Sedimentological and palaeohydrological characterization of Late Pleistocene and Holocene tufa mound palaeolakes using trenching methods in the Spanish Pyrenees          下载免费PDF全文

Xavier M. Pellicer  Juan Pablo Corella  Francisco Gutiérrez  Carles Roqué  Rogelio Linares  Domingo Carbonel  Mario Zarroca  Jesús Guerrero  Xavier Comas 《Sedimentology》2016,63(6):1786-1819

Lakes developed in the inner depressions of tufa mounds are rare geomorphic features and still poorly understood. Sedimentation in this unusual type of endorheic lake with a very restricted catchment area is highly sensitive to environmental and hydrological changes. The Isona tufa mound complex, north‐eastern Iberian Peninsula, is associated with the discharge zone of a confined artesian aquifer and comprises 11 tufa mounds consisting of an annular rimstone enclosing a central depression filled with lake deposits. Data gathered from trenches excavated in four palaeolakes located within three different morphostratigraphic units permitted a precise analysis of the geometrical characteristics and stratigraphic relationships of the deposits and provided a sedimentation model for the Late Quaternary infilling of the spring‐fed lakes. The work illustrates that trenches allow a precise characterization of the stratigraphic arrangements, lateral facies changes and deformation structures, which are not apparent in studies relying solely on borehole records, and facilitate sampling for dating and geochemical analyses. The five sedimentary facies described represent different evolutionary stages of the lakes, including: (i) carbonate‐rich palustrine deposits probably related to periods with strong hydrological seasonality; (ii) massive highly bioturbated organic ooze; (iii) banded organic carbonate‐rich facies associated with an increase in the regional effective moisture; (iv) fine‐grained quartz‐rich aeolian/slope‐wash sediments; and (v) colluvial facies deposited following the desiccation of the lakes located at higher altitudes. Geochemical and sedimentological analyses of the lacustrine sequences provided information on the palaeohydrological evolution of the Isona tufa mound complex and the palaeoenvironmental conditions of the area over the last 28 ka. Radiometric dating suggests that deposition occurred simultaneously at ca 22 ka in palaeolakes situated at different elevations. A drop in the piezometric level prompted by the opening of springs at lower altitudes probably caused the deactivation of the upper springs and the desiccation of the lakes. Arid conditions prevailed in the area during the Late Glacial and the early Holocene (28·0 to 8·5 ka bp ). More humid conditions recorded from 8·5 to 4·2 ka and again since 1·7 ka are in accordance with palaeoenvironmental reconstructions available in the Western Mediterranean since the Last Glacial Maximum.  相似文献   

Latent heat effects in subsurface heat transport modelling and their impact on palaeotemperature reconstructions     

Darius Mottaghy  Volker Rath 《Geophysical Journal International》2006,164(1):236-245

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中国北方平原盆地地下水氢氧同位素组成特征     

黄冠星  孙继朝 《地下水》2007,29(4):30-31,39

在系统收集整理中国北方河北平原、太原盆地、鄂尔多斯盆地以及银川平原的地下水氢氧同位素资料基础上,依据同位素形成演化相似性原理,对比分析同位素组成得出:深层地下水是在过去更寒冷的气候条件下形成;研究区的大气降水不但在现代气候条件下存在大陆效应和高程效应,而且在 25 kaB.P.以来的古气候条件下也存在大陆效应和高程效应;古气候条件下各盆地平原之间的蒸发强度的差异可能比现代气候条件下各盆地平原之间的蒸发强度的差异大.  相似文献   

Palynological evidence for vegetational and climatic changes from the HQ deep drilling core in Yunnan Province, China   总被引：6，自引：0，他引：6  

Xiao XiaYun  Shen Ji  Wang SuMin  Xiao HaiFeng  Tong GuoBang 《中国科学D辑(英文版)》2007,50(8):1189-1201

