湖泊沉积记录的古洪水事件识别及与气候关系
河南三杨庄全新世以来的气候变化与洪水事件的沉积记录.pdf
目录摘要…………………………………………………………ＩＩＩＡｂｓｔｒａｃｔ．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．．、ｆｌ引言………………………………………………………．．１１．１研究的目的和意义……………………………………………１１．２孢粉学的研究进展……………………………………………２１．２．１孢粉学研究的理论基础及意义………………………………．２１．２．２孢粉学与全新世气候变迁的国内外研究进展……………………．２１．３炭屑的研究进展……………………………………………．．４１．３．１炭屑研究的基本原理及意义…………………………………４１．３．２炭屑在古环境和考古方面的国内外研究进展……………………．４１．４古洪水研究进展……………………………………………．．５１．４．１古洪水的研究意义………………………………………．．５１．４．２古洪水在环境考古方面的研究进展……．……………………．．５２研究区概况……………………………………………………．７２．１自然地理概况………………………………………………．７２．１．１地理位置………………………………………………．７２．１．２地势地貌特征……………………………………………７２．１．３地质构造………………………………………………．７２．１．４气候特征………………………………………………．７２．１．５植被特征………………………………………………．７‘２．２取样点概况…………………………………………………８２．２．１三杨庄汉代村落遗址概况…………………………………．．８２．２．２剖面位置………………………………………………．８３研究方法……………………………………………………．．１０３．１样品的采集………………………………………………．．１０３．２剖面沉积特征和岩性描述……………………………………．．１０３．３年代确定…………………………………………．．……．．１１Ｖ¨Ｉ号引入孢粉学。
湖泊水位变化与气候因素的关系研究
湖泊水位变化与气候因素的关系研究湖泊作为自然界的一个重要组成部分，其水位的变化不仅直接关系到周边生态系统的稳定性，也是研究气候变化的重要指标之一。
本文将探讨湖泊水位变化与气候因素之间的关系，以期加深我们对自然环境的认知。
首先，湖泊水位的变化是长期气候变化的体现。
气候变化主要由气温和降水变化两方面影响，而湖泊水位的变化往往是二者综合作用的结果。
在全球范围内，随着气候变暖和降水模式的改变，大多数湖泊的水位呈现出不同程度的变化。
例如，位于北极圈附近的巴伦支海，由于气候变暖导致海冰融化，其水位逐渐上升。
而一些内陆湖泊则受到干旱和水资源开发利用的影响，水位下降。
因此，湖泊水位的变化对于研究气候变化具有重要意义。
其次，湖泊水位的变化对生物多样性和生态系统功能具有影响。
湖泊是许多生物栖息的重要场所，水位的变化会直接影响湖泊内生物的栖息条件。
例如，水位的下降可能导致湖泊水源减少，水温升高，盐度增加等，进而导致湖泊生态系统的破坏和生物多样性的减少。
相反，水位的上升可能增加湖泊的湿地覆盖面积，提供更多生物栖息和繁殖的场所。
因此，湖泊水位与气候因素之间的关系不仅仅是对气候变化的响应，也影响了生物多样性的维持。
此外，湖泊水位的变化还与人类活动有着密切的关系。
随着人类经济的快速发展和人口的增加，对水资源的需求也越来越大。
为了满足人类的需要，人们进行了大规模的水资源开发利用，包括修建水库、引水渠道等。
这些人类活动不仅直接影响湖泊的水位，还可能改变湖泊的水文特征，进而影响湖泊的生态系统。
因此，研究湖泊水位变化与气候因素的关系，有助于我们更好地管理和保护自然资源。
最后，湖泊水位的变化对于社会经济也有着重要的影响。
湖泊作为一个重要的水资源储量，直接关系到周边地区的农业灌溉、供水和发电等使用。
湖泊水位的下降会导致水资源的短缺和生态环境的恶化，从而影响到当地居民的生活和经济发展。
因此，科学研究湖泊水位变化与气候因素的关系，可以帮助我们更好地预测和应对湖泊水资源的变化，为社会经济的可持续发展提供支持。
湖泊沉积的灾害事件记录与识别方法：研究进展与存在问题
李营营，李林林，何仲太. 湖泊沉积的灾害事件记录与识别方法：研究进展与存在问题[J]. 地震科学进展, 2024, 54(1): 110-123. doi:10.19987/j.dzkxjz.2023-130Li Y Y, Li L L, He Z T. Lacustrine sedimentary response to natural hazards[J]. Progress in Earthquake Sciences, 2024, 54(1): 110-123. doi:10.19987/j.dzkxjz.2023-130综述与评述湖泊沉积的灾害事件记录与识别方法：研究进展与存在问题李营营1) 李林林1, 2, 3)※ 何仲太4)1) 应急管理部国家自然灾害防治研究院，北京 1000852) 复合链生自然灾害动力学应急管理部重点实验室，北京 1000853) 中国地震局地壳动力学重点实验室，北京 1000854) 地震动力学国家重点实验室，中国地震局地质研究所，北京 100029摘要 湖泊沉积储存有丰富的信息，常被用于指示气候变化。
地震、洪水、滑坡或崩塌等自然灾害事件通常会在湖泊沉积中形成特征性的湖泊沉积扰动，可以使用湖泊地质学方法对其进行分析与识别。
本文回顾了湖泊沉积研究历程，对典型自然灾害湖泊沉积特征进行系统总结，着重梳理介绍湖泊沉积中自然灾害事件识别方法。
其中综合分析法集成了现阶段湖泊事件沉积识别的多种分析手段：①根据沉积相与异常事件沉积（EID ）之间的关系判定其内源或外源成因；②根据对触发因素的排除，确定最可能的触发因素；③根据现有的识别标准，验证最可能触发因素的正确性。
是目前识别湖泊扰动成因最有效的分析手段。
本文还对湖泊沉积灾害事件研究的优势与不足及制约因素进行讨论，湖泊沉积具有连续性、敏感性和高分辨率的特点有助于对灾害事件进行研究，但对湖泊典型自然灾害事件沉积识别标志的建立仍然是制约湖泊异常事件沉积研究的关键。
古洪水事件识别及古洪水与气候关系研究综述
古洪水事件识别及古洪水与气候关系研究综述古洪水事件是指在过去的地质时期中，发生的大规模洪水事件。
通过对古洪水事件的识别与研究，可以揭示地球历史上的气候变化、地壳运动及地理环境演变等重要信息。
本文将对古洪水事件的识别方法以及古洪水与气候关系的研究进行综述。
一、古洪水事件的识别方法1. 地质标志法：根据地下沉积物中保存的洪水相关物质和沉积结构特征进行识别。
岩层中的洪水纹理、碎屑物质的分布等可以用来判断过去是否发生过洪水事件。
2. 沉积物分析法：通过对古洪水沉积物的颗粒大小、沉积速度等参数的分析，可以判断古洪水事件的规模和性质。
大规模洪水事件往往会在沉积物中留下较大颗粒的沉积。
3. 气候指示物分析法：通过对古洪水事件沉积物中的气候指示物进行分析，可以判断古洪水事件与当地气候条件的关系。
冰川融水物质的存在可以表明古洪水事件与冰川退缩有关。
1. 气候变暖导致洪水：古洪水事件的频率和规模与当地气候条件有密切关系。
在气候变暖的条件下，冰川融水和降雨增加，导致洪水事件的发生频率和规模增加。
通过对古洪水事件的研究可以揭示气候变暖对洪水的影响。
2. 古洪水对气候的反馈效应：古洪水事件会导致区域气候的变化。
洪水事件释放大量的水汽到大气中，增加了大气的湿度，对气候变化起到一定的调节作用。
洪水事件会增加当地的降雨量，进一步加剧气候变暖。
三、研究展望古洪水事件的识别与研究是一个复杂而又重要的课题。
目前，随着科技的进步，各种新的研究方法和工具不断涌现，为古洪水事件的识别与研究提供了更多的可能性。
未来的研究可以从以下几个方面展开：1. 基于遥感数据的洪水事件识别：利用卫星遥感数据可以对大范围地区进行洪水事件的识别，提高研究的精度和效率。
2. 数值模拟与统计分析相结合的研究方法：将数值模拟与统计分析相结合，能够更准确地模拟古洪水事件的发生机制，并通过统计分析揭示洪水与气候的关系。
3. 多学科的合作研究：古洪水事件的研究需要跨学科的合作，包括地质学、气候学、地理学等。
过去1400年阿尔卑斯山西北部湖相沉积层记录的古洪水活动与气候变化
See discussions, stats, and author profiles for this publication at: /publication/243962934 Palaeoflood activity and climate change over the last 1400 years recorded by lake sediments in the NW European AlpsARTICLE in JOURNAL OF QUATERNARY SCIENCE · FEBRUARY 2013Impact Factor: 3.36 · DOI: 10.1002/jqs.2609CITATIONS 17READS 6512 AUTHORS, INCLUDING:Fabien ArnaudUniversité Savoie Mont Blanc 238 PUBLICATIONS 954 CITATIONSSEE PROFILE Pierre SabatierUniversité Savoie Mont Blanc 71 PUBLICATIONS 262 CITATIONSSEE PROFILET. CourpUniversité de Perpignan23 PUBLICATIONS 233 CITATIONSSEE PROFILEKazuyo TachikawaCentre Européen de Recherche et d’Enseig…73 PUBLICATIONS 1,479 CITATIONSSEE PROFILEAvailable from: Pierre SabatierPalaeoflood activity and climate change over thelast1400years