西藏台错古生物记录的古环境事件及硅藻、介形虫化石新发现

在厚度为369cm的台错TT-1剖面中,共采取连续样品156个,单样平均厚度仅为2.36cm,使之成为一个理想的进行高分辨率研究的对象。通过对样品的硅藻研究,以及全部样品的孢粉和介形虫化石分析鉴定,本项研究取得了多项创新研究成果。①结合铀系不平衡法获得的准确可靠定年数据,本文重建了西藏台错古湖区自晚更新世晚期以来的古气候、古环境演变。从万年尺度上,台错在>32.60～26.15ka BP间的6.45ka间长期处在潮湿、湿润的环境之中;在26.15～4.50ka BP的21.65ka间,气候则以偏干和寒冷为大背景;在4.50ka BP,沉积记录终断,表明湖泊干枯消失。从百年-千年尺度上,厘定出台错自22.70ka BP以来,经历了明显的寒冷气候事件8起,湿润气候事件3起,以及气候颤动事件2起,从而更加详尽地描述了台错在18.2ka中经历的19个古环境、古环境演变阶段。②首次发现了两种硅藻的新化石种--西藏胸隔藻属新种Mastogloiatibetica Li et Wei和西藏桥弯藻属新种Cymbellataicuonensis Li et Zheng。③首次在西藏境内大量发现了Cyprideis torosa(结节正星介)和C.littoralis(滨海正星介)。本文为全球气候变化研究及青藏高原的古气候、古环境研究,提供了来自高原内部的全新精细记录和科学依据。     

西藏台错古湖沉积物中的硅藻及其古环境

根据硅藻组成、丰度及其生态特征的研究，可以恢复西藏台错古湖地区的古气候演变：在17．8～16．0kaBP经历了气候严寒期；16．0～13．9ka BP为回暖期；在11．5～10．7ka BP气候发生波动性变化，从较暖湿期到寒冷干旱的新仙女木期；在10．4～9．0ka BP气候略有变化，但总体上仍处于寒冷干旱期；在9．O～8．2ka BP转为为凉干期；6．3～5．4ka BP变为暖湿期；在5．4～4．5ka BP变为温暖、干旱期。由此可以看出，该区古气候演变除有仟年级的变化周期外，还可能存在有百年的气候期。自晚更新世晚期以来台错古湖随着古气候的演变，经历了缓慢扩张，湖水变深，而后又缓慢萎缩，湖水变浅，直至强烈的持续干旱，导致湖泊水位的聚降，使湖泊干枯消失。     

内蒙古克什克腾旗浩来呼热古湖泊全新世以来的环境演变

利用位于中国北方季风尾闾区的浩来呼热古湖泊沉积物中的硅藻化石重建了全新世以来的环境演变历史。根据硅藻组合的变化,可将浩来呼热古湖泊全新世以来的环境演变过程划分为6个阶段:阶段Ⅰ(12.1～11.5cal ka BP),气候以寒冷为主;阶段Ⅱ(11.5～8.6cal ka BP),温度有所回升,但存在一定的冷暖波动;阶段Ⅲ(8.6～6.7cal ka BP),气候仍相对偏凉,且比较干燥;阶段Ⅳ(6.7～5.8cal ka BP),气候开始转温;阶段Ⅴ(5.8～2.9cal ka BP),气候温暖偏湿,为全新世气候最适宜期;阶段Ⅵ(2.9～0.2cal ka BP),气候趋于凉干,湖水也越来越浅,最终在0.2cal ka BP前后干涸消失。     

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。     

Sedimentary Records and the late Pleistocene-Holocene climatic changes in Tai Co,Tibet (Xizang)

