贵州荔波地区2000年来石笋高分辨率的气候记录

通过对荔波董哥洞石笋进行高精度的ICP MS或TIMS U系测年和碳、氧同位素分析,建立了荔波地区2 300a B.P.来高分辨率的古气候变化的时间序列。研究结果表明,贵州荔波地区2 300a B.P.以来石笋记录的季风气候变化,大致可分为8个气候(亚)期:① 2 300～1 800a B.P.为降温期,显示东亚夏季风减弱,东亚冬季风增强,气候干旱寒冷;② 1 800～1 080a B.P.气温有所回升,显示东亚冬季风缓慢减弱,东亚夏季风有所回升,表现为半湿润的温凉气候期;③ 1 080～680a B.P. 为降温期,气温再次下降,显示东亚冬季风再次增强,但降水相对增大,表现为寒冷湿润的气候期,是气候变化的关键转折时期;④ 680～550a B.P.温暖期,显示东亚夏季风再次增强,气温升高,降水增大,表现为温暖湿润的气候期。⑤ 550～400a B.P.寒冷期,显示东亚冬季风快速增强,气温下降,表现为寒冷湿润的气候环境,是近1 000年以来最冷的时期;⑥ 400～364a B.P.温凉期,显示东亚夏季风有所增强,气温有所回升,表现为温凉湿润气候环境;⑦ 364～324a B.P.冷凉期,显示东亚夏季风有所减弱,气温有所下降,表现为冷凉湿润气候环境;⑧ 324a B.P.至今,气候相对波动期,同位素记录曲线呈锯齿状波动,在其内包括若干个冷凉半湿润、冷湿的气候变化亚阶段。根据荔波董哥洞石笋的高分辨率的古气候变化的连续记录,揭示了荔波地区2 300a B.P.以来的一些百年尺度的重大气候事件——干旱寒冷期、隋唐温暖期(或小温暖期)、小寒冷期以及一些十年尺度的降水、温度变化。石笋记录的这种百年、十年尺度的突发性气候变化事件,与冰芯记录极为相似,反映低纬度地区石笋记录的季风气候与高纬度及北极地区的气候具有极好的相关性,这对于认识现代气候系统变化以及对未来十年—百年尺度的气候预测和演化的驱动机制,具有重要的科学意义。     

贵州荔波1200年来石笋高分辨率的古气候环境记录

通过笔者对荔波龙泉洞L2石笋进行高精度的ICP-MS-230Th测年和碳、氧同位素分析, 建立了荔波地区1200 a BP 来高分辨率的古气候变化的时间序列。研究结果表明, 荔波地区1200 a BP以来石笋记录的季风气候经历了1200~1100 a BP(暖)、1100~940 a BP (冷)、940~840 a BP(暖)、840~700 a BP(冷)、700~450 a BP(暖)、450~300 a BP(冷)、300~200 a BP(暖)以及200~70 a BP(冷)等8个阶段百年尺度的干湿、冷暖波动, 并在这些百年尺度的波动上又叠加了一系列数十年尺度的气候变化。石笋记录揭示了1200 a以来东亚季风气候的不稳定性, 呈百年尺度(Gleissberg)的周期性变化。这些气候变化事件, 与冰芯记录极为相似, 反映低纬度地区百年尺度石笋记录的季风气候变化与高纬度及北极地区的气候变化具有极好的相关性, 反映百年尺度石笋记录的季风降水主要受太阳辐射驱动、控制, 而东亚季风的降水事件(或干旱事件)与太阳的辐射强度密切相关。石笋记录的百年尺度季风降水事件对于认识现代气候系统变化以及对未来十年—百年尺度的气候预测和演化的驱动机制, 具有重要的科学意义。     

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。      

MIS 3晚期东亚季风强度和DO事件年龄

基于神农架山宝洞石笋(SB46)的9个230Th年龄和326个氧同位素数据,建立了末次冰期32.2～26.7kaB.P.和17.0～15.4kaB.P.的东亚季风降水序列。该序列和同一洞穴全新世石笋记录的对比发现,在MIS3晚期东亚季风区可能存在极强夏季风降水事件,相当于全新世季风强度,可能与岁差旋回太阳辐射及海陆水汽潜热释放增强有关。与葫芦洞石笋δ18O记录和格陵兰冰芯δ18O记录对比表明,东亚夏季风千年尺度气候振荡与高北纬地区海-气快速重组存在遥相关效应。山宝洞石笋年龄与葫芦洞石笋和格陵兰冰芯时标(SS09sea)在定年误差范围内基本一致,但山宝洞石笋与冰芯记录在DO事件的年龄、波形和持续时间上更为一致,不仅进一步说明了低纬季风气候与极地气温同步变化,而且有效地弥补了葫芦洞记录在这一时段的不足。     

