内蒙古东南缘晚第四纪以来的气候环境演化

基于内蒙古东南缘西拉木伦河上游刘家店河湖相剖面的粒度、磁化率、微量元素地球化学指标,重建该区35 ka BP以来的气候演化过程。结果表明,在MIS 3晚期(35.23~25.15ka BP)研究区气候条件总体温暖湿润,并伴有区域变干的趋势;MIS 2阶段(25.15~11.13 ka BP)气候整体寒冷干燥,但叠加有短暂回暖气候事件。剖面记录的末次盛冰期(LGM)出现于22.25~18.47 ka BP,此时气候极度干冷;MIS 2阶段叠加了两个短暂气候适宜期,分别出现于18.47~16.24 ka BP和14.72~11.13 ka BP。在11.13 ka BP前后研究区进入全新世,气候变得暖湿。刘家店剖面的气候记录与周边气候记录具有可对比性,揭示了区域上东亚夏季风进退具有一致性,并认为自MIS 3晚期以来东亚夏季风受北半球太阳辐射及冰量的共同驱动。此外,刘家店剖面记录揭示的千年尺度气候变化对典型气候事件具有一定的响应,推测这些千年尺度的季风强度变化可能与北大西洋经向翻转环流(AMOC)相关。     

Palaeoclimatic cycles, global environmental changes and new glacial periods induced by the impact of extraterrestrial bodies

In terms of Earth-Sun geometry, the Milankovitch theory has successfully explained most of the cyclic palaeoclimatic variations during the history of the Earth, especially in the Quaternary. In this paper, the authors suggest that the impact of extraterrestrial bodies on the Earth may be another mechanism to cause palaeoclimatic cycles, global environmental changes and new glacial periods. Based on geological and geochemical records in the boundary layers produced by six huge Cenozoic bolide-impact events (65, 34, 15, 2.4, 1.1, 0.73 Ma B.P.), including those at 34, 15, 1.1 and 0.73 Ma B. P. which are represented by four famous tektite-strewn fields, the process and mechanics of palaeoclimatic cycles and global environmental catastrophes induced by extraterrestrial impact are discussed in detail. Impact-generated dust, soot and aerosol floating in the stratosphere could result in short-term (<1 year), rapid drop in temperature immediately after impact. Through self-regulation of the Earth’s climate system, the temperature at the surface slowly went up within 100a and maintained stable for a long time at 250K. If there were no other factors leading to the break-down of the newly-established equilibrium, a new glacial pound would be initiated. Estimating from the thickness of δ¹³C and δ¹⁸O anomalies in sediments across the impact boundary layer and deposition rate, the duration of two stages of the palaeoclimate cycle in the form of cold weather—greenhouse effect—normal weather was 10⁴ – 10⁵a, respectively. The conclusion deduced from the above model is supported by palaeotemperature change recorded by oxygen isotope in sediments across the impact boundary layer. The study was granted by the Scientific and Technological Bureau of Resources and Environment, Chinese Academy of Sciences (KZ952-J1-031) and the National Natural Science Foundation of China.     

Cryptotephrochronology of the Eemian and the last interglacial–glacial transition in the North East Atlantic

The Eemian interglacial and the onset of the subsequent glacial period serve as the most recent analogue for the natural operation of the climate system during the current interglacial. Pronounced climatic oscillations occurred during this period, but their nature and pattern are poorly understood due to dating limitations and unknown phase relationships between different regions and archives. Tephrochronology offers considerable potential for precise correlation of disparate palaeoclimatic archives preserving evidence of these rapid climatic transitions through the tracing of common isochronous tephra horizons. We outline the identification of three previously unknown cryptotephra horizons within a marine core from the Rockall Trough, North East Atlantic. This sequence preserves a high‐resolution record of this interval and shard size, geochemical heterogeneity and the co‐variance of shard concentrations with ice‐rafted debris data are utilized to demonstrate that primary airfall was the most likely transport and depositional pathway. The main geochemical populations of these horizons have similar transitional alkali major and trace element compositions, suggesting that they were derived from a common Icelandic source, potentially the Öræfajökull volcanic system. These tephra horizons represent additions to the North Atlantic event stratigraphy for this period and tentative correlations to Icelandic terrestrial deposits are proposed for two horizons.     

