Recent sedimentation in a high arctic lake, northern Ellesmere Island, Canada     

Bern Zolitschka 《Journal of Paleolimnology》1996,16(2):169-186

A multiple core study was conducted on laminated minerogenic sediments from Lake C2, Northern Ellesmere Island, Canadian High Arctic. Lateral persistence, distal thinning, variation in grain size of these laminations as well as present-day processes of highly seasonal sediment transfer into the lake basin suggest that clastic varves have been formed. Sedimentation rates based on ²¹⁰Pb dating agree well with sedimentation rates based on lamination counts giving further evidence that laminations are annual. Errors in varve counting were reduced from 12% to < 2% using the multi-core approach of cross-correlating all records. Varved sediments are occasionally interrupted by thick coarse-grained layers, which are interpreted as deposits of turbidity currents and may be related to extremely high discharge events and slope failures of the delta front. Micro-laminated sediments spanning the last two centuries were studied in detail. Suspension settling is the dominant process of deposition depending upon stream discharge which is controlled by nival melt and summer temperatures. Application of varve chronology thus allows to use lamination thickness measurements as source of high resolution proxy data for palaeoclimatic reconstruction.This is the fifth in a series of papers published in this issue on the Taconite Inlet Lakes Project. These papers were collected by Dr R. S. Bradley.  相似文献   

Mid-holocene climate change in Lake Bosumtwi, Ghana     

James Russell  Michael R TalbotBrian J Haskell 《Quaternary Research》2003,60(2):133-141

Lake Bosumtwi is one of the most widely studied palaeoclimate archives in West Africa. Results from numerous AMS ¹⁴C dates of samples from four piston cores from Lake Bosumtwi show that an abrupt sedimentary transition from a mid-Holocene sapropel to calcareous laminated muds occurred at about 3200 cal yr B.P. High-resolution analyses of the nitrogen isotopic composition of organic matter across this transition confirm its abrupt nature, and suggest that the change may signal a step toward increased aridity and intensified surface winds that affected western equatorial Africa from Ghana to the Congo basin. Northern and Eastern Africa experienced a similar abrupt shift toward aridity during the late Holocene, but at about 5000 cal yr B.P., a difference in timing that illustrates the regional nature of climate changes during the Holocene and the importance of feedback mechanisms in regulating Holocene climate variability. Furthermore, an abrupt change at about 3000 cal yr B.P. occurs at several sites adjacent to the tropical and subtropical Atlantic, which may hint at major changes in the surface temperatures of the tropical Atlantic and/or Pacific at this time.  相似文献   

中国石炭纪古生物地理与古气候   总被引：2，自引：0，他引：2  

王治平  杨逢清 《地球科学》1988,(5)

本文从分析沉积及生物群出发,结合世界构造古地理和气候分带,将中国早石炭古生物地理分属三个生物区,即华夏生物区,中蒙海生物区和东冈瓦纳生物区。晚石炭世的生物分区与早石炭世大体相似。中国早石炭世的古气候分为华夏热带—亚热带区,准噶尔—兴安北温带区和西藏南部南温带区。其界线大致与古生物地理分区相合。晚石炭世中国气候分带与早石炭世相似。  相似文献   

Periodicities in natural remanent magnetization and palaeoclimatic records detected by walsh spectra     

J. G. Negi  R. K. Tiwari 《Pure and Applied Geophysics》1990,132(4):757-769

The time series consisting of nonsinusoidal Natural Remanent Magnetization (NRM) and palaeoclimatic variations for the past two million years have been spectrally examined by using a new Walsh transform technique. The results show statistically significant periodicities (at 95% confidence level) of approximately 92,000 years; 43,000 years and 21,000 years in the ensemble spectra of the NRM intensity (mineralogic) variations. These NRM periodicities are remarkably close to the well-known Milankovitch cycles. The ensemble spectra of palaeoclimatic records reveal only 41,000 years statistically significant (95%) periodicity corresponding to the obliquity cycle. The study suggests that NRM variations in deep sea sediments probably are more sensitive recorders of palaeoclimatic memory than the oxygen isotope variations.  相似文献   

