宁波平原晚第四纪的古气候变化

基于国土资源大调查项目取得的各类实测地质资料,大致查明了宁波平原晚第四纪的沉积物组成及分布特征,建立了沉积剖面结构;采用¹⁴C和热释光测年、有孔虫和孢粉鉴定等方法,划分出岩石地层和生物地层,研究了沉积物的古环境信息,推测本区晚第四纪的气候变化历程为:湿热-温凉干燥-暖干-温凉湿润-温暖-冷干-温热湿润-温暖,其中晚更新世和全新世各发生一次海侵,规模渐次增大;另外,总结出近十多万年以来本区古气候与全球变化相吻合,并且揭示了古气候变化过程及其与海平面升降、海陆变迁密切相关,气候转暖引起海侵,气候变冷发生海退。     

甘肃北山地区早白垩世松柏类植物Podozamites(苏铁杉属)及其古气候意义*

Podozamites(苏铁杉属)为松柏类已灭绝的形态属,是北半球中生代植物群中的重要分子。经鉴定,甘肃北山地区早白垩世早期地层中产出的Podozamites包括Podozamites sp.(苏铁杉未定种)、Podozamites aff. distans(间离苏铁杉相似种)和Podozamites bullus(美丽苏铁杉)3个种。基于Podozamites大化石记录和古地理分布特征,结合中生代古气候分区,对该属的古气候意义进行综合分析。结果表明: 晚三叠世—中侏罗世,Podozamites数量较为丰富,主要集中分布于北半球温暖湿润气候区; 晚侏罗世—早白垩世,随着干热气候带的扩张,Podozamites丰度下降,分布区域也随温热潮湿气候区变迁而发生迁移。推测Podozamites在中生代的古地理分布主要受到温暖潮湿气候带变迁的影响,其更加适宜生存于温暖湿润的气候条件下,可作为温暖湿润气候的指示分子。     

中生代主要植物化石的古气候指示意义

中生代植物群以真蕨纲、苏铁纲、银杏纲、松柏纲为主,另有苔藓类、石松纲、楔叶纲及其他种子植物等。从化石的形态和结构、埋藏特点、分布及与现生类型的对比等方面,概要地分析了中生代植物群常见分子的古气候指示意义。其中,反映温暖潮湿气候或生境的主要有苔藓类,石松纲的Lycopodites和Selaginellites属等,楔叶纲,真蕨纲的单缝孢类、早白垩世的蚌壳蕨科、海金砂科的Ruffordia属、紫萁科及可能相关的小羽片大型的Cladophlebis,银杏纲银杏目的主要类型,松柏纲杉科的Athrotaxoites、Cunninghamia、Cephalotaxopsis、Sequoia等,紫杉科的Taxus、Torreya等,苏铁杉科Ferganiella、Podozamites、Swedenborgia等以及形态属Elatocladus;反映温凉气候的主要有松柏纲的松科和银杏纲的茨康目;适应热带、亚热带气候的包括真蕨类的海金沙科、合囊蕨科、马通蕨科、双扇蕨科、桫椤科、里白科以及中国蕨科的Onychiopsis等,苏铁目和本内苏铁目的主要类型;指示偏干旱型气候的主要有石松纲的Pleuromeia和Isoetites, 真蕨纲的Weichiselia, 本内苏铁目的Otozamites、Zamites、Ptilophyllum等,松柏纲掌鳞杉科的Pseudoflenelopsis、Flenelopsis、 Hirmeriella和可能属于掌鳞杉科的Brachyphyllum和Pagiophyllum,柏科的Cupressinocladus以及买麻藤目的Ephedrites等。     

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.     

Palaeoclimatic Indicators of China's Quaternary Saline Lake Sediments and Hydrochemistry

In this paper the authors classify saline lake sediments into the cold, warm and eurythermal phases, reveal the consistency between the zoning of hydrochemical types of modern saline lake water and climatic zoning and give climatic parameters under the conditions of typical cold phase (mirabilite and natron), warm phase (thenardite) and slightly warm phase (bloedite) saline lake deposition.     

Potential Usage of Remote Sensing Data in Studying the Behaviour of Shore Drift Along Kerala Coast, India

Landsat images were analysed to examine direction, amount and behaviour of long-shore drift and its contribution towards deciding areas vulnerable to coastal erosion and accretion along the coast of Kerala. Two approaches are adopted while utilizing the remote sensing data. Net shore-drift direction is determined firstly by studying various coastal landform indicators and secondly by studying offshore turbidity distribution patterns. Landform indicators study suggest that during the south-west monsoon period, strong southerly currents are eroding protruded sectors and depositing eroded material, though partially, along varying sectors. Whereas during the rest of the year, under the influence of a northerly current, accretion is taking place along retreating sectors which has been reflected in the development of beach ridges. Turbidity pattern distribution exhibited by satellite image suggests that for January and February, long-shore drift is from south to north. The results of the two studies were found to be comparable. It may be concluded that shore-drift direction, which can be determined effectively by remote sensing, is season-dependent and plays a significant role in deciding the areas of coastal erosion and accretion.     

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℃。     

The interpretation of inverse isochron diagrams in Ar/Ar geochronology

The concepts involved in the construction and interpretation of inverse isochron diagrams used in ⁴⁰Ar/³⁹Ar geochronology are reviewed. The diagrams can be useful as a means of recognising atmospheric argon and excess ⁴⁰Ar, incorporated in the mineral lattice, which cannot be recognised from ⁴⁰Ar/³⁹Ar spectra. The age established using an inverse isochron plot, unlike that yielded by a spectrum, is not affected by trapped argon ⁴⁰Ar/³⁶Ar ratios that are different from the atmospheric argon ratio (e.g. due to excess ⁴⁰Ar), and may contribute to a better age interpretation. However, a heterogeneous distribution of excess ⁴⁰Ar or heterogeneous argon loss can cause ‘false’ isochrons, with axial intercepts indicating an incorrect age and an incorrect trapped argon composition. Inconsistency between the ages from a spectrum and from the associated inverse isochron plot may indicate the degree of inaccuracy of isochrons. However, it is possible that both the spectrum and inverse isochron yield the same incorrect age. The importance of considering all possible interpretations before assigning an age to a specimen is stressed.     

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。     

我国晚中生代单缝孢真蕨植物兴衰史及意义

从大化石和孢粉资料两方面总结了我国晚中生代单缝孢类真蕨植物的特点及其兴衰史，认为单缝孢类真蕨植物的在我国北方地区早白垩世植物群中的出现，繁盛和衰退与该地区的潮湿，特别是温暖潮湿型古气候背景关系十分密切，据此阐明了该类植物的潮湿，特别是温暖潮湿型古气候的指示意义，其中多数化石与现生真蕨Ａｔｈｙｒｉｕｍ，Ｄｒｙｏｐｔｅｒｉｓ属等的形态和繁殖器官结构非常相拟，反映真蕨类进入了一个新的演化阶段，并提出Ｄｒ