北京延庆古湖沉积物粒度敏感组分记录的区域冬季风演化历史

采用标准偏差方法提取了延庆盆地阜高营剖面湖相沉积物的敏感粒度组分,得出粗粒敏感组分2(26~159μm)能有效指示冬季风的强弱。根据经验正交函数(EOF)对其整体粒度进行了分解,其中EOF1组分(22μm)的贡献率高达53.8%,指示降水量的多少。研究显示,粗粒敏感组分2与EOF1组分比值的变化可以作为研究区冬季风强弱和干旱化的指标,粗粒敏感组分2增加,EOF1组分减少,表明冬季风加强,气候变干,湖泊发育受限。研究区冬季风演化过程表现出冰期-间冰期旋回特征:56.8~45.6ka冬季风弱,降水量大,湖面较高;45.6~31.5ka冬季风开始加强,降水量减少,水位略有下降;31.5~13.4ka冬季风强盛,降水量较少,湖泊趋于萎缩;13.4ka至今冬季风微弱,降水适中,湖泊发育缓慢。     

湖泊沉积物中风成和水成组分定量判据的初步研究———以青海湖为例

对青海湖沉积物进行物质来源进行聚类分析, 并对周边风成黄土与现代湖泊表层沉积物进行粒度分析, 在此基础上, 以青海湖周边典型风成黄土作为风成组分端元, 以青海湖表层沉积物作为水成组分端元, 首次利用已知端元的粒度分布特征对青海湖沉积物中典型粒度分布进行拟合, 进而估算了其中风成和水成组分的比例。结果表明, 青海湖沉积物粒度分布特征可分为三大类:1.水成组分占主导; 2.风成组分占主导(风成黄土主导); 3.两者以不同比例混合。希望此方法能成为未来湖泊沉积物中不同组分的定量判据和古环境的解读提供新途径。      

天津滨海平原区深孔沉积物环境敏感粒度提取及其意义

沉积物环境敏感粒度是进行古环境研究的重要方法之一, 然而华北平原地区很少进行完整的第四纪全取心深孔沉积物环境敏感粒度组分的提取及分析.对天津渤海湾G1和G2孔第四纪沉积物样品进行粒度分析, 采用粒级-标准偏差和主成分分析两种方法进行了沉积物环境敏感粒度组分提取.对比提取结果发现, 两种方法存在差异性的同时还存在一定的兼容性, 沉积层理厚度越薄, 兼容性越明显; 主成分分析方法对沉积物环境敏感粒度组分刻画得更为细致, 粒级-标准偏差方法不适合深孔沉积物整体敏感粒度组分的提取.G1孔环境敏感粒度组分的粒度峰值为6.700μm、15.650μm、36.240μm、176.900μm、282.100μm、716.800μm; G2孔环境敏感粒度组分的粒度峰值为0.578μm、176.000μm, 分别对应6个和3个粒度分布区间, 指示两孔整体上的沉积物来源及沉积环境空间存在差别.G2孔相对于G1孔整体上的沉积强度大且沉积环境较为稳定, 适合于开展高分辨率的古环境重建工作.      

江陵剖面沉积物的粒度特征及其古气候意义

通过对江汉平原江陵剖面高分辨率采样，利用激光粒度仪对沉积物粒度进行测试，分析了粒度的组成及其参数特征，结合孢粉资料和岩性特征，探讨了粒度在该区的古气候意义。结果表明，降水量较大的湿润气候条件下沉积物的粗颗粒组分明显增多；而降水量相对较少的干旱气候条件下沉积物的粗颗粒组分相对减少。通过与邻区对比．江汉平原江陵剖面沉积物粒度所揭示的该区近9000aB．P．以来的古气候变化与国内相邻区域其他指标的研究结果相一致。     