青藏高原北部新生代湖相碳酸盐岩碳氧同位素特征及古环境意义   总被引：3，自引：2，他引：3  

伊海生  林金辉  周恳恳  李军鹏 《古地理学报》2007,9(3):303-312

对青藏高原北部地区新生代陆相地层中湖相碳酸盐岩进行了系统采样分析，以碳氧同位素作为古环境和古气候变化的替代指标,试图从古湖泊演化的角度，阐明高原新生代早期环境演变历史和过程。研究结果表明，该区所有分析样品中生物碎屑灰岩类样品的δ¹⁸O和δ¹³C显示最低值，反映它们沉积在一个水体滞留时间短的开放性淡水湖泊系统中。泥晶灰岩类样品的δ¹⁸O和δ¹³C之间具有正相关关系，表明它们发育在蒸发作用明显的封闭性咸水湖泊体系中，而叠层石灰岩类明显富集13C可能与微生物活动有关。从始新世到渐新世至中新世，湖相碳酸盐岩δ¹⁸O值具有逐渐增大的趋势，δ¹³C则由古近纪的负值变为新近纪的正值，反映该区古湖泊系统经历了一个由开放到封闭的过程，预示古近纪到新近纪之交高原古气候格局发生了重大变革。  相似文献   

黑龙江鸡东盆地中中新世湖盆演变和植被变化研究     

舒军武  王伟铭  尹德顺  王金山 《地层学杂志》2007,31(3):247-254

黑龙江鸡东盆地是受古、新近纪敦密断裂带作用而形成的断陷含煤盆地。依据该盆地91-205钻孔永庆组的岩性变化特点和盆地构造演化阶段,识别和阐述了中中新世湖盆发育的3个阶段,即早期湖泊形成发展阶段、中期湖泊扩张最大阶段和晚期湖泊收缩衰退阶段,并揭示湖泊阶段性发展的旋回性特征。根据孢粉资料,恢复湖盆各个不同发育阶段的古植被面貌,重建当时的古气候。结果表明植被经历了北亚热带含常绿阔叶成分的落叶阔叶林、暖温带—北亚热带落叶阔叶林以及含亚高山针叶树种的暖温带—北亚热带落叶阔叶林阶段,鸡东盆地中中新世湖泊的演变和植被更替存在着潜在的关联。  相似文献   

西藏阿里札达盆地上新世-早更新世的古植被、古环境与古气候演化   总被引：5，自引：0，他引：5       下载免费PDF全文

朱大岗  孟宪刚  邵兆刚  杨朝斌  韩建恩  余佳  孟庆伟  吕荣平 《地质学报》2007,81(3):295-306

本文将西藏札达盆地河湖相地层重新划分为第四系下更新统香孜组(Qp1-1x)、新近系上新统古格组(N22g)和上新统托林组(N21t)。河湖相地层的古地磁法和ESR法测年结果表明,札达盆地内河湖相沉积地层的形成时代为新近纪上新世—第四纪早更新世。根据该套河湖相地层沉积演化和其中的孢粉组合特征、河湖相沉积中所发现的各种古动植物化石等的综合分析,笔者对札达盆地上新世—早更新世的古植被、古环境与古气候演变进行了探讨。结果表明,札达地区上新世—早更新世气候经历了从湿热—温暖潮湿—偏冷潮湿—寒冷干旱的变化,以及植被从森林—灌木—草原的逐渐演化。可将札达盆地上新世—早更新世环境演化划分为7个大的阶段,其总体特征是15.4~4.4Ma,札达地区处于亚热带湿热气候环境;24.4~3.95Ma,为暖温带温暖潮湿气候;33.95~3.5Ma,为偏凉潮湿阶段,气候开始转冷;43.5~3.2Ma,为温暖潮湿阶段;53.2~2.9Ma,气候转为偏冷潮湿阶段;62.9~2.57Ma,该阶段气候偏冷而干旱,整体较为干冷;72.57~1.36Ma,气候寒冷而干旱。表明自上新世—早更新世,该区的古气候环境在逐渐变干、变冷的总趋势上,经历了多次明显的冷暖与干湿波动。  相似文献   