recorded by lake sediments in thenorth-west European AlpsB.WILHELM,1*F.ARNAUD,1P.SABATIER,1O.MAGAND,2E.CHAPRON,3T.COURP,4K.TACHIKAWA,5B.FANGET,1E.MALET,1C.PIGNOL,1E.BARD5and J.J.DELANNOY11EDYTEM,Universite´de Savoie,CNRS,Poˆle Montagne,73376Le Bourget du Lac,France2LGGE,Universite´de Grenoble Alpes,CNRS,Grenoble,France3ISTO,Universite´d’Orle´ans,Observatoire des Sciences de l’Univers en re´gion Centre,CNRS,BRGM,Orle´ans,France4CEFREM,Universite´de Perpignan via Domitia,CNRS,Perpignan,France5CEREGE,Universite´Aix-Marseille,Colle`ge de France,IRD,CNRS,Technopole de l’Arbois,Aix en Provence,France Received18March2012;Revised12November2013;Accepted25November2012ABSTRACT:A high-resolution sedimentological and geochemical study of a high-altitude proglacial lake(Lake Blanc,Aiguilles Rouges,2352m a.s.l.)revealed195turbidites,190of which are related toflood events over the last 1400years.We used the coarsest sediment fraction of each turbidite as a proxy for the intensity of eachflood event.Because mostflood events at this locality are triggered by localized summer convective precipitation events,the reconstructed sedimentary record reveals changes in the frequency and intensity of such events over the last parisons with other temperature,palaeohydrological and glacier reconstructions in the region suggest that the most intense events occurred during the warmest periods,i.e.during the Medieval Climate Anomaly (AD800–1300)and the current period of global warming.On a multi-decadal time scale,almost all theflood frequency peaks seem to correspond to warmer periods,whereas multi-centennial variations inflood frequency appear to follow the regional precipitation pattern.Consequently,this new Alpineflood record provides further evidence of a link between climate warming and an increase in the frequency and intensity offlooding on a multi-decadal time scale,whereas the centennial variability inflood frequencies is related to regional precipitation patterns.Copyright#2013John Wiley&Sons,Ltd.KEYWORDS:climate change;flood frequency;flood intensity;lake sediment;last millennium.IntroductionExtreme precipitation events can triggerfloods that may have serious human and economic consequences(Gaume et al., 2009).Although theoretical studies and numerical simulations suggest that global warming will lead to an increase in the frequency and/or intensity of such events(IPCC,2007),the relationship betweenflood events and climate change is difficult to assess because the lack of long-term meteorological data at high-altitude sites(e.g.Beniston et al.,2007)and the stochastic nature of extreme events preclude the identification of long-term trends.One way of overcoming this problem is to extend documentary records beyond observational data by reconstructing long-term geological archives of intenseflood events.Such long-term records can then be used to build a better understanding of how local to regionalflood hazard patterns are likely to be affected by global warming and thereby improve predictive models(IPCC,2007,and references therein).Lake sediments are continuous archives in which it is possible to identify high-energy sediment layers and thus reconstruct mountain-riverflood records(e.g.Arnaud et al., 2002;Gilli et al.,2003;Bøe et al.,2006;Moreno et al.,2008; Storen et al.,2010;Wilhelm et al.,2012a,b).In addition,the relative intensities of palaeo-floods can be assessed from the size of the coarsest sediment fraction in eachflood layer,as sediment grain size depends on streamflow velocity(Camp-bell,1998;Parris et al.,2010).In some cases,the thickness of flood deposits can also be used as a proxy forflood intensity (Nesje et al.,2001;Wilhelm et al.,2012a,b).Few studies in the European Alps have attempted to use lake sediment records to reconstruct both the frequency and the intensity of extremefloods.The small amount of data available suggest that proglacial lakes(Stewart et al.,2011;Wilhelm et al.,2012a)are good candidates for this type of study,as they are less sensitive to the human-driven processes that often dominate climate–erosion–sedimentation interplays(Dapples et al.,2002;Giguet-Covex et al.,2011).A previous study has also reported a relationship between mountain-riverflood activity and temperature,with increasedflood frequency and intensity during warmer periods over the last250years (Wilhelm et al.,2012a).A major limitation on the use of proglacial lake sediments for studyingflood activity is the presence of plant remains for radiocarbon dating.In this respect,Lake Blanc in the Aiguilles Rouges,north-west European Alps,is an excellent locality for studying millen-nial-scale variations inflood frequency because its catchment area contains both a glacier,which delivers clastic material, and sparse vegetation.Consequently,we were able to extend our results beyond the period covered by Wilhelm et al.