冰消期以来宣化盆地的植被与环境   总被引：2，自引：0，他引：2  

孙黎明  许清海  阳小兰  梁文栋  孙昭宸 《地质力学学报》2001,7(4):303-308

在河北省宣化盆地黄家堡附近,作者通过对具有放射性碳测年支持的孢粉剖面的研究,揭示了该区14000aBP以来的植被和气候变化。在14000aBP~9000aBP间,宣化盆地是以油松为主的针阔混交林草原景观,海拔较高的山上还有云杉、冷杉组成的暗针叶林生长,推测当时的气候条件温凉湿润;至9000aBP~2400aBP间,宣化盆地的古植被演变成以蒿为主的草原景观,在水分、土壤条件较好的地方生长着由柳、榆、栎、桦等组成的落叶阔叶林,推测当时的气候温和湿润;2400aBP以后,宣化盆地的植被演变成以藜科为主的荒漠化草原景观,气候以凉干为特征。   相似文献   

Late Quaternary speleothem pollen in the British Isles     

Christopher J. Caseldine  Siobhán F. McGarry  Andy Baker  Chris Hawkesworth  Peter L. Smart 《第四纪科学杂志》2008,23(2):193-200

As with many terrestrial areas, the British Quaternary sequence is characterised by incomplete, fragmentary records, whose correlation is based on stratigraphic or biostratigraphic techniques due to the lack of radiometric ages beyond the ～40 kyr limit of ¹⁴C dating. Speleothems (secondary cave calcite deposits) offer a significant advantage over many sources of palaeoenvironmental information; they can be dated to a high precision and accuracy by uranium‐thorium (²³⁸U‐²³⁰Th) thermal ionisation and inductively coupled plasma (ICP) mass spectrometry in the time period back to 500 kyr. They may also contain sufficient well‐preserved pollen representative of contemporary vegetation above the cave to allow palaeoenvironmental reconstruction. This study adopts the novel approach of combining pollen and thermal ionisation mass spectrometric (TIMS) U‐Th dating of British speleothems to produce well‐constrained palaeoenvironmental records. We report for the first time precisely dated records of pollen assemblages from speleothems suggesting the presence of thermophilous arboreal species in phases previously considered to have been consistently cool or cold and devoid of trees. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

Late Quaternary paleolimnology of Walker Lake,Nevada     

J. Platt Bradbury  R. M. Forester  R. S. Thompson 《Journal of Paleolimnology》1988,1(4):249-267

Diatoms, crustaceans, and pollen from sediment cores, in conjunction with dated shoreline tufas provide evidence for lake level and environmental fluctuations of Walker Lake in the late Quaternary. Large and rapid changes of lake chemistry and level apparently resulted from variations in the course and discharge of the Walker River. Paleolimnological evidence suggests that the basin contained a relatively deep and slightly saline to freshwater lake before ca. 30 000 years B.P. During the subsequent drawdown, the Walker River apparently shifted its course and flowed northward into the Carson Sink. As a result, Walker Lake shallowed and became saline. During the full glacial, cooler climates with more effective moisture supported a shallow brine lake in the basin even without the Walker River. As glacial climates waned after 15 000 years ago, Walker Lake became a playa. The Walker River returned to its basin 4700 years ago, filling it with fresh water in a few decades. Thereafter, salinity and depth increased as evaporation concentrated inflowing water, until by 3000 years ago Walker Lake was nearly 90 m deep, according to dated shoreline tufas. Lake levels fluctuated throughout this interval in response to variations in Sierra Nevada precipitation and local evaporation. A drought in the Sierras between 2400 and 2000 years ago reduced Walker Lake to a shallow, brine lake. Climate-controlled refilling of the lake beginning 2000 years ago required about one millennium to bring Walker lake near its historic level.Through time, lake basins in the complex Lake Lahontan system, fill and desiccate in response to climatic, tectonic and geomorphic events. Detailed, multidisciplinary paleolimnologic records from related subbasins are required to separate these processes before lake level history can be reliably used to interpret paleoclimatology.This is the fifth of a series of papers to be published by this journal that was presented in the paleolimnology sessions organized by R. B. Davis and H. Löffler for the XIIth Congress of the International Union for Quaternary Research (INQUA), which took place in Ottawa, Canada in August 1987. Drs. Davis and Löffler are serving as guest editors of this series.  相似文献   

The impact of the Laacher See Tephra on terrestrial and aquatic ecosystems in the Black Forest,southern germany     

A. F. Lotter  H. J. B. Birks 《第四纪科学杂志》1993,8(3):263-276

Late-glacial lake sediments containing the Laacher See Tephra (LST, 11000 yr BP) have been analysed for pollen and diatoms at two sites (Hirschenmoor, Rotmeer) in the montane belt of the Black Forest (southern Germany) in order to detect the possible impact of this major volcanic eruption on terrestrial and aquatic biota. The pollen assemblages at both sites show a minor increase in grasses and sedges following the tephra deposition, whereas the pollen of aquatic macrophytes do not show any consistent pattern. Partial redundancy analysis and Monte Carlo permutation tests suggest, however, that the LST had no statistically significant effect either on the terrestrial or aquatic pollen assemblages at either site when the effects of time and climatic change are allowed for statistically. The diatom assemblages at both sites changed after the deposition of the LST and diatominferred pH estimates suggest a short but non-significant excursion towards lower values. Multivariate analyses of the diatom data indicate a statistically significant impact of the deposition of the LST and associated changes in sediment lithology on the diatom assemblages when the effects of climatic change and time are allowed for statistically. However, owing to the interaction between tephra and lithology it is not possible to conclude if the diatom changes were caused by the deposition of the LST or by lithological changes.  相似文献   