西藏西部台错湖T1阶地的两个剖面沉积中,除下部10余厘米含炭化植物和50～70 cm处为暗色碳酸盐粘土及粘土外,中、上部全系粘土碳酸盐层,含丰富的介形类和轮藻类.据碳酸盐、介形类、轮藻类的碳、氧稳定同位素值与微体古生物群落生态特征等提供的环境气候变化指标,指示该区距今41.4～4.5 ka BP间气候变化为:在41.4～26.2 ka BP气候较湿润;26.2～25.5 ka BP偏暖稍干;25.5～22.5 ka BP气候暖湿;22.5～21.0 ka BP气候偏冷湿;20.5～17.5 ka BP气候骤冷、偏湿,反映本区处于末次冰期盛冰期;17.5～16.0 kaBP偏冷偏干;16.0～11.8 ka BP气候偏暖湿,为全球间歇性暖事件的响应;11.8～10.4 ka BP气候较冷干,大致相当于新仙女木期,10.4 ka BP气温开始回升;10.4～9.4 ka BP气候偏暖湿;9.4～8.5 ka BP气候呈现短暂暖湿颤动;8.5～7.9 ka BP气候偏干冷,为冰后期强烈降温偏干事件;7.8～6.3 ka BP气候偏暖湿;6.3～4.5 ka BP气候趋向冷干,4.5 ka BP记录了晚更新世晚期以来最大的干燥期.     

西藏定结盆地中更新世介形类与环境气候变化

西藏定结盆地叶如藏布东岸剖面为一套灰—灰白色粘土质砂、粉砂、细砂与粗砂层所组成的湖相沉积地层,厚约41.3m,该套地层中产丰富的介形类化石,含10属26种,ESR测年数据显示地层沉积时间介于543.8~184.0 kaBP的中更新世时期。本文首次报道了该盆地中更新世时期(543.8~184.0 kaBP)的介形类,据介形类属种类型与丰度值变化,自下而上可分为6个化石组合;结合ESR测年结果,讨论了定结古湖近360 ka的沉积环境与气候变化:543.8~437.9 kaBP,湖区气候偏凉湿,降水较多,湖面较宽,水体较深,但水温不高,水质为微咸水;437.9~347.7 kaBP,湖区气候较上一时期变得寒冷,水体变小,湖水向咸化发展;347.7~264.2 kaBP,气候较上一时期变得更冷,湖泊水体扩大,湖水含盐度减少,向淡化方向发展;264.2~254.9 kaBP,湖区气候更加寒冷,水体温度变得更冷,湖泊水体先缩小后逐渐增大;254.9~239.0 kaBP,湖泊水体减少,湖区气候较前一阶段变暖;239.0~184.0 kaBP,湖水较上一时期有所扩大,淡化明显,湖泊周边环境依然比较寒冷。     

渤海湾西北岸中更新世中期以来的气候环境和沉积环境演变

渤海湾西北岸是渤海湾沿岸砂坝-澙湖沉积体系组成部分,其沉积物蕴含着丰富的地质环境演变信息,是认识该地区气候环境和新构造活动的关键.通过对渤海湾西北岸QEJ01孔80 m以上地层沉积环境、孢粉分析及微体古生物研究,结合测年数据,根据定量古气候重建数据,探讨了本区中更新世中期以来特征时期的植被演替及环境演变,并对MIS6～MIS1各阶段渤海湾西北岸的气候及环境变化进行了区域对比.QEJ01孔450.40～377.14 ka,植被类型以针阔混交林为主,气候温暖干燥,沉积环境由河床逐渐演变为滨海湖泊;377.14～113.96 ka,气候相对寒凉湿润,植被类型以针阔叶混交林-草原为主,沉积环境以湖泊为主,后期为洪泛平原;113.96～98.84 ka,该时期气候波动频繁,以稀树荒漠草原为主,气候温凉湿润,河床发育;98.84～74.33 ka,气候温暖湿润,植被景观为针阔混交林-草原,降水量增加,沉积环境以漫滩湖泊和河床相为主;74.33～48.09 ka,气候异常寒冷干旱,以针叶林为主的稀疏-荒漠草原较发育;48.09～25.72 ka,植被类型为针阔混交林-草原,气候温暖偏湿;25.72～22.52 ka,气候寒凉干旱,植被为稀树-荒漠草原;22.52～3.87 ka,植被类型由常绿落叶阔叶林演变为针阔混交林-草原,气候温暖湿润,沉积环境以三角洲平原为主;3.87～0.0 ka,气候凉爽干旱,植被类型以针阔混交林为主.渤海湾西北岸平原为构造活动的活跃地带,自MIS5阶段以来,沉降中心呈现自北西向南东迁移,以及海侵层的发育程度,均受区域构造运动和气候环境变化的影响控制.     

