黄河中游吉县段全新世古洪水滞流沉积物光释光测年研究

通过对黄河中游河口镇-龙门段峡谷进行详细的野外考察,在多个地点发现了含有古洪水滞流沉积物的全新世地层剖面。对山西省临汾市吉县段冯家集剖面的古洪水滞流沉积物系统采样,进行了沉积学及年代学分析研究。野外观测和粒度成分分析表明冯家集剖面夹有5层典型的古洪水滞流沉积物,其性质为细沙质粉沙,具有水平层理,层与层之间被坡积石渣土分隔。该层系的顶界高出黄河平水位达18m。它们是特大洪水在高水位滞流情况之下的悬移质沉积物,客观地记录了全新世时期黄河中游一期5次特大古洪水事件。通过分离出125—2251~m石英颗粒,应用单片再生剂量法(sAR)测得其光释光年龄值,结合地层对比及各种气候替代性指标的分析,确定这些古洪水事件发生在3200~3000a B.P.之间,处于全新世中期大暖期向全新世晚期相对干旱期转折的阶段。这对应我国历史上的商末一西周初期,季风气候状态不稳定,黄河流域既有严重地干旱,又有特大洪水事件发生。本文的研究成果为深入揭示河流水文系统对于全球变化的响应规律提供了新的可靠证据。     

汝河全新世古洪水沉积学与光释光测年研究

汝河流域曾发生过堪称世界之最的"1975·8河南驻马店特大洪水垮坝事件",其洪水规模之大,受灾面积之广,受灾及死亡人数之多,震惊世界。因此探究汝河特大洪水事件的发生规律及其气候背景具有极其重要的科学价值。通过对汝河流域开展广泛细致的野外考察,在驻马店-遂平段第一级河流阶地前沿发现多处全新世古洪水滞流沉积物剖面,记录了流域发生的气候水文事件信息。最终选取汝河诸市乡地点(ZSX)全新世黄土土壤剖面进行系统采样,结合沉积学指标研究,准确鉴别出汝河ZSX黄土古土壤剖面中所夹三组古洪水滞流沉积物(slackwater deposits,SWD),为典型河流洪水悬移质泥沙沉积物。结合地球化学特征分析,确认三组古洪水SWD的物质是汝河上游流域发生特大暴雨洪水期间,流域地表土壤侵蚀与水土流失的产物。这三组古洪水滞流沉积物记录了末次冰消期和全新世发生在汝河流域的三期古洪水事件。结合典型剖面地层对比和应用SAR法对剖面关键沉积层位进行光释光测年(optical stimulated luminescence dating,OSL),建立了准确的地层年代框架。这三期古洪水事件分别发生在12000~11200aBP、4200~4000aBP、3200~3000aBP,皆发生在全球性气候突变或者转折时期,表明在这些时段季风气候变化异常,变率增大,洪水和干旱事件皆有发生。本研究对于淮河防洪减灾、水土保持及水资源开发利用,对于揭示区域气候水文变化与全球变化的响应规律,具有十分重要的科学意义和实践价值。     

全新世古洪水事件光释光测年研究——以渭河下游临潼段为例

通过对渭河下游河谷进行深入的考察,在临潼段发现全新世黄土-古土壤层里夹有古洪水滞流沉积层。在剖面系统采样并进行磁化率和粒度成分分析,从沉积学角度证明该地层记录了全新世以来古洪水事件的信息。同时,在剖面采集OSL测年样品,应用单片再生剂量法(SAR)进行红外后蓝光(Post-IROSL)释光测量,获得了7个OSL绝对年龄值,建立了全新世剖面年代深度关系曲线,确定渭河在3200～3000aB.P.之间发生特大洪水事件。综合地层学对比以及剖面磁化率和粒度等气候替代性指标分析,揭示了全新世中期向晚期转折过渡时期,气候向干旱化转折,气候不稳定,频繁波动,降水变率大,是造成渭河流域特大洪水事件发生的主要原因。     