The Würmian Late-glacial in Iowland Switzerland     

B. Ammann  A. F. Lotter  U. Eicher  M.-J. Gaillard  B. Wohlfarth  W. Haeberli  G. Lister  M. Maisch  F. Niessen  Ch. Schlüchter 《第四纪科学杂志》1994,9(2):119-125

A synthesis is provided of Late-glacial (14-9 ka BP) environmental changes in lowland Switzerland (the ‘Swiss Plateau’). The chronology of deglaciation and subsequent developments in vegetation cover in the area are summarised. The sequence of climatic variations experienced in the region during the Late-glacial is then described and a curve representing the main palaeotemperature variations is presented.  相似文献   

European vegetation history: Palaeovegetation maps from pollen data - 13 000 yr BP to present     

Brian Huntley 《第四纪科学杂志》1990,5(2):103-122

Pollen data are the most important source of information with respect to late Quaternary vegetation history. Broad-scale palaeovegetation patterns have been subjectively inferred from mapped pollen data by previous authors. In this study, multivariate classification was applied to European pollen data for the last 13 000 yr. The resulting clusters are mapped at millennial intervals and can be equated with vegetation units. The maps portray the changing vegetation of Europe since the last glacial. They reveal the impermanence of the assemblages of species that ecologists recognise as communities. The dominant patterns in the maps also change through time, indicating important changes in palaeoenvironmental conditions and in the alignment of major environmental gradients. Human impact upon European vegetation history is seen to be relatively unimportant when the vegetation is viewed at a continental scale.  相似文献   

Mid-Holocene Hydrologic Model of the Shingobee Watershed, Minnesota     

Sheryl K. Filby  Sharon M. Locke  Mark A. Person  Thomas C. Winter  Donald O. Rosenberry  John L. Nieber  William J. Gutowski  Emi Ito 《Quaternary Research》2002,58(3):246

A hydrologic model of the Shingobee Watershed in north-central Minnesota was developed to reconstruct mid-Holocene paleo-lake levels for Williams Lake, a surface-water body located in the southern portion of the watershed. Hydrologic parameters for the model were first estimated in a calibration exercise using a 9-yr historical record (1990–1998) of climatic and hydrologic stresses. The model reproduced observed temporal and spatial trends in surface/groundwater levels across the watershed. Mid-Holocene aquifer and lake levels were then reconstructed using two paleoclimatic data sets: CCM1 atmospheric general circulation model output and pollen-transfer functions using sediment core data from Williams Lake.Calculated paleo-lake levels based on pollen-derived paleoclimatic reconstructions indicated a 3.5-m drop in simulated lake levels and were in good agreement with the position of mid-Holocene beach sands observed in a Williams Lake sediment core transect. However, calculated paleolake levels based on CCM1 climate forcing produced only a 0.05-m drop in lake levels. We found that decreases in winter precipitation rather than temperature increases had the largest effect on simulated mid-Holocene lake levels. The study illustrates how watershed models can be used to critically evaluate paleoclimatic reconstructions by integrating geologic, climatic, limnologic, and hydrogeologic data sets.  相似文献   

赤峰地区孢粉分析与先人生活环境初探   总被引：15，自引：5，他引：15  

许清海  杨振京  崔之久  阳小兰  梁文栋 《地理科学》2002,22(4):453-457

从考古孢粉学角度，根据赤峰七锅山剖面孢粉分析，结合赤峰地区古文化遗址的考古资料，探讨了赤峰地区8000aB.P.以来的先人生活环境，以及人类活动和自然环境演变的过程之间的相互关系，结果表明：8400－6200aB.P. 为温暖湿润的草原气候，先人既狩猎捕鱼，也种植作物和放牧；6200－4000aB.P,，随着森林的破坏，环境逐渐恶劣，农业水平下降；4000－2500aB.P.植被以草原为主，气候温干，先人以旱作农业为主，2500aB.P.至现在，植被为典型的蒿草草原，气候温和偏干，农业和畜牧业相对发展，人类活动加剧。  相似文献   

江苏海州湾海区表层沉积物的孢粉研究     

肖霞云  萧家仪  陈晔 《地理与地理信息科学》2002,18(1):83-86

对江苏海州湾近岸海区的表层沉积物进行孢粉分析 ,总结该研究区的孢粉分布规律及成因。笔者认为该区的松花粉主要来自西北部胶东半岛 ;落叶阔叶乔木花粉来源于连云港市云台山 ;草本植物花粉与陆缘植被相应 ,以盐生的蒿、藜科花粉占优势 ,表明花粉沉积与当地及周边地区植被密切相关。蕨类孢子是从陆地由水流携带搬运而来 ,百分含量的高低可能是受补偿率的影响。  相似文献   

北亚热带江淮地区白浆化土壤的发生学特性     

傅桦  丁瑞兴 《地理研究》2001,20(4):431-438

通过孢子花粉、石英砂颗粒和土壤微形态学分析,研究北亚热带江淮地区白浆化土壤的发生学特性。白浆化土壤下部土体经历了暖温带森林草原景观和亚热带草原景观,为高能化学环境。在母质沉积后,经历了褐土化过程或其他物质堆积,经过一定时期的沉积间断后,堆积新物质,随着气候的变化,成土环境演变为现代气候类型,属亚热带森林草原环境。淀积层也源于黄土状物质,风化程度更强,白浆层则为后期堆积物,不具备高能化学环境。淀积层在高能环境下,存在次生粘化和淀积粘化作用。  相似文献