青藏公路纳赤台地区融冻褶皱及其古气候意义

昆仑河及其主要支流的Ⅳ—Ⅰ级阶地发育着融冻褶皱,其形成时代为两期:晚更新世末期(距今20725—14041年),全新世中期(距今约3000年)。它际志着本区在晚更新世末期为连续多年冻土区,年平均气候较今低5—6℃;在全新世新冰期时为岛状多年冻土区,年平均气温较今低2.5—3.0℃。     

桂林地区水南洞14～25万年石笋的碳氧同位素记录和古气候重建

通过对桂林水南洞石笋进行高精度的热电离质谱(TIMS－U)测年和碳氧同位素分析,建立了桂林地区245.20 ka BP至147.90 ka BP间的古气候变化时间序列,确定了石笋记录的时段B与时段C分界的年龄为242.5±6.4 ka BP(相当于深海岩芯氧同位素标准曲线时段7与时段8分界的年龄)、时段A与时段B分界的年龄为 192.6±3.9 ka BP(相当于深海岩芯氧同位素标准曲线时段6与时段7分界的年龄)。桂林地区245.20～147.90 ka BP石笋记录的冷暖事件所反映出的古气候变化,大致可分为3个气候变化阶段:(1) 245.2～242.6 ka BP, 相当于深海岩芯氧同位素标准曲线阶段8的末期;(2) 242.5～192.6 ka BP,相当于深海岩芯氧同位素标准曲线时段7;(3)192.6～147.9 ka BP间的倒数第2次冰期, 相当于深海岩芯氧同位素标准曲线时段6的早中期。石笋的TIMS－U测年和碳氧同位素记录揭示,桂林地区245.2～147.9 ka BP的古气候演变历史与深海岩芯时段8末期、时段7和时段6的氧同位素,深海岩芯中记录的孢子花粉组合、CaCO3含量、海平面的升降变化以及与中国北方黄土、古土壤中记录的孢子花粉组合、成壤程度、全铁富集程度、磁化率变化、原生碎屑CaCO3含量和淋溶强度等所揭示的古气候和古季风变化具有极好的对应关系,表明桂林地区中更新世晚期以来的古气候演变既有全球性特征,又有着强烈的区域性特征。     

赣北鄱阳湖地区土塘剖面第四纪红土地球化学特征及古气候意义

赣北鄱阳湖地区土塘剖面发育第四纪红土,自下而上可分为强网纹红土层、弱网纹红土层、微网纹红土层、均质红土层和下蜀黄土层。基于常量元素、粒度分析数据以及前人年代框架,初探土塘剖面化学风化特征及其古气候意义。(1)土塘剖面粒度组分均一,常量元素含量相近,风化淋溶强烈。(2)土塘剖面各地层间化学风化强度存在差异:下蜀黄土层为初期的去Na、Ca阶段;均质红土层为中期的去K阶段;微网纹红土层由去K阶段向去Si阶段过渡;网纹红土层已完全进入晚期去Si阶段。剖面常量元素的相对迁移能力为:Na₂O>MnO₂>CaO>P₂O₅>MgO>K₂O>SiO₂>Al₂O₃>TiO₂>Fe₂O₃。(3)中更新世以来赣北鄱阳湖地区气候总体上由暖湿趋于干冷,期间伴随多个明显的干湿旋回佐证强烈的淋溶与干湿交替作用是网纹红土发育的重要驱动因子。     