(2012a) and draw up a record of the frequency and intensity of extreme flood events over a time span covering both warm(Medieval Climate Anomaly,MCA)and cold(Little Ice Age,LIA)periods. By doing so we were able to test the hypothesis thatflood frequency and intensity increase during warmer periods. Study areaLake Blanc(2352m a.s.l.,4585805700N,685302000E)lies in a 1-km2proglacial cirque on the right bank of the River Arve,just north of the Mont-Blanc Range(Fig.1).The catchment consists mainly of gneiss with a small lens of sedimentary rocks(quartzite and limestone)at the top of the highest peak,the Aiguille du Belve´de`re(2965m a.s.l.).Roches moutonne´es and thick glacialJOURNAL OF QUATERNARY SCIENCE(2013)28(2)189–199ISSN0267-8179.DOI:10.1002/jqs.2609 *Correspondence:B.Wilhelm,as above.E-mail:bruno.wilhelm@univ-savoie.frdeposits indicate substantial past erosion of the substratum by theBelve´de `re Glacier.Due to glacial retreat,the glacier now occupies only 4%of the catchment,whereas glacial deposits cover approximately 30%of the catchment.Given the absence of vegetation on the glacial deposits,this larger area probablycorresponds to the maximum advance of the Belve´de `re Glacier during the LIA.Erosion of the glacier foreland and transport by a proglacial stream means the lake receives a continuous input of glacial material that has built a large delta at the mouth of the stream (Figs 1and 2)and ensures the lake waters remain turbid throughout the thaw period.From November to May,the catchment is covered by snow and the lake is frozen;therefore,nearly all sediment input occurs during the summer and early autumn.However,during the winter period lake sediments can be affected by avalanches,as shown by the exceptionally large avalanche that occurred during the winter of 1986.As well as destroying the upper floor of the old mountain hut (Fig.1),this avalanche broke the lake’s ice cover and ejected fine sediments from both Lake Blanc and a small lake located downstream (Lignier,2001,and references therein).The catchment area and the lake have very similar characteristics to another Lake Blanc,100km south of the Aiguilles Rouge,in the Belledonne Mountains (2170m a.s.l.,4581004200N,585802100E).Although the Belledonne Lake Blanccatchment is slightly larger (3km 2)than the Aiguilles Rouge Lake Blanc catchment (1km 2),the two lakes have similar climates (Kieffer-Weisse and Bois,2001),lie in steep-sided proglacial cirques consisting mainly of gneiss and have large proglacial areas as their sediment main source (Wilhelm et al .,2012a).These similarities suggest that the Aiguilles Rouges Lake Blanc is a suitable site for extending the flood record established for the Belledonne Lake Blanc.Material and methodsSeismic survey and coringThe bathymetry of the lake and the geometry of its sedimentary infill were investigated in September 2008by high-resolution seismic profiling using an INOMAR SES-2000Compact system (mean frequency of 8kHz)coupled with differential GPS navigation.Sub-bottom profiling was carried out from an inflatable boat,following a perpendicular grid with 20-m spacing between each profile (Fig.2).We used the resulting database to select coring sites in the main basin along a proximal–distal transect starting in the delta,where sedimen-tary infill is thickest and least affected by subaquatic mass-wastingprocesses.Figure 1.Left:location of Lake Blanc in the northern French Alps,close to Chamonix in the Mont-Blanc region (left).The stars show major historical earthquakes close to Chamonix and their respective magnitudes (Lambert and Levret-Albaret,1996).Right:geological and geomorphological characteristics of the catchment area.This figure is available in colour online at.Figure 2.Bathymetric map,coring sites,seismic grid and