湖泊记录揭示的中更新世以来我国区域环境分异与亚洲季风的关系

长尺度的湖泊记录的对比研究,可以避免局部的环境因素的干扰,能较好地辨析出大区域乃至全球气候变化的特点。我国目前可供较长时间尺度对比研究的湖泊沉积记录只有青藏高原北部柴达木、云贵高原滇池和青藏高原东部若尔盖古湖,本文根据若尔盖盆地RM孔、柴达木盆地ZK-336及CK-6孔和滇池盆地参1井等钻孔的湖泊深钻记录比较研究,探讨了中更新世以来我国环境的区域分异特点。结果表明:中更新世早期(780～480ka B.P.),青藏高原东部的若尔盖与北部的柴达木地区均以相对湿润的环境为主,但云贵高原似乎表现为暖干的气候特点;中更新世晚期(480～160 ka B.P.),柴达木盆地和若尔盖地区一样,均表现出明显的趋冷趋干的气候特点,柴达木盆地湖泊为一明显的退缩时期,而云贵高原,与青藏高原相一致的是气候的变冷,并且越到后期,寒冷程度加剧,不一致的是该区明显趋湿;晚更新世以来(160～0 ka B.P.),柴达木盆地与若尔盖古湖两者湖泊记录的气侯波动基本一致,但柴达木盆地基本表现为干旱的背景,波动的幅度似乎也不及若尔盖盆地,这可能在于后者处于季风气候的边缘,对气候变化的响应尤为敏感,而位于云贵高原的滇池盆地,和若尔盖地区也     

江汉平原沔城M1孔的沉积特征与古环境重建

通过对江汉平原沔城M₁孔湖泊沉积物进行沉积特征、粒度、14C年代、孢粉分析,重建了晚冰期以来该地区古环境、古气候演化的过程和序列:晚冰期后期有一扩张期,气候温湿并出现湖泊相沉积;晚冰期末期气候温凉偏干、河流环境;全新世初期(10-8.9kaBP),气候转向温湿;全新世大暖期(8.9-3.5kaBP),总体上气候温暖湿润,其中6.8-4.9kaBP是最宜期,4.9-4.8kaBP和4.4-4.2kaBP为两次降温事件,4.8kaBP积水湖盆开始形成,3.9-3.5kaBP为云梦泽鼎盛期;全新世晚期(3.5-1.7kaBP),气温较大暖期有所下降,其中3.5-2.5kaBP温凉偏湿,2.5-1.7kaBP较为温湿,湖泊较为稳定,1.7kaBP开始,云梦泽萎缩,钻孔所在位置出露水面。      

西藏色林错12ka以来的湖泊退缩过程——基于古湖岸线的OSL测年

青藏高原内陆封闭湖泊的水体演化是古气候变化的良好地质载体,其中湖泊古湖岸线变迁蕴含了丰富的地质信息,对其识别和研究是认识导致湖泊退缩的气候或构造变化的关键。色林错是青藏高原第二大内陆湖泊,保存了一系列古湖岸线。我们对色林错东北岸保存完好的古湖岸线进行了研究。对这些古湖岸线样品中的石英颗粒使用单片再生法(Singlealiquot regeneration)进行OSL测年,测定年龄分别为12.2±0.8 ka、6.3±0.4 ka和2.3±0.2 ka。表明色林错在约12.2 ka、6.3 ka和2.3 ka±至少出现了3次阶段性湖泊收缩过程。     

