7.65Ma BP以来天津滨海地区的植被演变特征     

杨吉龙  秦雅飞  胥勤勉  周新郢  胡云壮  杜东  孟利山 《地质学报》2015,89(6):1134-1143

天津东部广泛分布的中新世沉积物为阐释中新世以来的古植被和古气候提供了研究载体,本文依据塘沽区1226m深G2孔的花粉分析结果,结合古地磁等定年手段,重建了天津滨海地区约7.65Ma BP以来的古植被特征。研究显示,区域地貌环境与气候环境共同作用于周边的植被环境。沉积速率与草本花粉组合具有良好的对应关系,研究表明在约6.73~6.43与3.58~3.03 Ma BP沉积速率较大时形成相对较高的河滩高地,其他时期以盐沼和盐碱地为主。由乔木花粉显示的植被历史表明在6.90~7.65Ma BP周边植被为暖温带落叶阔叶林,代表暖湿环境,3.61~6.9 Ma BP为干旱的疏林草原,2.80~3.6lMa BP为针阔叶混交林,较为凉湿,1.28~2.80 Ma BP为暖温带落叶阔叶林的景观,整体上较为暖湿。1.28Ma BP以来,草本与乔木花粉的波动变化,反应了更新世中后期冷暖气候的波动。  相似文献   

福建泉州晚第四纪盆地沉积的孢粉和微体古生物及其古环境意义     

何耀堂 《福建地质》2011,30(3):224-232

福建泉州晚第四纪沉积物中孢粉,晚更新世以气候适应范围较宽的木本植物花粉占优势,适应温暖湿润气候的蕨类植物孢子较少;早全新世二者含量相当;中全新世蕨类植物孢子增多,木本植物花粉退居第二;晚全新世蕨类植物孢子占绝对优势,木本植物花粉相对减少。草本植物花粉浓度始终不高,但随着时代更新,种类增多。区内微体古生物在晚更新世和早全...  相似文献   

近2ka以来东海内陆架泥质区记录的高分辨率古气候演化     

刘升发  石学法  刘焱光  吴永华  乔淑卿  杨刚 《海洋学报》2011,33(3):85-93

通过对位于东海内陆架泥质区中部的MZ02柱样岩芯进行粒度、常量元素、AMS14C分析,获得了粒度和常量元素随时间变化的高分辨率曲线.结果表明,近2 ka以来研究区沉积环境稳定,以沿岸流控制的浅海沉积为主,沉积物中CaO/K2O,MgO/Al2 O3和MnO/Na2 O比值的变化与我国东部气候变化序列具有较好的一致性,证...  相似文献   

晚古生代全球古气候特征及其研究方法   总被引：3，自引：0，他引：3  

何刚  李双应 《安徽地质》2006,16(4):241-246,256

相对第四纪而言,人们对史前全球古气候的研究还比较薄弱,在方法学方面也需要进一步探讨。本文归纳了古气候演变原因,初步总结了全球晚古生代古气候特征,探讨了古气候的研究方法。一方面,可以据此进一步细化对史前古气候的研究,另一方面旨在古为今用,加强区域和全球不同尺度气候环境的预测,趋利避害,更好地服务于人类。  相似文献   

Spatial distribution of climatic conditions from the Middle Eocene to Late Miocene based on palynoflora in Central,Eastern and Western Anatolia     

Mine Sezgül Kayseri-Özer 《Geodinamica Acta》2013,26(1-2):122-157

The continental climatic evolution of Anatolia has been reconstructed quantitatively for the last 45 million years using the coexistence approach. Although there were some regional effects, the Anatolian Cenozoic continental climate record correlated with the European climatic condition and the global oxygen isotope record from marine environments. From middle Eocene to late Miocene, continental warming in Anatolia was pronounced for inferred winter temperature and mean annual temperature as in Europe. Generally, the palaeoclimatic property of Anatolia resembles the European climatic changing and marine temperature changing based on the oxygen isotope record; however, climatic values of the terrestrial area in Anatolia are higher from Lutetian to Aquitanian and these values are lower than European values from Aquitanian to Tortonian. Correspondingly, Cenozoic climatic cooling in Anatolia is directly associated with an increase of seasonality, palaeogeographic position and terrestrial condition. Furthermore, mean annual precipitation values of Anatolia remained relatively stable during the Eocene–Oligocene; however, these values indicated changing throughout middle–late Miocene. Moreover, in this study, decline of abundance and variables for the mangrove and back mangrove palaeocommunities during the last 45 million years is recorded because of the decreasing of humidity, temperature and increasing of terrestrial condition.  相似文献   

Were Ediacaran siliciclastics of South Australia coastal or deep marine?   总被引：1，自引：0，他引：1  