details of the NE–SW seismic profile.The seismic profile shows the positions of cores BAR10II and BAR10P04and of the four upper high-amplitude reflections labelled R1to R4,with increasing depth.This figure is available in colour online at .190JOURNAL OF QUATERNARY SCIENCEIn the winters2009and2010we retrieved one short (BAR09P1;45858058.700N,6853019.600E)and two long(BAR10I; 45858058.2700N,6853020.5300E and BAR10II;45858057.6600N, 6853021.4500E)cores from the frozen surface of the lake using an UWITEC gravity corer for the short core and a piston corer for the long cores.Multiple cores were drilled in order to obtain a second assessment of the spatial extent of the lake basin deposits that could be combined with the seismic profiles.The BAR10I(2.8m)and BAR10II(2.5m)cores both stopped at a horizon made up of semi-angular decimetre-scale blocks in the middle of the lake sediment infill.Cores BAR10I and BAR10II are composed of three and four sections,respectively,plus a short gravity-core per site(BAR10P02and BAR10P04, respectively)taken to provide well-preserved water–sediment interface samples.The deepest BAR10I section was lost and is therefore missing from the composite sequence.We con-structed composite sequences,using the thick and distinctive graded beds that appear in each section to ensure a precise and reliable stratigraphic correlation.Core description and loggingCores were split lengthwise and photographed at high resolution(20pixels mmÀ1).We examined the visual macro-scopic features of each core in detail in order to determine the different sedimentary facies,which we then used to determine the stratigraphic correlation between the cores.We calibrated the seismic data using physical measurements(P-wave velocity and gamma-ray attenuation bulk density)carried out on the Geotek TM multisensor core-logger at the Chrono-Environne-ment Laboratory.Grain size measurements were carried out on core BAR10II(Malvern Mastersizer2000)at a5-mm continu-ous sampling interval.Interbedded deposits were characterized on the basis of their median(Q50)and coarse(Q90)fractions (Passega,1964;Shiki et al.,2000;Mulder et al.,2001).We also recorded the thickness and Q90max(i.e.highest Q90value)of each interbedded deposit as a proxy for the quantity and the grain size of sediment mobilized and therefore water-current energy(Campbell,1998;Parris et al.,2010).Geochemical element analysis was carried out using X-rayfluorescence core scanner Itrax TM(Cox Analytical System)at the CEREGE laboratory,using a Chromium tube(35keV,40mA),a15-s count-time and a1-mm sampling step.The areas of the element peaks provide an indication of the relative concentrations of each element(Tachikawa et al.,2011).Among the measured elements,iron(Fe),calcium(Ca)and zirconium(Zr)were investigated as high-resolution grain-size proxies for identifying the thinnest interbedded deposits(Cuven et al.,2010;Giguet-Covex et al.,2011;Wilhelm et al.,2012a)and to help constrain the stratigraphic correlation between the three cores.Given the geology of the catchment area,Fe is probably associated with clays,Ca with feldspars in the gneiss or carbonates in the limestone,and Zr with zircons in the sediment(Lignier,2001). Dating methods137Caesium(Cs)measurements on the upper70cm of core BAR09P1were carried out at the LGGE(Grenoble).Measure-ment intervals followed facies boundaries,resulting in a non-regular sampling step of approximately1cm.The thick bed between6and24cm,which we considered an instantaneous deposit,was not analysed.137Cs was introduced into the environment by atmospheric nuclear weapon tests(AD1958–1963)and the Chernobyl accident(AD1986;Radakovitch et al.,1999);therefore,the appearance of137Cs in the sedimentary record is a reliable chronostratigraphic marker for the end of the1950s.In addition,the bases of theflood deposits contained small vegetal macro-remains,some of which were large enough to be identified as pine needles and herbaceous stems.We sent nine samples to the LMC14national carbon measurement laboratory for accelerator mass spec-trometry14C analysis.Because vegetal remains were absent from the deepest part of the sediment record,we also analysed bulk sediment in order to test the reliability of bulk sample ages. We did this by carrying out14C analyses on organic matter from a bulk sediment