云南寻甸地区最近八千年气候环境变迁

通过对云南寻甸白石岩仙人洞1号石笋进行高精度TIM S-U系测年和氧碳稳定同位素分析,重建了寻甸地区中全新世8. 0ka 以来高分辨率古气候演化序列。石笋剖面的碳氧同位素记录揭示,云南寻甸地区自8. 0kaB. P.以来的气候演化可以分为三个气候期: (1) 8000～6000aB. P.为温暖湿润期,夏季风强盛,气温较高,降水丰沛,石笋的氧碳同位素偏负; ( 2) 6000～5200 a B. P.为季风气候衰退期,在这期间气温和降水都发生了较大变化,气候由温湿变为冷干,石笋氧碳同位素持续偏正; ( 3) 5200～2100aB. P.凉干气候期,这一时期气候基本稳定,东亚季风对气候影响较大,但气温和降水都低于第一个气候稳定期。      

赣北石笋记录的新仙女木事件

新仙女木事件(Younger Dryas,简称YD)是末次冰消期升温过程中发生的一次北半球急剧降温事件,目前全球范围多个地区的地质记录中均有发现该事件的印记.然而,受限于定年误差或采样分辨率等因素,关于YD事件的精确起止时间、精细内部结构和触发机制仍存在争议.本研究利用江西北部神农宫溶洞内一支文石石笋SN29(总长度426 mm,其中距离顶部220~388 mm用于本研究),通过高精度 230Th定年和氧、碳稳定同位素测试分析,建立了13614~10811 a B. P.期间平均分辨率12年的石笋氧同位素(δ18O)变化序列.该记录最为显著的特征是δ18O值在12851~11575 a B. P.时段偏正1. 7‰,指示了一次显著的弱季风突变事件,响应于北大西洋YD事件. SN29为高铀含量文石石笋且生长速率较快,精确界定了响应于YD事件的东亚弱季风事件的起止时间和精细内部结构.结果表明: YD期间, SN29记录的东亚弱夏季风事件的开始时间为 12851±16 a B. P.,经历了约249年;结束过程开始于11575±19 a B. P.,经历了约146年;整个YD弱季风事件共持续了 1276±35年.东亚季风区各石笋δ18O记录的YD弱季风事件在误差范围内基本一致,且与格陵兰冰芯δ18O记录和低纬度其他记录的发生时间一致,支持YD时期东亚夏季风减弱事件可能是对大量淡水进入北大西洋导致径向翻转流减弱、北半球变冷、ITCZ南移的快速响应的假说.     

汉江上游I级河流阶的形成及对东亚季风 变化的响应

对郧县—白河段汉江Ⅰ级河流阶地上风成黄土的沉积学、理化性质、地球化学和年代学进行了系统研究。结果表明,汉江Ⅰ河流阶的形成不晚于25 ka BP;黄土具有马兰黄土(L1)→过渡黄土(Lt)→古土壤(S0)→全新世黄土(L0)→表土(TS)的地层序列,与渭河谷地的黄土地层序列完全可比;25~11.5 ka BP,冬季风强盛,气候冷干,从11.5 ka BP开始,冬季风逐渐减弱,气候开始向暖湿方向逐步转化,从8.5 ka BP开始,夏季风达到了末次冰期结束后的鼎盛时期,3.1 ka BP前后,东亚季风格局发生变化,夏季风减弱,重新进入一个相对干冷的时期,而人类活动对地表的影响形成了表土;汉江上游谷地黄土记录的末次冰期后季风逐渐加强、中全新世季风强盛、随后季风衰退和气候变干的夏季风演变模式与渭河谷地黄土的记录高度一致,与邻区石笋和泥炭记录的季风变化趋势也有良好的可比性,但与石笋/泥炭记录的夏季风强盛期的起始时间(9.3~4.2 ka BP)并不完全一致。     