The high-resolution pollen study of a 737.72-m-long lake sediment core in the Heqing Basin of Yunnan Province shows that the vegetation and climate of mountains around the Heqing Basin went through six obvious changes since 2.780 Ma B.P. Namely, Pinus forest occupied most mountains around the studied area and the structure of vertical vegetational belt was simple between 2.780 and 2.729 Ma B.P., reflecting a relatively warm and dry climate. During 2.729―2.608 Ma B.P., the areas of cold-temperate conifer forest (CTCF) and Tsuga forest increased and the structure of vertical vegetational belt became clear. According to percentages of tropical and subtropical elements growing in low-altitude regions rifely increased, we speculate that the increase of CTCF and Tsuga forest areas mainly resulted from strong uplift of mountains which provided upward expanding space and growing condition for these plants. Thus, the climate of the low-altitude regions around the basin was relatively warm and humid. Between 2.608 and 1.553 Ma B.P., Pinus forest occupied most mountains around the studied area and forest line of CTCF rose, which reflects a moderately warm-dry climate on the whole. During 1.553―0.876 Ma B.P., the structure of vertical vegetational belt in mountains around the studied area became complicated and the amplitude of vegetational belts shifting up and down enlarged, which implies that the amplitude of climatic change increased, the climatic associational feature was more complex and the climate was moderately cold at a majority of the stage. During 0.876―0.252 Ma B.P., there were all vertical vegetational belts existing at present in mountains around the studied area. The elements of each belt were more abundant and complex than earlier. At different periods in the stage vertical vegetational belts occurred as expanding or shrinking, and alternated each other. The amplitude of vegetational belts shifting up and down was the maximum in the whole section. This change suggests that the amplitude of climatic change was evidently larger than earlier, but the frequency reduced and the climatic associational feature was more complex. From 0.252 Ma B.P. to the present, the most time was characteristic of the expanding of Pinus forest and semi-humid evergreen broad-leaved forest (SEBF) in mountains around the studied area, while expanding time of other vegetational belts was very short, which reflects a smaller amplitude of cold and warm fluctuation. On the basis of the six obvious cycles of vegetational and climatic changes, there were still many times of secondary vegetational successions and climatic oscillations. Based on the above analysis, the forcing mechanism of vegeta-tional succession and climatic change in the Heqing Basin is further discussed. It is primarily consid-ered that main influential factors were exterior factors such as orbital parameters, etc., but the uplift of the Qinghai-Tibet Plateau played a very important function for environmental changes in the Heqing Basin at two times obvious increase of vertical vegetational belts and three climatic transitions.  相似文献   

Palaeohydrological reconstructions achieved from palaeoclimatic conditions and palaeochannel morphology for southern Hebei, the North China Plain     

WANG Hong-y  XIE Qiang 《地理学报(英文版)》1999,(1)

lintroductionPalaeoh}'drolog}'dealsti'ithdieac.atersofaleeartheircompositionsdistribuhonand"lovementonancientlandscapesfrom1lieoccurrenceofthefirstrainfalltothebeginningofhistoricalllydrologicalrecordsl'].Runoffanddischargeareimportanthydrologicalpazametersdescribingquanhtyrstatusofsurfacexvater.TheirreconstrUchonsfortheQuatemmppastareillusverysigrmcantforfurtherunderstanclingtilepalaeohydrologicalcondjhonandeventhewholephysicalPalaeoenviromnentofthisgeologicalperiod.SouthernHebei(114~l17T.3…  相似文献   

50万a来沙漠-黄土边界带的环境演变   总被引：7，自引：1，他引：7  

孙继敏  丁仲礼  刘东生 《干旱区地理》1995,18(4):1-9

毛乌素沙漠与黄土高原接壤的沙漠－黄土边界带以其特有的古风成才－黄土－古土壤沉积系列记录了这一地区约50万a以来的环境演变．地层中的埋藏古风成砂是在冬季风极为强大时堆积的，古土壤是在冬季风萎缩、夏季风强盛时发育的，而黄土则是在上述两种极端气候的过渡状态下堆积的．研究结果表明毛乌素沙漠至少在50万a前就已经形成，但也并不是从一出现就持续至今，而是在第四纪气候振荡的作用下，历经“沙漠－非沙漠”的多次转变，其中沙漠明显扩大的时期至少有13次．  相似文献   

Pedogenic and lithogenic contributions to the magnetic susceptibility record of the Chinese loess/palaeosol sequence   总被引：1，自引：0，他引：1  

Pinchas Fine  Kenneth L. Verosub  Michael J. Singer 《Geophysical Journal International》1995,122(1):97-107

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云南鹤庆盆地2.780~1.802MaB.P.期间的 古植被和古气候^*   总被引：3，自引：1，他引：2  

肖霞云  沈吉  肖海丰  王苏民  童国榜 《第四纪研究》2007,27(3):417-426

鹤庆深钻421.7m以下岩芯的孢粉组合揭示2.780~1.802MaB.P.期间鹤庆盆地周围山地植被类型的更替主要是松林和寒温针叶林林带的上下迁移,并且研究区在第四纪之前就已基本具备了目前的主要植物种类及其自然地理轮廓。根据孢粉组合中寒温针叶林主要成分的孢粉含量变化推测研究区周围的山顶气候在2.780~1.802MaB.P.期间依次经历了相对温和偏干→整体相对寒冷潮湿→温和偏干→寒冷较湿→温凉较干→温和偏干→寒冷较湿的7次明显波动;同时结合孢粉组合特征和山顶气候推测盆地周围较低海拔区的气候经历了温暖干旱→整体相对温暖潮湿→温暖干旱→温凉较湿→温和偏干→温暖干旱,但夏季有一定降雨→温凉较湿的7次明显波动。在重建古植被与古气候时,还根据孢粉组合中寒温针叶林的主要成分与喜热成分的孢粉含量变化,探讨了2.780~1.802MaB.P.期间不同时段导致研究区周围山地垂直植被带迁移的主要原因,即区分了构造抬升与气候变化对其影响的可能性。研究认为2.729~2.608MaB.P.期间寒温针叶林面积增加主要是由于山体强烈抬升造成的,此次山体强烈抬升正对应着晚新生代地质时期青藏高原强烈隆升的"青藏运动B幕",而其他时段的寒温针叶林面积增减主要是气候变化引起的。  相似文献   