西藏台错盐湖TT-1剖面的沉积特征和年代学研究

台错位于西藏羌塘高原西部,这里因环境恶劣而无人类污染和影响。笔者调查了该湖区一级阶地的湖相化学沉积,取得了TT-1剖面(厚度369cm)连续样品156个,平均单样厚度2．36cm。就台错剖面的年代测定,本文分别对同一样品进行了不同方法的测试和相互校验。研究表明,^14C方法对有机物质的定年是准确的,而在消除盐湖化学沉积建造中碳酸盐的“新碳”、“老碳”的影响方面,仍需做进一步的研究。与此同时,铀系法测年的全溶样品的等时线技术,避免了同位素的分馏问题,所有的测试数据在等时线上都有良好的线形关系,表明获得的年龄数据是合理的。从而确定了TT-1剖面盐湖沉积的可靠地质时代为32．6～4．5ka B P间的晚更新世晚期至全新世中期。     

Evidence of Abrupt Climate Change during the Mid- to Late- Holocene Recorded in a Tropical Lake, Southern China

Research on abrupt paleoclimatic and paleoenvironmental change provides a scientific basis for evaluating future climate. Because of spatial variability in monsoonal rainfall, our knowledge about climate change during the mid-to lateHolocene in southern China is still limited. We present a multi-proxy record of paleoclimatic change in a crater lake, Lake Shuangchi. Based on the age-depth model from 210 Pb, 137 Cs and AMS14 C data, high-resolution mid-to late-Holocene climatic and environmental records were reconstructed using multiple indices(TOC, TN, C/N, δ13 C and grain size). Shuangchi underwent a marked change from a peat bog to a lake around 1.4 kaBP. The C3 plants likely dominated during 7.0–5.9 ka and 2.5–1.4 kaBP, while C4 plants dominated between 5.9–3.2 and 3.0–2.5 kaBP. Algae were dominant sources of organic matter in the lake sediments after 1.4 kaBP. Several intervals with high concentrations of coarser grain sizes might be due to flood events. These results reveal that several abrupt paleoclimatic events occurred around 6.6 ka, 6.1 ka, 5.9 ka, 3.0 ka, 2.5 ka and 1.4 kaBP. The paleoclimatic change recorded in the lake may be related to the migration of the Intertropical Convergence Zone(ITCZ) and El Ni?o-Southern Oscillation(ENSO) activity.     

Sedimentation Geochemistry and Environmental Changes during the Late Pleistocene of Paleolake Qarhan in the Qaidam Basin

On the basis of the analyses of TOC, CaCO3, δ13Corg, δ18O, and δ13C of the shell bar section in the Qaidam basin, and compared with grain size data, the environmental change history of the high water level of paleolake Qarhan was reconstructed and it could be divided into five stages. From 39.7 to 35.8 kaBP was the development period of high paleolake level. From 35.8 to 33.6 kaBP and 33.6 to 27.2 kaBP, TOC and CaCO3 contents and δ18O values were high, whereas, δ13Corg values and median size content were low, reflecting a warm-humid climate and high lake level. During 27.2-22.3 kaBP and 22.3-17.5 kaBP, both temperature and the lake level were lower than those in the previous stages, but the climate was still warmer and more humid than that of today. The lake level decreased between 32.4 and 32.2 kaBP, 30.4 and 29.8 kaBP, and 28.4 and 27.2 kaBP. Generally, the climate was warm and humid in Qaidam basin and the high lake level sustained between 39.7 and 17.5 kaBP. The lake retreated abruptly at 17.5 kaBP, with a very strong increase in evaporation, which resulted in salt formation and the extinction of Corbicula.     