An expanded surface-water palaeotemperature inference model for use with fossil midges from eastern Canada   总被引：4，自引：0，他引：4  

Ian R. Walker  André J. Levesque  Les C. Cwynar  André F. Lotter 《Journal of Paleolimnology》1997,18(2):165-178

Using an expanded surface sample data set, representing lakes distributed across a transect from southernmost Canada to the Canadian High Arctic, a revised midge-palaeotemperature inference model was developed for eastern Canada. Modelling trials with weighted averaging (with classical and inverse deshrinking; with and without tolerance downweighting) and weighted averaging partial least squares (WA-PLS) regression, with and without square-root transformation of the species data, were used to identify the best model. Comparison of measured and predicted temperatures revealed that a 2 component WA-PLS model for square-root transformed percentage species data provided the model with the highest explained variance (r =0.88) and the lowest error estimate (RMSEP _jack =2.26 °C). Comparison of temperature inferences based on the new and old models indicates that the original model may have seriously under-estimated the magnitude of late-glacial temperature oscillations in Atlantic Canada. The new inferences suggest that summer surface water temperatures in Splan Pond, New Brunswick were approximately 10 to 12 °C immediately following deglaciation and during the Younger Dryas. During the Allerod and early Holocene, surface water temperatures of 20 to 24 °C were attained. The new model thus provides the basis for more accurate palaeotemperature reconstructions throughout easternmost Canada.  相似文献   

用黄土地球化学参数进行古气候定量估算的初步尝试   总被引：7，自引：1，他引：6  

孙继敏  刁桂仪 《地球化学》1999,28(3):265-272

尝试了用表土地球化学转换函数恢复渭南剖面最近１３万ａ米的古温度,古降水。结果显示：（１）全新世适宜期及末次间冰期时,降水量显著增加,渭南地区的年降水量可大于７００ｍｍ（２）末次冰期时降水量明显低于全新世适宜期及末次间冰期,但是这一时期有一些次一级的变化;特别与深海Ｏ同位素阶段４对应的时期不仅降水量显著降低,而且还有更次一级的变化;（３０全新世适宜期时,渭南地区的年平均温度在１２－１４℃左右,末次冰  相似文献   

Palaeoclimatic studies in South Shetland Islands,Antarctica, based on numerous stratigraphic variables in lake sediments     

Svante Björck  Hannelore Håkansson  Siv Olsson  Lena Barnekow  Jan Janssens 《Journal of Paleolimnology》1993,8(3):233-272

The hitherto longest found lake sediment sequence on Byers Peninsula, Livingston Island, South Shetland Islands, was analysed with respect to lithology, chronology, diatoms, Pediastrum, pollen and spores, mosses, mineralogy, and sediment chemistry. During the ca. 5000 year long development the sediments were influenced by frequent tephra fall-outs. This volcanic impact played a major role in the lake's history during two periods, 4700–4600 and 2800–2500 BP, but was of importance during the lake's entire history with considerable influence on many of the palaeoenvironmentally significant indicators. The large and complex data set was analysed and zonated with different types of multivariate analysis. This resulted in a subdivision of the sequence into 8 time periods and 21 variables. Redundancy analysis (RDA) of this data set, both without and with the tephra periods, and with 4–6 of the variables as explanatory environmental variables, reveal that climatic/environmental signals are detectable. The palaeoclimatic picture that emerged out of the tephra noise suggests that the first 100 years were characterized by mild, humid conditions. This was followed by a less mild and humid climate until ca. 4000 BP when a gradual warming seems to have started, coupled with increased humidity. These mild and humid conditions seem to have reached an optimum slightly after 3000 BP. At ca. 2500 BP a distinct climatic deterioration occurred with colder and drier conditions and long seasons with ice cover. This arid, cold phase probably reached its optimum conditions at ca. 1500 BP, when slightly warmer conditions might have prevailed for a while. Except for the modern sample with rather mild climate, the last 1400 years seem to have been fairly arid and cold, and the effects of the frequent volcanic activity during this period is only vaguely seen in the records.  相似文献