中国北方部分地区黄土、沙漠沙、湖泊、河流细粒沉积物粒度多组分分布特征研究

通过对我国北方部分地区的黄土、沙漠沙、湖泊、河流细粒沉积物的粒度多组分分布特征系统研究后总结了其粒度分布特征及组分间差异,并提出了风成、水成沉积物成因类型的判别依据。认为:1)细粒沉积物粒度一般由多个组分叠加构成,表现为多组分粒度分布特征。2)黄土粉尘粒径以<70 μm的悬浮颗粒为主,粒度由粗、中、细三个组分构成。粗粒组分含量最高,其中值粒径与源区距离呈负相关,中粒组分百分含量与源区距离呈正相关。3)沙漠沙粒度由一个极其明显的粗粒跳跃组分构成,中值粒径一般位于100~300 μm,分选性极好。4)湖泊沉积物粒度分布最多可有6个组分(中值粒径:<1 μm,2~10 μm,10~70 μm,70~150 μm,150~700 μm,>700 μm),前4个组分属悬浮组分,⑤为跳跃组分,⑥为滚动组分,分选性差。5)河流沉积物粒度分布曲线较复杂,其分布特征蕴含了水动力强弱信息。6)沙漠沙→黄土与河流沙→湖泊沉积物其优势组分的粒径均逐渐变细,但水成相对应组分比风成组分粒径要粗.     

长江武汉段天兴洲低滩沉积物粒度端元对河流—风成沙丘沉积环境的指示意义

河床沙波向风成沙丘演变的过程具有特殊的沉积动力机制。笔者等以68份长江武汉段天兴洲洲头低滩沉积物的粒度分布数据为例,利用端元分析方法从每个粒度分布中分离提取4个粒度端元组分(EM1、EM2、EM3和EM4),探讨了河流—风成沙丘不同沉积环境中粒度端元的异同。研究结果表明：EM1和EM3组分在粒度分布中占比与沉积物粒度中值分别呈较好的线性正相关和负相关;河流沉积物主要由EM1、EM2和EM3组成的跳跃方式搬运,对应滚动次总体的EM4组分占比5%～10%,少悬浮搬运;风成沙纹沉积物主要包括两段跳跃次总体,以EM2组分为主、EM1和EM3组分为辅,少EM4组分;沙丘背风面沉积物主要靠颗粒流顺坡滑塌,以EM2组分为主、EM1和EM3组分为辅,含占比约为5%的EM4组分;未被风成沙纹覆盖的沙丘波谷沉积物记录了河流和小型滞水洼地的沉积特征,代表滚动次总体的EM4组分占比7%～15%,悬浮次总体占比可达20%。本文提取的沉积物粒度端元为弱风环境中河道内局部小型河流—风成沙丘的沉积环境和演化过程研究提供了参考。     

长江武汉段天兴洲低滩沉积物粒度端元对河流—风成沙丘沉积环境的指示意义

河床沙波向风成沙丘演变的过程具有特殊的沉积动力机制。笔者等以68份长江武汉段天兴洲洲头低滩沉积物的粒度分布数据为例,利用端元分析方法从每个粒度分布中分离提取4个粒度端元组分(EM1、EM2、EM3和EM4),探讨了河流—风成沙丘不同沉积环境中粒度端元的异同。研究结果表明：EM1和EM3组分在粒度分布中占比与沉积物粒度中值分别呈较好的线性正相关和负相关;河流沉积物主要由EM1、EM2和EM3组成的跳跃方式搬运,对应滚动次总体的EM4组分占比5%~10%,少悬浮搬运;风成沙纹沉积物主要包括两段跳跃次总体,以EM2组分为主、EM1和EM3组分为辅,少EM4组分;沙丘背风面沉积物主要靠颗粒流顺坡滑塌,以EM2组分为主、EM1和EM3组分为辅,含占比约为5%的EM4组分;未被风成沙纹覆盖的沙丘波谷沉积物记录了河流和小型滞水洼地的沉积特征,代表滚动次总体的EM4组分占比7%~15%,悬浮次总体占比可达20%。本文提取的沉积物粒度端元为弱风环境中河道内局部小型河流—风成沙丘的沉积环境和演化过程研究提供了参考。     