太湖14000年以来古环境演变的湖泊记录

本文根据东西太湖短柱岩芯的沉积物的物理、化学、生物指标的综合分析,讨论了该区距今14ka来的古气候变化过程,结果表明14.3-13.3kaBP,太湖水位低,环境指标甚至表现为暴露特征,反映了气候干旱:13.3-12.4kaBP,为偏暖湿的过渡阶段;该孔柱270-280cm (11.5kaBP左右)各类指标均明显反映冷干特征,可能是YoungerDrays事件的记录,与我国东部其它地区有可比性;约10.9-10kaBP,这一时期是整个研究时段内一个较显著的温暖期。表现为还原沉积环境和水位相对较深;约10-7.2kaBP为冷暖交替的过渡带;7.2-5.737kaBP为暖湿气候;5.05kaBP多项分析指标发生突变,反映物源发生显著变化,可能存在沉积间断;表层沉积物则呈现现代环境的特征,西太湖藻类生长茂盛,偏氧化的沉积环境。目前湖泊生产力较高,富营养化程度高,表现为藻型湖泊特征;东太湖有机质来源以东太湖中生长较为茂盛的维管水生植物为主,目前湖泊生产力较低,富营养化程度低,表现为典型的草型湖泊特征。      

Holocene Vegetation and Climate Changes in the Huangqihai Lake Region, Inner Mongolia

A consensus on Holocene climate variability at the modern northern fringe of the East Asian summer monsoon (EASM) region remains elusive. Here, we present a pollen-based reconstruction of vegetation history and associated climate variations of a sediment core from Huangqihai Lake, central Inner Mongolia. During 10.7 to 8.8 cal kaBP, typical steppe with small patches of forest dominated the lake area, suggesting a moderately wet climate, followed by ameliorating climatic conditions until 8.0 cal kaBP as deduced by the expansion of forest. Typical steppe recovered the lake area between 8.0 and 7.2 cal kaBP, reflecting a deterioration of climatic conditions; in combination with other proxy records in the study region, we noticed that severe aridity was prevailed in the lake area between 8.0 and 7.6 cal kaBP. During 7.2 to 3.2 cal kaBP, abundant tree pollen indicated dominance of forest-steppe around the lake, marking regionally wet conditions. A notable absence of broadleaved trees after 5.2 cal kaBP reveals a slight drying trend, and climate deterioration from 4.5 to 4.1 cal kaBP might be linked to the 4.2 ka event. After 3.2 cal kaBP, a transition to steppe was associated with dry conditions in the region. Based on our pollen record and prior paleoclimatic reconstructions in the Huangqihai Lake region, there was a generally-accepted, stepwise shift to a wet climate during the early Holocene, an overall humid climate from 7.2 to 3.2 cal kaBP, and then severe drought for the rest of the Holocene. Moreover, regional comparisons among pollen records derived from lakes situated in the temperate steppe region suggested a roughly synchronous pattern of vegetation and climate changes during the Holocene and demonstrated an intensified EASM during the middle Holocene.     

Climate Reconstruction based on Pollen Analysis in Inner Mongolia, North China from 51.9 to 30.6 kaBP

The palynomorph assemblage of lake sediments younger than 51.9 kaBP from Wulagai Gobi in Inner Mongolia was analyzed to reconstruct the vegetation and climate.From 51.9 to 30.6kaBP,the vegetation was arid to semi-arid grassland with only slight changes.According to the palynomorphs,trees and shrubs were very rare.The large number and diversity of algae indicate the presence of a lake.Quantitative climatic conditions were reconstructed using the Best Analogues Method.The results indicate that the annual mean temperature was higher than that at present.The combination of temperature and annual precipitation suggests a change in the climate from cool dry to warm dry and then cool humid.Our results show that the annual precipitation values were mostly higher than that at present but were lower than 400 mm.It infers that the study area was already within the arid to semi-arid regions but with a stronger influence of the summer monsoon during 51.9to 30.6 kaBP than at present.With slight differences mainly in time scale,the changing trend of the annual temperature curve is consistent with the other climatic records from Antarctica,Greenland,Hulu Cave(East China),and the Tibetan Plateau during the last glacial period.From 30.6 kaBP to present,very few palynomorphs were detected in the samples.Hence,no information about the vegetation and climate could be extracted.Combined with other studies during Late Pleistocene,we presume that the reason for the lack of pollen during this period was caused by an abrupt temperature fall after 30.6 kaBP or that the lacustrine conditions were unsuitable for pollen deposition.It was probably incurred by the oxidation on land prior to deposition.But for those samples only with algae,it might be caused by the fact that algae could finish their life history in a very short time in a seasonal lake.     