准噶尔盆地南缘三叠纪—侏罗纪之交的古气候*

准噶尔盆地南缘的郝家沟剖面三叠系—侏罗系连续发育,是研究三叠系—侏罗系界线及相关地质问题的重要剖面。孢粉分析发现,上三叠统郝家沟组以气候适应范围较宽的裸子植物花粉占优势,而在下侏罗统八道湾组下部主要适应温暖湿润气候的蕨类植物孢子含量明显增高,在组合中常占据优势地位,说明研究区早侏罗世气候比晚三叠世更为潮湿。沉积岩有机碳同位素分析结果显示,在剖面八道湾组下部的δ¹³C值总体低于-24.5‰,形成两次明显的负向偏移,同时采集的丝炭样品的分析结果也证明δ¹³C在八道湾组下部具有明显负向偏移。根据现代湖泊沉积有机质碳同位素与气候关系的研究成果,沉积有机质稳定碳同位素负偏是气候温暖潮湿化的反应,支持了孢粉研究的结果。以上表明,研究区侏罗纪之初的气候比晚三叠世更加炎热潮湿。     

A high-resolution palaeoclimate record for the last 4800 years from lake la Brava,SE pampas plains,Argentina

Climatic changes are reflected in variations of different parameters. Sequences of lake sediments are good sources of this information because they provide continuous and detailed records of palaeoclimatic changes. In order to determine the changes in climate in SE Pampas plain, in this paper we present a series of rock magnetic studies performed on a bottom core collected from Lake La Brava (Argentina).In order to establish lake level variations, we also measure total sulphur, organic and inorganic carbon (TS, TOC and TIC) content, alkaline elements, light and heavy metals and changes in vegetation communities. Five radiocarbon age determinations were made from samples of organic-rich clay and calibrated ages were calculated. The averaged sediment accumulation rate is 1.3 mm/yr and the sequence represents a temporal extent of about 4800 calibrated years before the present (cal. BP).The main aim was to reconstruct the hydrological balance of the lake, the changes in erosional strength and sediment supply within the catchment area since the Middle Holocene, and to explore the extent to which these may be linked to changes in climate and/or human activities. The results of this work and previous studies suggest periodic changes from cooler to warmer and humid conditions. Relationships between submerged and emergent plants are consistent with the behaviour of magnetic susceptibility. TOC changes suggest wet environment during magnetic enhancement. Floods and lower lake level events were identified in detail. Changes in sediment contribution and depositional processes for the last 50 cal. BP are caused by human impact, particularly by the use of natural resources.     

1100万年以来中国北方风尘堆积与古气候变化的周期及驱动因素分析

中国北方连续堆积的晚新生代风成红粘土-黄土,是气候干湿变化的良好地质记录.对第四纪黄土的研究,揭示了中国北方干湿的周期变化,但是中新世以来的古气候变化规律及其驱动机制还不清楚.通过对具有代表性的红粘土-黄土序列的粒度测试,并根据独立的古地磁地层年代控制,建立了我国北方1100万年以来气候变化的时间序列.在此基础上,应用传统谱分析和小波变换的方法,对1100万年以来的干湿变化进行了分析,讨论了11～7.3 Ma,8.0～5.0 Ma,5.3～2.5 Ma,2.5～1.2 Ma和1.2～O Ma期间我国北方和亚洲中部干湿变化的周期,发现在不同时间段分别存在着～20 ka的岁差周期、～40 ka的黄赤交角周期和～100 ka的地球轨道偏心率周期,获得了地球轨道运动变化引起太阳辐射变化驱动晚新生代亚洲内陆干湿变化的新证据.同时,还发现风尘沉积的粒度时间序列存在非轨道周期,可能是轨道周期谐振和时间标尺不确定性造成的.地球轨道运动变化引起的北半球太阳辆射量的变化,从而引起北半球冰期-间冰期旋回、西风带位置移动和亚洲季风强度的共同变化,可能控制着晚新生代我国北方粉尘沉积过程和古气候变化.加强粉尘堆积记录和古气候模拟研究,可深入认识我国北方晚新生代干湿变化的规律和机制.