渤海湾西部表层沉积物粒度特征与沉积混合

根据渤海湾西部135个表层沉积物样品的粒度分析结果,分析了表层沉积物的粒度特征与规律。整体上由研究区东北部沿海岸向南沉积物粒度变细,由砂和粉砂质砂变为砂质粉砂,再变为粘土质粉砂。沉积物粒度频率曲线显示,由研究区东北部至北部,沉积物粗组分含量减少,由单峰逐渐过渡为主峰或弱峰,到中部粗组分减少为粗尾形态,到南部粗组分几乎缺失;而沉积物细组分的变化趋势则与之相反。沉积物粗组分在粒度频率曲线上的表现由单峰逐渐过渡至主峰或次峰,粗峰含量减少,到中部粗组分减少为粗尾形态,到南部粗组分几乎消失;而沉积物细组分的变化趋势则与之相反。沉积物粒度参数的平面分布规律和粒度参数之间的相关性变化形态显示出粗细2种母质组分以不同比例的沉积混合的特征,即来自东北部的粗组分与来自南部的细组分发生混合,这可能主要与区内双向的沿岸环流输运有关。     

湖泊沉积物粒度分析方法在古气候环境研究中的应用

沉积物的粒度是衡量沉积介质能量和沉积盆地能量的一种重要代用指标,与沉积环境的关系非常密切,在古气候古环境研究中,湖泊沉积物的粒度指标发挥着重要的作用。刘兴起等人利用全样粒度分析方法对青海湖QH-2000钻孔的沉积物粒度特征进行了详细研究,结果表明冷干和暖湿气候条件下沉积物的粗颗粒组分增多,介于二者之间的气候条件下,沉积物的粒径变化相对比较平缓。Xiao Jule等利用正态函数分布拟合法,将Dali湖沉积岩心的粒度组分划分为6种,通过对各组分峰值粒径等粒度参数的分析研究,得出各组分含量及其峰值粒径等的变化与湖泊水位关系密切。根据建立起的湖泊沉积物粒度参数与气候环境之间的耦合关系,最后将达里湖1.2kaBP以来的水位波动划分为不同的5个阶段。     

额济纳盆地GN100钻孔不同沉积相的粒度特征

内蒙额济纳盆地GN100钻孔的沉积相可划分为河流相、湖泊相、沼泽相及风成砂沉积。对该钻孔不同沉积相代表性 沉积物的粒度分析表明：额济纳盆地沉积物的粒度特征能够有效区分沉积环境和动力过程。河流相沉积物主要粒度组分为 粗砂,以滚动搬运为主,判别值Y为大于1;风成砂主要粒度组分为细砂,Y值范围主要在0附近;沼泽相也以细砂为主且 较风成砂更细,Y值主要为负值且小于风成砂;湖相粒度组分主要为细粉砂,以悬浮搬运为主,但不完全是静水悬浮搬 运,相比于静水沉积相对颗粒偏大,而Y最小,为小于-9。这些结果可以为区域沉积环境的准确解释提供参考。     

A Holocene dust record in arid central Asia inferred from Lake Barkol,northwest China

Grain-size distributions and detrital minerals were investigated for modern dust and for lacustrine sediment in Lake Barkol region, northwest China. Characteristics of the modern dust and lacustrine sediments, principle component analysis, and changes of quartz contents all suggest grain size 45–138 μm in the core sediment is the dust sensitive component. It indicates that high dust flux climate occurred at mid-Holocene (5.5–4.5 cal ka BP), corresponding to the high dust flux record in northwest Pacific and the drought interval of deserts in northwest China during the mid-Holocene. The strong dust activity is in contradiction with the climatic optimum recorded by the lacustrine evidence in Xinjiang. Different responses of the dust source region and watershed to the regional climate may have led to the inconsistency between dust and climate records during the mid-Holocene in arid central Asia.     