黄河上游靖远-景泰段全新世古洪水水文学

对黄河上游靖远景泰段峡谷进行系统野外考察,在靖远县金坪村(JPC)发现典型的全新世古洪水滞流沉积物。通过光释光(OSL)测年和与黄河吉县段FJJ剖面进行地层对比,确定这期特大古洪水事件发生在 3 200~3 000 a B.P.,即全新世中期晚期气候恶化转折阶段,对应着我国历史上商末至西周早期。采用古洪水水文学方法恢复古洪水洪峰水位,并且采用比降-面积法计算这一期多次古洪水事件的洪峰流量为 16 110~17 740 m³/s。同时,根据野外调查获得 2012年7月31日黄河上游大洪水的洪痕高程,采用相同参数和方法恢复其洪峰流量,误差仅有 2.7%,表明在该河段对于古洪水水文恢复计算参数选取和计算结果是可靠的。     

汉江上游尚家河段全新世古洪水事件光释光测年研究

汉江上游是南水北调中线工程重要的水源区。通过对汉江上游河谷的详细调查,在郧县尚家河段全新世黄土-古土壤剖面上部发现一层典型古洪水滞流沉积物,对其进行了年代学和沉积学的研究。对于系统采集的样品,进行粒度分析测定,证明其为典型的古洪水滞流沉积物（SWD）,记录了古洪水事件发生的气候水文信息。采用古洪水水文学方法恢复推算出这次特大古洪水事件的洪峰流量为63 720 m3/s,其规模大于实测最大洪水。应用光释光测年（OSL）技术中的单片再生剂量法（SAR）,测得样品的年龄在940±140~3 190±100 a之间,确定古洪水SWD是汉江上游发生在1 000~900 a B.P.期间的特大洪水事件的沉积物。这期古洪水事件的发生年代对应于我国北宋/辽时期的气候恶化阶段,由于东亚夏季风环流异常变化,降水变率大,气候处于不稳定期,出现旱涝灾害频繁发生的现象。研究结果对于深入揭示河流水文系统对于全球变化的响应规律提供了新的证据。     

武汉地区ZK145钻孔沉积物磁性特征及对古洪水的记录

长江中游是我国洪灾最为严重的地区,武汉江段是长江中游防洪重点.开展武汉地区长江古洪水研究,从而延长古洪水记录具有重要意义.选择长江武汉段堤后典型湖泊钻孔——ZK145钻孔,在沉积物岩性及沉积相分析的基础上,通过对岩心磁性特征和粒度特征分析,结合AMS 14C测年,对长江武汉段全新世古洪水频发期进行了研究.根据质量磁化率、频率磁化率曲线,将钻孔划分为5个沉积阶段.再结合中值粒径和砂含量,识别出9次特大古洪水事件,其年代为:10 580~10 510,10 280~10 200,9 690~9 670,9 530~9 500,8 660~8 450,7 700~75 00,6 270~5 910,4 850~4 800,3 560~3 500 cal.a BP,其中9 700~4 800 cal.a.BP为古洪水频发期.热磁曲线分析表明,古洪水沉积物的热磁曲线在510℃附近可见较明显的峰值,主导磁性矿物为磁铁矿.研究表明,质量磁化率高值、频率磁化率低值和较粗粒径为长江武汉段堤后湖泊古洪水沉积的识别标志.      

中国西部全新世历史气侯的变化

本文在收集冰川、地质、沙漠、湖泊、树木年轮及历史文献记载等历史气候研究成果的基础上,给出了我国西部全新世以来气候变化序列。主要结果如下:1.全新世气候变化的总趋势按其演变可分为三个阶段。由中全新世向晚全新世的转变可能出现在3500年以前,比我国东部大约早500年,同时发现这种转变具有某种程度的突变性。2.全新世以来,千年尺度的气候振荡经历了6个寒冷期和5个温暖期。寒冷期分别在8700～7500a.B.P,5900～5400a.B.P,4200～3800a.B.P,3000～2700a.B.P,2000～1400a.B.P,1000a.B.P至今;温暖期分别为7500～5900a.B.P,5400～4200a.B.P,3800～3000a.B.P,2700～2000a.B.P,1400～1000a.B.P。千年尺度气候振荡的周期变化在1000～3000年之间。3.近千年来,百年尺度气候振荡的温度变化出现了6个低温期和5个高温期。低温谷值分别在公元1100's(1100～1109年),1310's,1480's,1680's,1830's,1950's;高温峰值分别在公元1220's,1390's,1570's,1780's,1900's,变化周期在120～210年之间。近千年中最冷的时期出现在17世纪中到18世纪初。近500年来,公元1480～1650年是我国西部降水最少、干旱频率最高的时期,出现了三次特大旱灾。18世纪前期是降水量较多的时期。近百年来,我国西北地区东部及华北地区出现了变干的趋势。     