sample and on vegetal remains from the same sediment layer.14C ages were calibrated using the Intcal09 calibration curve(Reimer et al.,2009;Table1).The14C age for the bulk sediment sample was twice as old as the14C age for the vegetal remains from the same layer.This may be due to the presence of fossil carbon from the sedimentary rocks or older carbon from the erosion of soils.Most importantly,thisfinding meant that we were unable to obtain a reliable age for the deepest part of the sediment record.We applied the R-code package‘clam’(Blaauw,2010)to generate an age model for the most distal core(BAR10II).We then used the stratigraphic correlation(Fig.3)to recalculate the depths of all the 14C samples for this core(Table1).The most distal core was used for this purpose in order to minimize the effects on the sequence of erosion by high-energy sediment events. ResultsLake morphology and sediment infillThe seismic signal easily penetrated the regularly stratified lacustrine sediments in the main basin but became scattered and absorbed at the acoustic basement and at the north-east end of the basin,where a steep delta has developed(Fig.2).Table1.Radiocarbon age details.All cumulated and composite depths are for core BAR10II and are based on the stratigraphic correlation shown in Fig.3.The composite depth was calculated by removing graded beds,which we interpret as instantaneous deposits.Samples in italics correspond to dates excluded when building the age–depth model.See text for explanation,nature of samples and calibration procedures.Lab.code Core Core depth(cm)Cumulateddepth for coreBAR10II(cm)Compositedepth for coreBAR10II(cm)MaterialAge(14C a BP)Cal.a AD(Æ2s)SacA16864BAR09P174.5–75.541–4214.3Vegetal remains165Æ301662–1953 SacA16865BAR09P192.6–9446.5–47.517.5Vegetal remains260Æ301519–1951 SacA21322Bar10I04Ab82–8374.5–75.531.8Vegetal remains945Æ301024–1157 SacA21318Bar10II02A32–3376–7732.5Vegetal remains410Æ301431–1620 SacA21321Bar10I02Ab58–5996.5–97.548.6Vegetal remains470Æ301410–1457 SacA21323Bar10I02Ab111–112139–14066Vegetal remains765Æ301219–1282 SacA21324Bar10I02Ab111–112139–14066Bulk2035Æ30160BC–50 SacA21319Bar10I04Bb62–63169–16977.8Vegetal remains1025Æ30900–1146 SacA21320Bar10I04Bb71–72176–17781.2Vegetal remains1295Æ30663–773PALAEOFLOOD ACTIVITY IN THE NW EUROPEAN ALPS191P-wave velocity measurements on sediment cores indicate that a mean velocity of 2000m s À1should be used to estimate the thickness of the basin fill.Figure 2shows that the progradation of the delta into the lake has resulted in the development of steep foreset beds (with very limited acoustic penetration)and well-stratified bottomset beds in the deeper basin.These bottomset beds are up to 5m thick close to the delta but they quickly thin towards the lake outlet.The profile for the main basin showed several high-amplitude,sub-parallel reflections (labelled R1to R4).Close to the lake floor,we identified a transparent to chaotic lens-shaped body that is thickest at the foot of the prodelta but extends over most of the main basin.The body’s acoustic signature and form are typical of sub-aqueous mass-wasting deposits (MWD)in clastic lakes with steep slopes (Chapron et al .,1999,2007;Schnellmann et al.,2005;Fanetti et al .,2008).Lithostratigraphical descriptionThe sediment mainly consists of finely laminated silty clay sediments interbedded with a coarse-grained layer,three deformed layers and 195-mm to-centimetre-thick normally graded beds.Coarse-grained layerA 1-cm-thick coarse-grained layer is present at 158cm in core BAR10II only.This layer consists mainly of coarse sand andsmall angular gravel in a silty clay matrix (Figs 3and 4).These characteristics are highlighted by the layer’s isolated position in the Passega-type diagram,with a very high Q 90value for a low Q 50value (Fig.5).Deformed layersSome layers are characterized by a deformed structure and folded laminations.The uppermost of these layers occurs at 22–37cm in the most proximal core (BAR09P1)and is overlain by a 16-cm-thick normally graded bed (Fig.3).BAR10II,which was taken at the foot of the western steep slope,contains a second deformed layer at 55–61cm.This layer is overlain by a thin normally graded bed.The third and deepest deformed layer occurs at 258–260cm in BAR10I and corresponds to a flattened fold that duplicates