干旱区湖泊沉积物粒度组分记录的区域沙尘活动历史: 以新疆巴里坤湖为例

根据中国西北干旱区巴里坤湖BLK 1剖面沉积物的粒度分析,采用粒级—标准偏差法提取了对沉积环境变化敏感的粒度组分。结果表明,巴里坤湖沉积物中45～170 μm粒级组分含量和平均粒径对研究区区域性风沙活动较为敏感,据此结合14C测年数据重建了研究区9400 cal aBP以来的风沙活动历史。在过去的2 000年内,巴里坤湖地区尘暴事件多发或强风沙活动时段主要出现在240～440 cal aBP、600～1 280 cal aBP和1 400～1 800 cal aBP期间,这些时段同历史时期的雨土频率高值期、古里雅冰芯阴阳离子高含量期较为一致。从更长地质时期来看,8 000～8 300 cal aBP、7 400～7 700 cal aBP、6 500～7 000 cal aBP时段,特别是在中全新世(3 900～6 100 cal aBP)期间,区域性的尘暴事件或强风沙活动尤其频繁,这些时段同古里雅冰芯中微粒浓度、敦德冰芯中的微粒含量记录均可以进行良好的对比。干旱区封闭湖泊沉积是记录地质历史时期风沙活动的良好载体,但由于气候环境变化往往具有较强的区域性特征,因此,对某一剖面沉积物环境敏感粒度组分的提取及应用不具有普适性。     

末次盛冰期以来中国北方干旱区演化及短尺度干旱事件

对中国北方干旱区329个古土壤和湖泊沉积物的14C年龄数据的时空分布及频数统计分析表明, 从末次盛冰期至冰消期, 我国整个干旱区受控于西风带;在全新世, 干旱区东部环境变化主要受控于东亚季风系统, 而其西部仍属西风控制区。全新世以来, 中国干旱区存在至少4次百年至千年级的干旱事件, 且干湿变化基本上与全球西风模式区的气候变化相反, 而与低纬非洲干旱区气候变化有很好的对应关系 。由于我国干旱区和非洲干旱区的干湿变化均受控于来自低纬热带海洋的夏季风的强弱, 因此　两区干旱事件的同时发生可能与低纬热带海洋的气候变化有关。同时, 本文利用14C年龄的时空分布和其它地质资料, 初步恢复了末次盛冰期和全新世最适宜期我国干旱区的沙漠分布状况。     

新疆巴里坤湖全新世环境记录及区域对比研究

选择位于西风环流显著影响区的巴里坤湖作为研究对象,采用¹⁴C测年建立了巴里坤湖沉积剖面约9400cal.aB.P.以来的时间序列。对该湖泊剖面沉积物的矿物X射线衍射、自生碳酸盐稳定同位素、碳酸盐含量和粒度指标的综合分析表明,9400cal.aB.P.以来,巴里坤湖地区的气候环境变化大致经历了冷干（9400～7400cal.aB.P.）-暖湿（7400～5900cal.aB.P.）-暖干（5900～3100cal.aB.P.）-凉湿（3100～1100cal.aB.P.）-冷干（1100～500cal.aB.P.）-暖干（500cal.aB.P.以来）的气候变化过程,该过程基本上同周边区域的气候环境变化记录相一致。在3800cal.aB.P.左右,北疆地区的几个典型湖泊沉积记录序列都指示该时期气候环境发生了较为明显的转折,可能暗示了这一时期亚洲中部干旱区（至少在北疆地区）大气环流状况发生了重大调整。     

A Holocene climatic record denoted by geochemical indicators from Barkol Lake in the northeastern Xinjiang,NW China