川西南地区五峰—龙马溪组黑色页岩古气候及物源特征: 来自新地2井地球化学记录^*          下载免费PDF全文

牟传龙  葛祥英  余谦  门欣  刘伟  何江林  梁薇 《古地理学报》2019,21(5):835-854

晚奥陶世—早志留世之交是地球历史时期中的关键时段,该时段伴有全球生物大灭绝、冈瓦纳冰川以及火山事件。晚奥陶世末期的冰川事件历时相对较短,在中国尚未找到冰川存在的直接证据。为了更好地研究奥陶—志留纪交替时期是否存在古气候的变化,选取了川西南地区新地2井岩心中新鲜的上奥陶统五峰组—下志留统龙马溪组泥页岩样品,通过其主量、微量及稀土元素特征分析,采用多种化学风化指数判定源区风化作用强度及古气候条件。新地2井五峰—龙马溪组所有岩石样品成分变异指数(ICV)均大于1,表明源岩成分成熟度低,属构造活动时期的首次沉积。稀土元素表现为轻稀土富集、重稀土平坦并伴有明显的负Eu 异常,配分模式与花岗岩相似,表明源岩以亲花岗岩、长英质为主;A-CN-K图解、主量元素Al₂O₃/TiO₂值、微量元素Cr/Zr值和Th/Sc值也体现长英质成分为主的物源特征。化学蚀变指数(CIA)、化学风化指数(CIW)和斜长石蚀变指数(PIA)等多种化学风化作用指标均指示,晚奥陶世—早志留世古风化作用强度经历中等—低等—中等、古气候温暖湿润—寒冷干燥—温暖湿润的变化过程。CIA指数的低值指示的五峰组顶部(平均值64.14)、观音桥组(平均值61.7)和龙马溪组底部(平均值64.61)即赫南特期存在短暂的寒冷气候,间接证实了冈瓦纳冰川作用在中国华南地区存在相应的地球化学记录。  相似文献   

Dryland continental mudstones: Deciphering environmental changes in problematic mudstones from the Upper Triassic (Carnian to Norian) Mercia Mudstone Group,south‐west Britain     

Paul Milroy  V. Paul Wright  Michael J. Simms 《Sedimentology》2019,66(7):2557-2589

The sedimentology, petrography and mineralogy of the seemingly monotonous Late Triassic Mercia Mudstone Group across the Severn Basin and Bristol Channel region reveals a bipartite division of mudrock facies above and below the Arden Sandstone Formation. Frequently cryptic sedimentary and pedogenic features reveal diverse alluvial, aeolian, playa‐lacustrine and pedogenic processes operating at different times, locations and scales probably in response to climate change. The current study found no evidence of significant marine influence in either of the two mudrock facies associations that are described here. Blocky claystones dominate the lower Mercia Mudstone Group (Sidmouth Mudstone Formation), with pedogenic features such as slickensides, mottling, tubules and carbonate/sulphate nodules common and widespread. The claystones are of alluvial/lacustrine origin with subordinate sheet sandstones, themselves overprinted by pedogenic features, reflecting occasional high intensity rainfall events. These facies reflect a seasonal (wet/dry) semi‐arid climate favouring development of transformed/neoformed (smectite‐rich) clay minerals of intrabasinal origin. Massive to weakly stratified silty mudstones dominate the upper Mercia Mudstone Group (Branscombe Mudstone Formation). Commonly conchoidally weathered, locally gypsiferous, but with distinct sedimentary structures scarce, they alternate with subordinate blue‐grey laminated silty mudstones. Together they reflect fluctuating hydrological conditions within extensive saline mudflats and ephemeral playa lakes, with laminated facies deposited under subaqueous conditions during more humid phases whereas massive mudstones reflect modification through interstitial growth/dissolution of sulphates and deflation of surface sediments during drier episodes. These facies reflect increased aridity during deposition of the upper Mercia Mudstone Group compared with the lower Mercia Mudstone Group, favouring development of detrital/transformed (illite–chlorite) clay minerals of extrabasinal origin. The described facies associations and the sedimentary fabrics and structures that characterize them, occur widely in the Mercia Mudstone Group across the United Kingdom and comparable facies associations may be anticipated in other fine‐grained red bed successions. Recognition of these facies may aid palaeoenvironmental interpretation of such sequences on Earth and, potentially, on Mars also.  相似文献