a multi-millimetre-thick bed.This deformed layer is overlain by two 4-cm-thick graded beds that are identical to the two beds below the deformed layer.Graded bedsThe graded beds are characterized by their higher density,sharp,coarse-grained and occasionally erosive base,and a fining-upward trend,indicated by the synchronous decrease of Q 50and Q 90(Fig.5).Core BAR10II contained only one clear erosive contact,at the base of the thickest graded bed,at a depth of around 18cm.According to the stratigraphic correlation,all the graded beds but one extend over theentireFigure 3.Lithological descriptions of cores and stratigraphic correlation based on sedi-mentary facies,relative Ca contents and Zr/Fe ratios.Zr/Fe ratios,used as a high-resolution grain-size proxy,are shown beside the coarse percentile (Q 90).The 137Cs profile for BAR09P1is shown and available 14C samples are indicated by red and black stars.Depths of the four upper high-amplitude seismic reflec-tions shown in Fig.1(R1–R4)are given along-side core BAR10II.This figure is available in colour online at .192JOURNAL OF QUATERNARY SCIENCElake basin (Fig.3).The exception is a graded bed that occurs at approximately 60cm in BAR09P1and at 50cm in BAR10I,indicating that this layer is restricted to the deepest part of the lake basin.Furthermore,when plotted on a thickness vs.Q 90max graph,the BAR10II graded beds form two distinct clusters (Fig.5).The left-hand cluster includes most of the graded beds and is characterized by a significant thickness–Q 90max relationship (r ¼0.79,P <0.0001).The right-hand cluster consists of the four thickest beds.We interpreted the graded beds in the left-hand cluster as flood-induced turbidites,and hence they are labelled FIT in Fig.5(see Discussion).We interpreted the graded beds in the right-hand cluster as slide-induced turbidites,and hence they are labelled SIT in Figs 3and 5(see Discussion).There is a good correspondence between the depths of the high-amplitude seismic reflectionsand three of the SITs,with R1corresponding to SIT2,R2corresponding to SIT4and R3corresponding to SIT5(Figs 2and 3).High-resolution element geochemistryCalcium contentsRelative Ca contents vary little with depth,with just two well-marked peaks in the upper part of the sediment sequence (at approximately 39and 42cm in BAR10II).Although the absence of significant variations in the Ca contents of the graded beds precludes the use of this element as a grain-size proxy,the two peaks in the upper part of the sequence provide additional stratigraphic markers for correlations between the cores (Fig.3).Iron and zirconium contentsA plot of relative Fe contents vs.sediment depth (Fig.4)showed increased Fe contents for the top parts of the millimetre-to-centimetre graded beds,suggesting Fe enrichment in the finest sediment fraction (Cuven et al .,2010;Wilhelm et al .,2012a).Potassium (K),which is mainly contained in the clay fraction,and Fe are covariant (r ¼0.85,P <0.0001),indicating that changes in Fe content are mainly related to grain size,rather than to oxidation–reduction processes.This conclusion is supported by the concordance between Fe content and the <4-m m grain size fraction (Fig.4).Variations in Zr contents show the opposite pattern to changes in Fe content (r ¼–0.79,P <0.0001,between Zr and Fe),with Zr enrichment in the basal part of the graded beds and thus in the Q 90fraction (Fig.4).We found a significant correlation (r ¼0.93,P <0.0001)between the 5-mm resampled Zr/Fe ratio and the Q 90/[<4-m m fraction](Fig.4),indicating that the Zr/Fe ratio can be used as a high-resolution proxy for relative grain-size distribution and hence for detecting millimetre-scale graded beds.Dating results137Cs was present down to the base of the deformed layer at 38cm in core BAR09P1(MWD1,Fig.3).137Cs activity below this layer is null,showing that the material in the deformed layer was deposited after AD 1958.We first constructed a composite sedimentary sequence by excluding all the interbedded deposits (Arnaud et al .,2002;Moreno et al .,2008;Giguet-Covex et al .,2011),which we interpreted as instantaneous deposits formed by rapid sedi-mentary processes (see Discussion).We then calculated a depth-to-age model by linear interpolation,using the ‘clam’R-code package (Blaauw,2010).Although the results show that the