The Barkol Lake, as a closed inland lake, is located at the northeast Xinjiang in northwest China. A combination of geochemical indicators including δ¹⁸O and δ¹³C of carbonate, TOC, carbonate contents, as well as grain size proxies and magnetic susceptibility of sediments obtained from a newly recovered section at this lake, provides a high-resolution history of climatic change in the past 9400 years. Multi-indicators reflect that Holocene climatic change in the study region generally follows the Westerly Wind pattern of Holocene, and three climatic periods can be identified. Between 9400 and 7500 cal a B.P., climate was characterized by relatively drier and colder condition. From 7500 to 5800 cal a B.P., a relatively warmer and moister climate prevailed, but between 5800 and 3500 cal a B.P., climate shifted towards warmer and drier conditions. A relatively colder and wetter climate prevailed during 3500∼1000 cal a B.P., then it changed towards cold and dry between 1000 and 500 cal a B.P.; after 500 cal a B.P., climate changed towards warm and dry conditions again. This study reflects that during the Middle Holocene (from ca 7000 to 3500 cal a B.P.), variations of carbonate δ¹⁸O of sediments from several lakes in the northern Xinjiang were synchronous with that of Qinghai Lake, where was strongly influenced by the South Asian monsoon; however, after 3500 cal a B.P. this consistency was interrupted, possibly resulting from a re-domination of the Westerly Wind and the retreat of South Asian monsoon in the northern Xinjiang.     

全新世以来巴里坤湖面积变化及气候环境记录

通过新疆北天山东段巴里坤山北麓巴里坤湖及周缘地区7个剖面的沉积相带划分、OSL测年、粒度分析、磁化率测试,研究了全新世以来巴里坤湖区湖面积变化:14 000 a B.P.末次冰盛期晚期,东天山地区冰川发育,由于水体封存于巴里坤山冰川,导致巴里坤湖萎缩至1#剖面以北。8 000～4 000 a B.P.巴里坤山冰川融化,巴里坤湖扩张进入全新世以来最大湖期,湖泊扩张至1#剖面以南,面积达到600 km2。东天山地区温暖湿润的全新世适宜期为8 000～4 000 a B.P.。其后湖泊逐渐萎缩,4 000～2 000 a B.P.湖泊面积大约470 km2。2 000～1 000 a B.P.面积萎缩至380 km2。在1 500 a B.P.左右湖泊曾经基本干涸,在目前湖心地带出现泥坪沉积。其后巴里坤湖进入小湖期,湖泊面积在100 km2范围波动,时有扩张或干涸。全新世巴里坤湖水位变化主要受北半球夏季太阳辐射变化控制,具体表现在北半球冰盖由扩张转为融化背景下,全新世早期巴里坤山冰川发育和全新世中期的巴里坤湖冰川融水的注入扩张;巴里坤地区受东亚夏季风影响甚弱,西风环流带给的水量补充有限,全新世中晚期巴里坤地区向干旱环境发展。     

Mid-Holocene climate change in the eastern Xinjiang region indicated by the grain size and stable isotope record from Lake Barkol, northwest China

A sediment core from Lake Barkol located in the eastern Xinjiang autonomous region, northwest China, provided a high-resolution record of environmental change covering the last ~8.6 cal ka BP. Three major climate stages, 8.6–7.1, 7.1–2.0 and from 2.0 cal ka BP to the present, were divided by grain size and the authigenic carbonate stable isotope of the lake sediment. Climatic drought during the period 7.1–4.5 cal ka BP, deduced from Lake Barkol, prevailed in the mid-Holocene climate in northern Xinjiang and northwest Mongolia. In contrast, it was wet in central Xinjiang, northwest India and the Middle East during the same period. The climatic difference between northern and southern arid central Asia demonstrates the southward shifting of the Westerlies, which indicates the potential contribution of the Siberian high in the mid-Holocene.     

OSL chronology of sand deposits and climate change of last 18 ka in Gurbantunggut Desert,northwest China