东亚季风“2.8ka”事件高分辨率的石笋记录

据湖北省神农架永兴洞一支石笋的8个230Th年龄、648个δ18O数据,建立了晚全新世4.40～ 1.75ka B.P.时段平均分辨率为4a的东亚夏季风演化序列,其中在2.92～ 2.74ka B.P.期间,δ18O发生显著正偏,幅度达2.5‰,指示一个显著的弱季风事件(这里称之“2.8ka”事件).该事件以夏季风缓慢减弱开始,迅速增强结束,事件内部有两个次一级的振荡旋回(两峰三谷结构),在内部细节与转型特征上类似湖北和尚洞石笋δ18O记录的“8.2ka”事件,暗示发生在全新世这两个冷事件的驱动机制基本一致.这两个弱季风事件都发生在太阳活动明显减弱时期,并分别与北大西洋Bond 2和Bond 5冰漂碎屑事件同步,表明百年尺度的东亚季风环流的演化由太阳活动和北高纬气候共同驱动.     

小冰期东亚夏季风快速变化特征:湖北石笋记录

研究小冰期的结构特征及动力机理有助于理解全球增暖和极端气候事件的原因。基于湖北永兴洞总长为120 mm的YX275石笋7个高精度230Th年龄和120个氧同位素数据,重建了1361~1955 A.D.时段分辨率达5 a的东亚夏季风降水变化序列。该石笋δ^18O值在-7.8 ‰^-9.3 ‰范围内波动,长期趋势呈现出先缓慢增大后减小的变化特征,整体呈下凹形态。该记录与中国季风区北部和南部石笋记录变化大体一致,指示小冰期发生时东亚夏季风水循环发生减弱变化。在百年-数十年尺度上,YX275石笋记录的小冰期内5次显著季风降水减弱事件与南部贵州董哥洞、织金洞石笋记录变化一致,但不同于北方大鱼洞、九仙洞、黄爷洞和万象洞石笋记录的5次小幅度季风旋回特征,表明小冰期时中国南北部夏季风降水在短时间尺度上可能存在着区域差异。该记录与太阳总辐照度记录和北半球温度记录变化一致,表明太阳总辐照度和北半球温度变化对东亚夏季风水文变化有重要驱动作用。     

末次水消期以来气候期划分的准确定位与定年

对贵州荔波董歌洞D4石笋的再次高密度230Th测年及碳、氧同位素分析，在16 ka 以来的部分，平均分辨率达 18a 。研究表明，氧同位素记录除反映季风的强弱变化外，能更好地揭示 H1，BA，YD以及全新世中 9.1ka，8.2ka、4.6ka 气候突变事件。碳同位素记录和沉积速率则能更好地反映气候干湿的变化。石笋记录对气候期的正确划分及突变事件的准确定位及定年，可为全球变化其他记录的研究提供一个可靠时间系列的基准标尺。     

新一代天气雷达背景场特征资料生成方法及检验

地形对波束遮挡是影响雷达观测资料质量的重要误差源之一。国家防汛抗旱指挥系统二期工程建设了天气雷达应用系统,系统利用新一代天气雷达背景场特征资料客观分析技术计算出雷达站周围环境对雷达波束造成遮挡影响的背景场特征资料(挡角图、等射束高度图和波束遮挡能量耗损率图)。详细介绍了新一代天气雷达背景场特征资料计算原理和方法,并提出利用雷达回波概率特征方法,将计算出的背景场特征资料与不同仰角雷达回波统计的概率空间分布进行对比分析,验证了新一代天气雷达背景场特征资料的正确性,为后期雷达波束能量遮挡进行定量订正提供依据。     

岩溶泉流量衰减曲线分析

由于岩溶含水介质的强烈非均质性和各向异性,如何有效认识岩溶含水层内部的水文地质特征为研究难点之一,岩溶泉衰减曲线分析为认识岩溶含水层的一种有效手段。总结了目前广泛用于泉流量衰减曲线分析的几种常见方法,主要包括指数型衰减、非指数型衰减分析方法以及综合型的衰减曲线分析方法,讨论了管道可能对泉流量衰减曲线的影响,最后提出了今后对岩溶泉流量衰减曲线分析拟解决的一些关键问题。     

Evidence for a Variscan suture zone in the Vendée, France: a petrological study of blueschist facies rocks from Bois de Cené

Abstract In the Bois de Cené area, blueschist facies rocks, characterized by glaucophane and/ or chloritoid, provide evidence for a suture zone in the Variscan. This terrain is considered to be the eastern equivalent of the Ile de Groix high-pressure metamorphic terrain. Petrological study of the two characteristic types of rocks found in the area shows that the primary high-pressure paragenesis was modified during a retrogression which followed substantial decompression, probably at constant or decreasing temperature. The simplest interpretation is that this retrogression followed tectonic emplacement within a nappe pile.     