渭河咸阳段全新世古洪水事件光释光测年研究

古洪水水文学研究是全球气候变化研究的前沿课题,确定古洪水事件的年代是古洪水研究的重要内容之一。对渭河流域进行深入的野外考察,在中游咸阳段阶地发现全新世黄土-古土壤层里夹有古洪水滞流沉积层,表明该地层记录了古洪水事件发生的信息。在该剖面采集光释光样品,分离提取40~63 μm石英颗粒成分,应用单片再生剂量法（SAR）进行红外后蓝光(Post-IR OSL)释光测量,获得了9个OSL年龄值。结果表明由古洪水滞流沉积层记录的特大古洪水事件发生在3 200~2 800 a B.P.之间。结合沉积样品系列的磁化率和粒度成分等气候替代性指标分析,揭示了在全新世中期向晚期转折过渡时期,渭河流域处于气候向干旱化发展的转型期,气候变化剧烈,大气系统不稳定,降水变率增大等,是导致特大洪水多发的主要原因。这也是渭河流域气候水文系统对于全球性气候恶化响应的结果。     

青海玉树地区探槽和剖面揭露的全新世含炭地层及其气候环境意义

对青藏高原东南部青海玉树地区的39个泥炭和含炭砂土样品进行了AMS14C年龄测试,这些样品来自于为研究玉树断裂开挖的2个探槽和2个剖面。通过分析泥炭层及其他含炭地层的宏观岩性及其中样品的AMS14C年龄,将玉树地区的全新世含炭地层的沉积过程划分为4个阶段:阶段Ⅰ:早全新世,10100~6000a BP,非常适宜泥炭的形成;阶段Ⅱ:中—晚全新世,6000~3500a BP,较不适宜泥炭的稳定形成,沉积物中含炭量相对减少,碎屑增加,颜色变浅;阶段Ⅲ:晚全新世阶段,3500~1500a BP。该阶段的气候总体变的更加干旱和凉爽,基本上不能形成泥炭,碎屑沉积在持续增加;阶段Ⅳ:1500a BP以来:自1500~1100a BP,气候可能更加干冷,沉积物中主要为碎屑沉积;1100a BP以来,受中世纪暖期气候变化影响,在本区许多地貌单元近地表形成一层灰黑色的炭质层。这4个阶段与红原泥炭所反映的全新世气候变化波动趋势能较一致。气候、地貌和构造因素三者共同控制本区域内泥炭和炭质层的发育和形成。     

中国西南地区中－晚全新世降温事件的石笋记录

通过对桂林响水洞、荔波董歌洞和云南宁蒗泸沽湖拉家仙人洞3根石笋进行高精度的TIM S-U系测年和氧同位素分析,建立了西南地区6000a B. P.以来的古气候变化时间序列。研究结果表明,西南地区6000a B. P.以来石笋记录的冷暖事件所反映出的古季风变化,大致可分为3个阶段: ( 1) 6000～ 4000a B. P. 间的中全新世气候适宜期,显示东亚夏季风由强盛逐渐变为减弱,气候温暖湿润;( 2) 4000～ 2100a B. P.间的中全新世晚期,是气候冷事件的突变或转换期,显示东亚冬季风增强,太阳辐射强度减弱,气温降低,气候变化幅度增大,特别是在4000～ 3500a B. P.发生的降温事件可能是新仙女木事件( Y. D)以来最为寒冷的一次降温过程,也是历史时期以来最具影响力的一次小冰期,是全新世气候演化过程中的一次重要转变, 标志着气候最适宜期的结束和晚全新世(新冰期-Neog lacial)的开始。( 3) 2100～ 130aB. P.间的晚全新世,是气候相对波动的降温期,在其内包括若干个由干冷到暖湿或由暖湿到干冷的气候变化亚期。      