sequence covers the last two millennia,because of the absence of 14C ages for the deepest part of the sediment record,the following discussion only considers the upper 190cmofFigure 4.High-resolution investigation of the relationship between geochemical (Fe and Zr)and grain size (fine fraction and Q 90)varia-tions.This figure is available in colour online at .Figure 5.Grain-size character-istics of the different sedimentary facies of core BAR10II on a Pas-sega-type diagram (A)and of graded beds on a Q 90max vs.deposit thickness plot (B).FIT,flood-induced turbidite;SIT,slide-induced turbidite.This figure is available in colour online at.PALAEOFLOOD ACTIVITY IN THE NW EUROPEAN ALPS 193BAR10II (i.e.the upper 85cm of the composite sedimentary record,Fig.6),which covers the last 1400years.DiscussionDifferent origins for the interbedded depositsAvalanche originThe local presence of coarse sand and gravel in the unsorted coarse layer at 158cm in core BAR10II (Fig.3)suggests that this layer consists of material deposited by melting ice following a dirty avalanche (Seierstad et al .,2002;Chapron et al .,2007;Guyard et al .,2007;Vasskog et al .,2011).Mass movement originThe preservation of laminae below and above the deformed layers precludes a coring origin for the deformed sediments.Naturally deformed sediment layers are usually described as MWD,formed when sediments slide down a slope to form different kinds of mass flow or turbidite (e.g.Shiki et al .,2000;Monecke et al .,2004;Schnellmann et al .,2005;Chapron et al .,1999,2007;Girardclos et al .,2007;Bertrand et al .,2008;Fanetti et al .,2008).Support for such a mass flow origin is provided by the good match between the depth and location of the thick deformed layer in BAR09P1(MWD1,Fig.3)and the MWD revealed by the seismic data (Fig.2).However,the MWD2deformed layer does not correspond to a seismically detected event.This may be because the thickness of the layer (8cm)is below the vertical resolution of the seismic data (approx.20cm)or because it is composed of less dense sediment than MWD1,which is at the foot of the delta.In addition,the duplicated sediment sequence separated by the folded layer in BAR10I can only be explained by a slide from the delta slope to the deepest part of the lake basin.Consequently,we also interpreted the folded layer and the two overlying beds as an MWD (MWD3,Fig.3).Seismic data suggest that the thick graded bed (indicated by SIT5,Fig.3)just below MWD3may correspond to high-amplitude reflection R3(Fig.2).On the other hand,graded beds are common features in lake sediments,where they are associated with turbidity currents triggered by either flood events or mass movements (e.g.Sturmand Matter,1978;Shiki et al .,2000;Arnaud et al .,2002;Gilbert et al .,2006;Mulder and Chapron,2011;Wilhelm et al .,2012a).In the latter case,they are formed by the sediment that is transported in suspension during the mass movement and then deposited over the MWD and/or further in the lake basin (e.g.Shiki et al .,2000;Schnellmann et al .,2005;Girardclos et al .,2007;Fanetti et al .,2008).Consequently,such graded beds are generally confined to a restricted area of the lake basin and often contain larger quantities of sediment than graded beds produced by flood events (e.g.Shiki et al .,2000;Schnellmann et al .,2005;Fanetti et al .,2008;Wilhelm et al .,2012a).The only well-marked graded bed is restricted to the deepest part of the lake basin (indicated by SIT3,Fig.3),suggesting that it corresponds to a slide-induced turbidite (SIT).Furthermore,the thick graded bed indicated by SIT1in Fig.3directly overlies MWD1and was therefore almost certainly produced by the deposition of sediment suspended in the water column during the mass movement that produced MWD1.The isolated position of SIT1in the thickness–Q 90max diagram (Fig.5B)also supports an SIT interpretation,with this bed representing a rare case in which a large quantity of sediment was transported without an exceptionally high current energy.Thus,MWD1and SIT1were probably produced by the same mass movement.The right-hand cluster in the Q 90–thickness diagram contains three other thick graded beds with similar characteristics to SIT1(Fig.5B),suggesting a mass movement origin for all these beds.Therefore,they are also interpreted as SIT deposits (SIT2,SIT4and