Last interglacial (MIS 5e) sea-level determined from a tectonically stable,far-field location,Eyre Peninsula,southern Australia

The last interglacial maximum (Marine Isotope Substage 5e [MIS 5e], 128–116 ka) is a distinctive event in recent Earth history. Shoreline successions of this age are important for calibrating climate models and defining the overall behaviour of the crust–mantle system to fluctuating ice and ocean-water volumes. In a global context, the recently intensified interest in last interglacial shoreline successions has revealed considerable variability in the magnitude of sea-level rise during this time interval and highlighted the need to examine paleosea-level evidence from tectonically stable, far-field settings. Situated in the far-field of continental ice sheets and on the tectonically stable Gawler Craton, the 300 km coastal sector of western Eyre Peninsula between Fowlers Bay and Lake Newland in southern Australia represents an important region for defining the glacio-eustatic (ice-equivalent) sea-level attained during the last interglacial maximum based on the relative sea-level observations from this region. Low-energy, shoaling upward, peritidal bioclastic carbonate successions of the last interglacial (locally termed Glanville Formation) formed within back-barrier, estuarine–lagoonal environments in the lee of eolianite barrier complexes (locally termed Bridgewater Formation) along this coastline. The well-preserved shelly successions (coquinas) contain diverse molluscan fossil assemblages including species no longer living in the coastal waters of South Australia (e.g. the Sydney cockle Anadara trapezia and the benthic foraminifer Marginopora vertebralis). The extent of amino acid racemisation (a measure of fossil age based on increasing d/l value) in a range of species, and in particular A. trapezia and Katelysia sp., confirms the time equivalence of the isolated embayment-fill successions, correlated with the informal type section of the Glanville Formation at Dry Creek, north of Adelaide. Preliminary U-series analyses on A. trapezia also suggest a correlation with the last interglacial maximum, but further highlight the complexity in dating fossil molluscs by the U-series method in view of their open-system behaviour. The shelly successions of the Glanville Formation occur at elevations higher than attained by sea-level in the current, Holocene interglacial. A higher sea-level of between 2.1 ± 0.5 and 4 ± 0.5 m above present sea-level is inferred for the last interglacial maximum (MIS 5e) along this coastline based on the elevation of sedimentary successions host to the shallow subtidal–intertidal fossil molluscs Katelysia sp., and Anadara trapezia. The paleosea-level observations place a lower limit on the sea-level attained during the last interglacial maximum and suggest that caution be exercised in the definition of the upper limit of sea-level during this interglacial.     

Architecture of a coarse‐grained channel–levée system: the Rosario Formation,Baja California,Mexico

Seafloor images of coarse‐grained submarine channel–levée systems commonly reveal complex braid‐plain patterns of low‐amplitude bedforms and zones of apparent bypass; however, mechanisms of channel evolution and the resultant channel‐fill architecture are poorly understood. At Playa Esqueleto the lateral relationships between various elements of a deep‐marine slope channel system are well‐exposed. Specifically, the transition from gravel‐dominated axial thalwegs to laterally persistent marginal sandstones and isolated gravel‐filled scours is revealed. Marginal sandstones pass into a monotonous thin‐bedded succession which built to form relatively low‐relief levées bounding the channel belt; in turn, the levées onlap the canyon walls. Three orders of confinement were important during the evolution of the channel system: (i) first‐order confinement was provided by the erosional canyon which confined the entire system; (ii) confined levées built of turbidite sandstones and mudstones formed the second‐order confinement, and it is demonstrated that these built from overspill at thalweg margins; and (iii) third‐order confinement describes the erosional confinement of coarse‐grained thalwegs and scours. Finer‐grained sediment was transported in suspension and largely was unaffected by topography at the scale of individual thalwegs. Facies and clast analyses of conglomerate overlying channel‐marginal scours reveal that they were deposited by composite gravity flows, which were non‐cohesive, grain‐dominant debris flows with more fluidal cores. These flows were capable of basal erosion but were strongly depositional; frictional freezing at flow margins built gravel levées, while the core maintained a more fluidal transport regime. The resultant architecture consists of matrix‐rich, poorly sorted levées bounding better‐sorted, traction‐dominated cores. The planform geometry is interpreted to have consisted of a low‐sinuosity gravel braid‐plain built by accretion around mid‐channel and bank‐attached bars. This part of the system may be analogous to fluvial systems; however, the finer‐grained sediment load formed thick suspension clouds, probably several orders of magnitude thicker than the relief of braid‐plain topography and therefore controlled by the levées and canyon wall confinement.     