The development of the Gurbantunggut Desert is mainly controlled by the Westerly wind, and at present has little influence from Indian and Southeast Asian monsoons. A combined study using optically stimulated luminescence (OSL) dating, ground‐penetrating radar (GPR) surveys and climatic proxies analysis was carried out in the southern part of the desert. The chronology extends back to 18 ka and is constructed based on 16 OSL ages from boreholes in the linear dune body and the inter‐dune area. The chronology suggests that sand deposition in the last 18 ka experienced two rapid accumulation phases at 11 and 2.5 ka ago which were also evident from the GPR surveys. These periods relate to increased aridity in the region. Five climate phases are identified from the last 18 ka, based on the OSL chronology and climatic proxy analysis with grain size and magnetic susceptibility measurements. The deglacial period (18.3–10.4 ka) is characterized by climate instability and possible glacial melting events. The Holocene Optimum peaked 8.5 ka and terminated 3.6 ka ago, when the regional climate became arid. OSL samples from the dune body cluster around 2.5 ka, which indicates rapid advance/extension of dune bodies at this time. Copyright © 2011 John Wiley & Sons, Ltd.     

Linking moisture and near-surface wind with winter temperature to reveal the Holocene climate evolution in arid Xinjiang region of China

An increasing number of palaeo-climatic records have been reported to identify the Holocene climate history in the arid Xinjiang region of northwest China. However, few studies have fully considered the internal linkages within the regional climate system, which may limit our understanding of the forcing mechanisms of Holocene climate change in this region. Here, we systematically consider three major issues of the moisture/precipitation, temperature and near-surface wind relevant to the Holocene climate history of Xinjiang. First, despite there still has debated for the Holocene moisture evolution in this region, more climatic reconstructions from lake sediments, loess, sand-dunes and peats support a long-term regional wetting trend. Second, temperature records from ice cores, peats and stalagmites demonstrate a long-term winter warming trend during the Holocene in middle- to high-latitudes of Asia. Third, recent studies of aeolian sedimentary sequences reveal that the near-surface winds in winter gradually weakened during the Holocene, whereas the winter mid-latitude Westerlies strengthened in the Tienshan Mountains. Based on this evidence, in the arid Xinjiang region we propose an early to middle Holocene relatively cold and dry interval, with strong near-surface winds; and a warmer, wetter interval with weaker near-surface winds in the middle to late Holocene during winter. Additionally, we develop a conceptual model to explain the pattern of Holocene climate changes in this region. From the early to the late Holocene, the increasing atmospheric CO₂ content and winter insolation, and the shrinking of high-latitude continental ice-sheets, resulted in increasing winter temperatures in middle to high latitudes in the Northern Hemisphere. Subsequently, the increased winter temperature strengthened the winter mid-latitude Westerlies and weakened the Siberian high-pressure system, which caused an increase in winter precipitation and a decrease in near-surface wind strength. This scenario is strongly supported by evidence from geological records, climate simulation results, and modern reanalysis data. Our hypothesis highlights the important contribution of winter temperature in driving the Holocene climatic evolution of the arid Xinjiang region, and it implies that the socio-economic development and water resources security of this region will face serious challenges presented by the increasing winter temperature in the future.     

Holocene palaeoflood events recorded by slackwater deposits along the middle Beiluohe River valley,middle Yellow River basin,China

Palaeohydrological investigations were carried out in the middle Beiluohe River valley in the middle Yellow River basin. Palaeoflood slackwater deposits (SWDs) are natural records of overbank flooding and are often identified in the Holocene aeolian loess–soil profiles along the river valley. Three bedsets of palaeoflood SWDs were found within the mid‐Holocene Climatic Optimum palaeosol (S₀) on the right riverbank. Both the sedimentary and the analytical results, including magnetic susceptibility, grain‐size distribution and concentrations of chemical elements, indicate that these palaeoflood SWDs were deposited from the suspended sediment load of overbank flooding. We identified three episodes of extraordinary overbank flooding events. These hydro‐climatic events were dated to 7600–7400, 5800–5000 and 4200–4000 a BP, from optically stimulated luminescence (OSL) dating and pedostratigraphical correlation. The minimum flood peak discharges were estimated to have been between 12 600 and 14 100 m³ s^?1 using the slope–area method. These hydro‐climatic events are considered to be a regional expression of known climatic events and demonstrate that the mid‐Holocene climate was far from stable. These results show that the magnitudes of floods are highly sensitive to climate change in semi‐arid and sub‐humid regions with a monsoonal climate.