江汉平原东北缘麻城剖面磁化率特征及气候环境意义

为了探讨和揭示江汉平原晚更新世以来沉积物磁学特征和该区的气候环境演变规律,对新近发现的位于江汉平原东北缘的麻城剖面进行了磁化率样品的采集和测试与对应年代学分析,结果表明:(1) 麻城剖面沉积物质量磁化率值偏低,平均值为10.85×10-8 m3·kg-1,全剖面变化不大,为5.76×10-8~23.39×10-8 m3·kg-1,但频率磁化率波动较大,分布于5.35%~50.35%,平均值为24.71%,显示具有较高的超顺磁性颗粒(super paramagnetism,SP)含量;(2) 根据磁化率和频率磁化率曲线的旋回波动特点,结合年代学测试结果,将该区的古气候环境划分为7个不同的演化阶段.初步认为该区晚更新世以来沉积环境经历了由湖沼相沉积-湖相沉积-泛滥平原中的沼泽沉积环境的变化.气候经历了温湿-干冷-暖湿-干凉-干冷-温湿-干(旱)偏冷的阶段性变化过程,与晚更新世晚期以来全球气候变化特点具有较好的一致性.      

Rhone River flood deposits in Lake Le Bourget: a proxy for Holocene environmental changes in the NW Alps, France

The Holocene evolution of Rhone River clastic sediment supply in Lake Le Bourget is documented by sub-bottom seismic profiling and multidisciplinary analysis of well-dated sediment cores. Six high-amplitude reflectors within the lacustrine drape can be correlated to periods of enhanced inter- and underflow deposition in sediment cores. Based on the synthesis of major environmental changes in the NW Alps and on the age-depth model covering the past 7500 years in Lake Le Bourget, periods of enhanced Rhone River flood events in the lake can be related to abrupt climate changes and/or to increasing land use since c. 2700 cal. yr BP. For example, significant land use under rather stable climate conditions during the Roman Empire may be responsible for large flood deposits in the northern part of Lake Le Bourget between AD 966 and 1093. However, during the Little Ice Age (LIA), well-documented major environmental changes in the catchment area essentially resulted from climate change and formed basin-wide major flood deposits in Lake Le Bourget. Up to five 'LIA-like' Holocene cold periods developing enhanced Rhone River flooding activity in Lake Le Bourget are documented at c. 7200, 5200, 2800, 1600 and 200 cal. yr BP. These abrupt climate changes were associated in the NW Alps with Mont Blanc glacier advances, enhanced glaciofluvial regimes and high lake levels. Correlations with European lake level fluctuations and winter precipitation regimes inferred from glacier fluctuations in western Norway suggest that these five Holocene cooling events at 45°N were associated with enhanced westerlies, possibly resulting from a persistent negative mode of the North Atlantic Oscillation.     

Depositional model for a chenier plain, Gulf of Carpentaria, Australia

The southern coast of the Gulf of Carpentaria, Northern Australia, consists of a broad chenier plain which is comparable in size and morphology to those reported on the coasts of Surinam and south-western Louisiana. The Carpentaria chenier plain has, at some locations, prograded over 30 km since the Middle Holocene by deposition of low-tide muds over subtidal muds during periods of increased sediment input by the rivers. Chenier ridges are formed during periods of reduced sediment flux by wave induced sorting and redistribution processes. An alternation of increased and decreased sediment flux from fluvial sources has occurred several times during the upper Holocene. Such variation in sediment supply is believed to be related to temporal fluctuations in rainfall over the drainage basin which surrounds the southern and eastern Gulf.     

白洋淀漕河全新世早期古洪水事件的沉积特征及气候背景

古洪水沉积物是研究地史时期极端降水事件和古环境演化的重要载体。基于地质记录开展古洪水重建研究,可以为揭示区域洪水历史过程及机制提供依据,对水资源利用和工程建设等具有重要的现实意义。本文以漕河古河道北岸出露较好的李迪城村剖面为研究对象,综合地层序列、野外沉积特征、沉积构造及沉积物粒度分析,对白洋淀地区漕河古河道沉积记录的古洪水事件进行了识别,发现该剖面具有以下主要特征:古洪水沉积层与下伏地层存在明显的冲刷侵蚀面,沉积体形态呈透镜状,由泥砾、炭屑、双壳类及灰黑色粉细砂混杂组成,发育中小型交错层理;洪水沉积物粒度指标(中值粒径、砂含量、黏土/粉砂值及Q90)表现为高值,以细砂为优势组分,含混杂的粉砂及少量黏土,分选较差;古洪水沉积层中古树与双壳类集中埋藏,呈定向排列,其指示的方向与遥感影像揭示的古河道方向一致。通过该剖面沉积特征及地层AMS ¹⁴C年代分析,确定漕河在全新世早期约10.8~9.6 ka BP发生了4期古洪水事件,这4期古洪水事件可以与该时期华北地区其它古洪水事件进行对比。当时正值全新世早期,东亚夏季风增强,为气温和降水频繁波动上升时期,据此推断白洋淀地区全新世早期的古洪水事件是当时气候背景下的产物。     