SIT5,Fig.3).Flood originAll the other graded beds,which extend over the entire basin,are grouped in a distinct cluster in the thickness–Q 90max diagram and are therefore likely to have been formed in the same way (Fig.5B).A flood origin for these beds is supported by the presence of terrestrial vegetal remains within the beds and their frequent occurrence (mean recurrence time of 7years).In addition,the linear thickness–Q 90max relationship is consistent with sedimentary processes regulated by water currents,with higher discharge rates leading to greater sediment supply and coarser material.Consequently,we interpret all the 190graded beds thinner than 4cm as flood-induced turbidites (FITs).The significant relationship (r ¼0.79,P <0.0001)between thefloodFigure 6.Age–depth relation-ship for core BAR10II (left),age probabilities of the most recent MWD and SIT and possible cor-related historical events (right).This figure is available in colour online at .194JOURNAL OF QUATERNARY SCIENCE。
湖泊沉积物记录的古环境信息
湖泊沉积物记录的古环境信息湖泊是自然界中保存古环境信息的宝库。
湖泊沉积物，尤其是沉积在湖底的泥沙和有机物质，能够记录下几千年甚至上万年的自然环境变化。
通过对湖泊沉积物的细致研究，科学家们能够重建远古时期的气候、环境和生态系统，为我们理解地球的变化提供了重要的依据。
首先，湖泊沉积物可以提供关于古气候的重要信息。
湖泊中的沉积物主要由降落的泥沙和悬浮颗粒物组成，其中还包含有来源于植物和动物的有机物质。
这些沉积物在时间上层层叠加，形成了一种时间序列。
通过对不同时间层次上的沉积物的分析，科学家们可以获得古气候的重要参数，如降水量、温度、湖水水位等。
例如，深海鱼类在不同气候条件下生长的情况和组成物的含量和比例等都可以反映古气候的差异。
其次，湖泊沉积物还可以提供有关古环境和生态系统的重要信息。
湖泊生态系统是一个复杂的生物群落，由多种生物组成，包括浮游植物、浮游动物、底栖生物等。
这些生物在湖泊中生活、繁殖和死亡，它们的骨骼、背壳、花粉等遗骸可以沉积在湖底，形成一层层的沉积物。
通过对这些沉积物中的古生物遗骸的分析，科学家们可以了解古湖泊的生态系统和生物多样性，以及古环境中可能存在的压力和变化。
例如，苔藓在一些特定环境中生长丰富，而在其他环境下则相对较少，这可以为我们提供关于古生态系统的线索。
此外，湖泊沉积物还可以提供一些有关人类活动的重要信息。
随着人类的发展和活动，湖泊沉积物中有机物和重金属等人为污染物的含量也开始上升，这些污染物会在沉积物中长期保存。
通过对湖泊沉积物中的微量元素和有机物的分析，科学家们可以了解人类活动对环境的影响和湖泊的健康状况。
例如，高浓度的重金属污染物可能是工业活动或农业排放的结果，而湖泊沉积物中的有机物可能来自大量使用化肥和农药等现象。
总的来说，湖泊沉积物是一种非常宝贵的古环境信息资源。
通过对湖泊沉积物的综合分析，我们可以了解过去几千年以来地球的环境演变，包括气候变化、生态系统变化和人类活动对环境的影响等。
湖泊沉积物记录对古气候重建的价值
湖泊沉积物记录对古气候重建的价值湖泊沉积物是一种重要的地质记录，其中蕴含着丰富的信息，尤其对于古气候的重建具有重要的价值。
湖泊沉积物中的沉积物可以被视为时间的胶囊，它们记录了过去几千年甚至几百万年来的气候演变。
通过对湖泊沉积物进行分析，科学家们可以从中提取出关于古气候的各种信息，比如降水变化、温度变化、气候极端事件等，进而重建过去的气候模式。
首先，湖泊沉积物中的粒径分布可以提供关于古气候的重要线索。
湖泊沉积物的粒径分布受到多种因素的影响，包括气候、降水、水深等。
通过分析湖泊沉积物中不同粒径的组成比例，科学家们可以了解到过去的气候条件。
比如，在干旱时期，气温较高、降水稀少，湖泊沉积物中的细粒颗粒会增加；而在湿润时期，气温较低、降水增加，湖泊沉积物中的粗粒颗粒会增加。
通过对不同湖泊沉积物中粒径分布的对比和分析，可以推测出不同地区的气候变化趋势，为古气候重建提供基础依据。
其次，湖泊沉积物中的有机质含量也是重要的气候指标。
有机质是湖泊沉积物中蕴含的大量有机碳，它的含量与古气候条件密切相关。
在湿润和温暖的气候条件下，有机质的质量和数量通常较高，说明该地区的生物活动活跃；而在干旱和寒冷的气候条件下，有机质的含量则较低。
通过对湖泊沉积物中的有机质含量进行分析，科学家们可以了解到过去几千年来的气候变化趋势和生态系统动态，进而反映出古气候的变化模式。
此外，湖泊沉积物中的微生物群落也为古气候重建提供了重要的信息。
微生物是地球上最早出现的生物群体之一，在古气候的演变过程中扮演着重要的角色。
通过对湖泊沉积物中微生物群落的鉴定和分析，科学家们可以了解到过去的环境条件、气温变化和气候波动。
比如，湖泊沉积物中的特定微生物可以指示出湖泊古降水模式的演变，从而推测过去的气候变化情况。
最后，湖泊沉积物中的化学元素含量也可以为古气候重建提供一些线索。
湖泊沉积物中的化学元素含量与气候变化密切相关，不同的元素在不同的气候条件下具有不同的富集特点。
古洪水事件识别及古洪水与气候关系研究综述
安徽农学通报，Anhui Agri ，Sci ，Bull ，2019，25（12）作者简介：刘增琦（1995—），女，山东济南人，硕士，研究方向：释光年代学与环境变化。
收稿日期：2019-04-20古洪水事件识别及古洪水与气候关系研究综述刘增琦（山东师范大学地理与环境学院，山东济南250358）摘要：古洪水事件的识别是古洪水研究的关键手段，古洪水沉积物的野外特征、粒度组成特征及粒度参数、磁化率等，对于识别古洪水事件具有重要的参考价值；另外，古洪水还会造成文化遗存，在河道、文物或岩石上留下洪痕以及造成文化间断，这些都是重要的古洪水证据。
该文介绍了古洪水事件的3种识别方法，分别为地貌学方法、沉积学方法和环境考古学方法，讨论了洪水和气候变化的具体机制，有助于深入理解气候变化和古洪水事件及其时间规律性的研究以及洪涝灾害对气候变化的响应规律。
关键词：古洪水；沉积学；气候关系中图分类号TV211.1文献标识码A文章编号1007-7731（2019）12-0070-3Identification of Paleoflood Events and the Relationship between Paleoflood and ClimateLiu Zengqi（College of Geography and Environment ，Shandong Normal University ，Jinan 250358，China ）Abstract ：The identification of paleoflood events is the key means of paleoflood research.The field characteristics ，grain size composition characteristics ，grain size parameters and magnetic susceptibility of paleoflood sediments have important reference value for identifying paleoflood events.Paleoflood also causes cultural relics ，leaving flood marks on rivers ，cultural relics or rocks and causing cultural discontinuity.These are important evidence of paleoflood.This paper mainly discusses three identification methods ：geomorphology ，sedimentology and environmental archaeology ，which play an active role in determining paleoflood events.Finally ，the specific mechanisms of flood and climate change are discussed ，which will help us to understand climate change ，paleoflood events and their temporal regulari⁃ty ，as well as the response of flood disasters to climate change.Key words ：Paleoflood ；Sedimentology ；Climate Relations 洪水是一种非常普遍并且严重的自然灾害，会对人们的生活环境造成严重破坏，并且危胁着人类的生命财产安全。