunlunensis and E. rischtanica are euryhaline species,among which,L. dubiosa is the most adaptable species on the QTP with large occurrence in sundry salinity water and the most widely adaptive range for p H values. L. kunlunensis prefers to saline water while E. rischtanica prefers to fresh water. Both L. kunlunensis and E. rischtanica can live in water from faintly acid to alkaline,in contrast,L. dubiosa only appears in neutral and alkaline water bodies. I. bradyi only occurs in fresh water and oligohaline water with a large p H tolerance range tolerance range from weakly acidic water to alkaline water weakly acidic water to alkaline water. C. Candida lives in freshwater,with p H value above eight. The six common species reach maximum abundance in alkaline water(p H 8-10) except for Ilyocypris bradyi.     

Evolution of an Ancient Large Lake in the Southeast of the Northern Tibetan Plateau

Nam Co is the largest (1920 km2 in area) and highest (4718 m above sea level) lake in Tibet. According to the discovery of lake terraces and highstand lacustrine deposits at several places in Nam Co and its adjacent areas, the authors confirm the existence of an ancient large lake in the southeastern part of the northern Tibetan Plateau. On the basis of the U-series, 14C and ESR dating, coupled with the levelling survey of lake deposits and geomorphology, the evolutionary process of the ancient large lake in the southeastern part of the northern Tibetan Plateau may fall into three stages: (1) the ancient large lake stage at 115-40 ka BP, when the ancient lake level was 140-26 m above the level of present Nam Co; (2) the outflow lake stage at 40-30 ka BP, when the ancient level was 26-19 m above the present lake level; and (3) the Nam Co stage since 30 ka BP, when the ancient lake level was < 19 m above the present lake level. During the ancient large lake stage, a large number of modern large, medium-siz