半干旱半湿润地区洪水预报模型适用性研究

针对半干旱半湿润地区的流域特性和产汇流特点,比较了河北雨洪模型和新安江模型的模型原理和模型特性,以滦河支流老牛河流域为例,开展了洪水预报适用性研究。结果表明,河北雨洪模型的预报精度较高,更适用于半干旱半湿润地区的洪水预报。     

A new record of Pleistocene hippopotamus from River Severn terrace deposits, Gloucester, UK—palaeoenvironmental setting and stratigraphical significance

A new Pleistocene vertebrate assemblage from fluvial deposits of the River Severn in Gloucester, England, has yielded the remains of hippopotamus (Hippopotamus amphibius), a new record for this terrace system, with additional material from probable bison (cf. Bison priscus) and elephant (Elephantidae sp.). The presence of these taxa indicates fully temperate climatic conditions and the occurrence of hippopotamus, a significant biostratigraphical indicator for the British Late Pleistocene, suggests an age for the assemblage within MIS 5e (the Last Interglacial). This would contradict the older MIS 7-6 age for the gravel body that is currently accepted on the basis of deposit mapping and imply a more complex mode of deposition than presently envisaged in the valley.     

Un réseau fluviatile d'âge Burdigalien terminal dans le Sud-Est de la France : remplissage,extension, âge,implications

An integrated study combining facies analysis, multiple group biostratigraphy, identification of depositional sequences and mapping has been conducted on the Miocene Molasse Basin of the external Alps (southeastern France). The filling of the basin is described as resulting from a succession of fluvial incisions subsequently filled during marine transgressions. The major incision is dated as Latest Burdigalian and the major transgression as Langhian. This revised interpretation of the Miocene physiographic evolution of the Molasse Basin implies a re-examination of previous stratigraphic correlations within the basin. To cite this article: D. Besson et al., C. R. Geoscience 337 (2005).     

松嫩平原哈尔滨地区地下水环境背景值分析

受自然条件及人类活动的影响,地下水环境发生了较大的变化,地下水污染问题日益引起广泛的关注。正确确定背景值对地下水污染评价十分重要。以收集的松嫩平原哈尔滨地区150余组地下水水化学样品分析数据为依据,在分析区域流场、补给径流条件的基础上,选用数理统计法和经验法求取了研究区潜水和承压水地下水环境背景值,并对地下水环境背景值进行比较。结果表明:数理统计法以自然地理环境和人类长期活动的综合作用为基础,克服了经验法的不足,可较真实地反映研究区地下水背景状况;研究区内潜水中指标NO3-、Fe、Mn和承压水中指标Fe、Mn均为高背景值指标;区内地下水环境背景值与人类活动、地下水的补、径、排和沉积环境条件具有密切的关系。     

Late Quaternary climate-driven environmental change in the Larsemann Hills, East Antarctica, multi-proxy evidence from a lake sediment core

Little is known about the response of terrestrial East Antarctica to climate changes during the last glacial-interglacial cycle. Here we present a continuous sediment record from a lake in the Larsemann Hills, situated on a peninsula believed to have been ice-free for at least 40,000 yr. A mutli-proxy data set including geochronology, diatoms, pigments and carbonate stable isotopes indicates warmer and wetter conditions than present in the early part of the record. We interpret this as Marine Isotope Stage 5e after application of a chronological age-depth model and similar ice core evidence. Dry and cold conditions are inferred during the last glacial, with lake-level minima, floristic changes towards a shallow water algal community, and a greater biological receipt of ultraviolet radiation. During the Last Glacial Maximum and Termination I the lake was perennially ice-covered, with minimal snowmelt in the catchment. After ca. 10,500 cal yr B.P., the lake became seasonally moated or ice-free during summer. Despite a low accumulation rate, the sediments document some Holocene environmental changes including neoglacial cooling after ca. 2450 cal yr B.P., and a gradual increase in aridity and salinity to the present.