柴达木察尔汗贝壳堤剖面Sr同位素及其环境意义

根据对柴达木盆地察尔汗古湖贝壳堤剖面酸不溶组分和酸溶组分的提取及其87Sr/86Sr的测定,结合沉积物中Rb/Sr的变化,指出Sr同位素组成特征可有效指示源区化学风化和沉积区古环境变化;依据酸溶组分中盐度指标Sr/Ca, Sr/Ba值与Sr同位素组成曲线的对比分析,揭示酸溶组分Sr同位素可以较好的指示水体形成时的盐度。通过分析贝壳堤剖面化学风化和部分盐度变化过程,探讨了研究区晚更新世39.6~ 17.1 ka BP(未经校正的AMS 14C测年结果,全文同)湖泊高湖面的演化历史。     

北京延庆古湖正构烷烃分布特征及古气候意义

为了更好地了解华北平原核心区延庆盆地古气候演化,利用气相色谱仪对北京延庆盆地阜高营剖面湖相沉积物中的正构烷烃进行了检测.结果表明其正构烷烃含量丰富且连续,碳数分布范围为C₁₆~C₃₃,高碳数奇碳优势明显,中链和短链烷烃均无奇偶优势,多以C₂₉或C₃₁为主峰的单峰分布为主,同时存在少量低碳数和高碳数并存的双峰型.延庆古湖有机质以陆生植物为主,包含少量的菌藻类和水生植物.综合ESR年代序列、有机碳同位素（δ13C_org）、长链正构烷烃平均链长（average chain length,ACL）碳优势指数（carbon preference index,CPI）和正构烷烃Paq参数,将延庆盆地晚更新世中期以来的环境演变划分为:56.8~45.6 ka,气候暖湿,湖泊发育良好,湖面较高;45.6~31.5 ka,气候温湿,湖泊发育缓慢,水位略有下降;31.5~20.0 ka,气候冷干,湖泊水位严重下降;20.0~13.4 ka,气候较为干冷,有转暖趋势;13.4~9.2 ka,气候转暖,湖泊有所发育,但水位较低;9.2 ka至今,气候变干,湖泊萎缩.延庆古湖沉积物中正构烷烃参数的变化与古里雅冰心、李家塬黄土、深海氧同位素反映的气候变化较为一致,呈现冰期-间冰期旋回,且受控于同纬度太阳辐射量的变化.      

末次冰期间冰阶(40～22kaBP)内蒙古黄旗海古降水量研究

末次冰期间冰阶(40～22kaBP),黄旗海最高古湖面稳定在1310～1318m之间,比现代湖面约高50m,湖泊面积达到450～515km2(平均为466km2),是现代湖面101km2(1950～1961年平均值)的4.4～5.1倍,湖泊补给系数7.8～9.1。利用逐次逼近法寻找古流域的现代气候相似区域,从而确定相关参数定量重建古降水量;在此基础上,附加另外两个过程,检验了重建结果的可靠性。重建结果认为:40～22kaBP古湖面稳定存在时,黄旗海流域的古降水量可达479～497mm/a,比现在年平均值(353mm/a)高约126～144mm/a。