江汉盆地新构造运动对第四纪沉积环境演化的制约

以江汉盆地周缘区露头剖面及沉积中心区第四纪钻孔岩芯资料为研究载体,通过第四纪地层横向对比分析,恢复了江汉盆地第四纪各时期的沉积环境,讨论了江汉盆地新构造运动的特点及对江汉平原第四纪沉积环境演化的控制作用。研究表明,早中更新世江汉盆地大部处于掀升状态,盆地周缘地带遭受剥蚀;晚更新世地壳显现不等量运动,盆地自北西向中南部表现为徐缓掀升与下沉并存;全新世,盆地周缘及波状地形区掀升和低平原区强烈沉降进一步突显,全新世中晚期湖泊范围达到最大。      

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.     

Frequency and intensity of high-altitude floods over the last 3.5 ka in northwestern French Alps (Lake Anterne)

In central Western Europe, several studies have shown that colder Holocene periods, such as the Little Ice Age, also correspond to wet periods. However, in mountain areas which are highly sensitive to erosion processes and where precipitation events can be localized, past evolution of hydrological activity might be more complicated. To assess these past hydrological changes, a paleolimnological approach was applied on a 13.4-m-long sediment core taken in alpine Lake Anterne (2063 m asl) and representing the last 3.5 ka. Lake sedimentation is mainly composed of flood deposits triggered by precipitation events. Sedimentological and geochemical analyses show that floods were more frequent during cold periods while high-intensity flood events occurred preferentially during warmer periods. In mild temperature conditions, both flood patterns are present. This underlines the complex relationship between flood hazards and climatic change in mountain areas. During the warmer and/or dryer times of the end of Iron Age and the Roman Period, both the frequency and intensity of floods increased. This is interpreted as an effect of human-induced clearing for grazing activities and reveals that anthropogenic interferences must be taken into account when reconstructing climatic signals from natural archives.     

Clay mineral variations in Holocene terrestrial sediments from the Indus Basin

We employed X-ray diffraction methods to quantify clay mineral assemblages in the Indus Delta and flood plains since ~ 14 ka, spanning a period of strong climatic change. Assemblages are dominated by smectite and illite, with minor chlorite and kaolinite. Delta sediments integrate clays from across the basin and show increasing smectite input between 13 and 7.5 ka, indicating stronger chemical weathering as the summer monsoon intensified. Changes in clay mineralogy postdate changes in climate by 5–3 ka, reflecting the time needed for new clay minerals to form and be transported to the delta. Samples from the flood plains in Punjab show evidence for increased chemical weathering towards the top of the sections (6–< 4 ka), counter to the trend in the delta, at a time of monsoon weakening. Clay mineral assemblages within sandy flood-plain sediment have higher smectite/(illite + chlorite) values than interbedded mudstones, suggestive of either stronger weathering or more sediment reworking since the Mid Holocene. We show that marine records are not always good proxies for weathering across the entire flood plain. Nonetheless, the delta record likely represents the most reliable record of basin-wide weathering response to climate change.     

太湖沉积对流域极端降水和洪水响应的研究

认识极端洪水特征和周期,急需建立长期洪水记录和序列。过去150 a来长江下游极端降水引发了多次太湖特大洪水,太湖湖泊沉积提供了长于观测资料的洪水记录。本文利用太湖中心开阔水域的近现代沉积,采用210Pb和137Cs测年法和粒度、磁学特征分析,与区域夏季降水和长江下游洪峰流量进行相关分析,恢复了太湖流域150 a来的历史洪水事件。根据长江下游极端夏季降水（Pjja≥90%百分位）和极端径流(Q≥90%百分位)以及历史文献记载,太湖流域自1840年以来约有24次特大洪水年,而湖泊沉积物砂级粒径与低频磁化率等特征能捕获与之对应的中洪水事件15次。这表明湖泊沉积记录能较好地反演过去洪水变化,为利用沉积记录认识百年极端洪水长周期变化和特征提供了沉积学、磁学等方面的科学依据。