GREGORY J. RETALLACK 《Sedimentology》2012,59(4):1208-1236

The Late Neoproterozoic Ediacara Member of the Rawnsley Quartzite in South Australia has been considered aeolian, fluvial, intertidal and deep marine by various authors. Palaeosols would not be expected for the deep marine interpretation, but some palaeosols should be evident for the aeolian–fluvial–intertidal interpretations, and this is the first study to examine the Ediacara Member at a petrographic and geochemical scale appropriate to recognize potential palaeosols. Recognition of palaeosols and floodplain facies in Neoproterozoic rocks is a challenge because such rocks are too ancient for diagnostic non‐marine fossils such as root traces. The varied thickness of Ediacara Member red siltstones and white sandstones is distinct from laterally persistent overlying and underlying grey shales and limestones with acritarchs, stromatolites and other marine fossils. The sandstones are trough cross‐bedded and fill palaeovalleys. The red siltstones have poorly sorted, highly angular, silt‐size grains characteristic of loess. Particular sandy and silty beds were sampled for detailed petrographic and geochemical studies, because they include desiccation cracks, sand crystals, ice cracks, carbonate nodules and soft‐sediment deformation like those of palaeosols. Chemical and grain‐size variations within these beds reveal surficial clay formation and oxidation from feldspar as in soils. Petrographic studies also revealed surficial disruption of these palaeosols by filamentous structures comparable with microbial ropes of biological soil crusts. This array of palaeosol features may be of use for recognizing palaeosols in other Neoproterozoic siliciclastic sequences.  相似文献   

江汉盆地江陵凹陷南缘古新统沙市组四段含盐岩系沉积特征及其沉积环境意义   总被引：2，自引：0，他引：2       下载免费PDF全文

王春连  刘成林  胡海兵  毛劲松  沈立建  赵海彤 《古地理学报》2012,14(2):165-175

通过钻井岩心观察及室内测试分析等方法,对江汉盆地江陵凹陷南缘古新统沙市组四段含盐岩系的沉积特征进行了研究.该时期研究区盐湖的特点是:成盐多期次、沉积连续、淡化—成化周期性交替,因而成为恢复古气候和古环境的重要研究对象.该区沙市组四段盐层间的层段由非砂岩组成,主要由单层厚度为几毫米至几十厘米、累积厚度达几十厘米至几米的含...  相似文献   

Evidence for an extreme climatic event on Achill Island,Co. Mayo,Ireland around 5200–5100 cal. yr BP     

C. Caseldine  G. Thompson  C. Langdon  D. Hendon 《第四纪科学杂志》2005,20(2):169-178

A range of detailed palaeoenvironmental analyses carried out on a series of three peat profiles from Achill Island, Co. Mayo, western Ireland, reveal evidence for an extreme climatic event, probably a storm or series of storms, around 5200–5100 cal. yr BP that caused the deposition of an extensive layer of silt across blanket peat. This event followed a period of relatively dry climate during which Neolithic communities expanded in the region. There was a subsequent period of continuing dry conditions allowing extensive colonisation of the peat by Pinus before a shift to wetter conditions characteristic of the later Holocene. The extreme climatic event is possibly linked to human abandonment of the area comparable to that observed from the work on the internationally significant Céide Fields in the same region. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

Climate change in lowland Central America during the late deglacial and early Holocene     

Michael B. Hillesheim  David A. Hodell  Barbara W. Leyden  Mark Brenner  Jason H. Curtis  Flavio S. Anselmetti  Daniel Ariztegui  David G. Buck  Thomas P. Guilderson  Michael F. Rosenmeier  Douglas W. Schnurrenberger 《第四纪科学杂志》2005,20(4):363-376

The transition from arid glacial to moist early Holocene conditions represented a profound change in northern lowland Neotropical climate. Here we report a detailed record of changes in moisture availability during the latter part of this transition (～11 250 to 7500 cal. yr BP) inferred from sediment cores retrieved in Lake Petén Itzá, northern Guatemala. Pollen assemblages demonstrate that a mesic forest had been largely established by ～11 250 cal. yr BP, but sediment properties indicate that lake level was more than 35 m below modern stage. From 11 250 to 10 350 cal. yr BP, during the Preboreal period, lithologic changes in sediments from deep‐water cores (>50 m below modern water level) indicate several wet–dry cycles that suggest distinct changes in effective moisture. Four dry events (designated PBE1‐4) occurred centred at 11 200, 10 900, 10 700 and 10 400 cal. yr BP and correlate with similar variability observed in the Cariaco Basin titanium record and glacial meltwater pulses into the Gulf of Mexico. After 10 350 cal. yr BP, multiple sediment proxies suggest a shift to a more persistently moist early Holocene climate. Comparison of results from Lake Petén Itzá with other records from the circum‐Caribbean demonstrates a coherent climate response during the entire span of our record. Furthermore, lowland Neotropical climate during the late deglacial and early Holocene period appears to be tightly linked to climate change in the high‐latitude North Atlantic. We speculate that the observed changes in lowland Neotropical precipitation were related to the intensity of the annual cycle and associated displacements in the mean latitudinal position of the Intertropical Convergence Zone and Azores–Bermuda high‐pressure system. This mechanism operated on millennial‐to‐submillennial timescales and may have responded to changes in solar radiation, glacial meltwater, North Atlantic sea ice, and the Atlantic meridional overturning circulation (MOC). Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

Transient modelling of lacustrine regressions: two case studies from the Andean Altiplano     

Thomas Condom  Anne Coudrain  Alain Dezetter  Daniel Brunstein  Franois Delclaux  Sicart Jean‐Emmanuel 《水文研究》2004,18(13):2395-2408

A model was developed for estimating the delay between a change in climatic conditions and the corresponding fall of water level in large lakes. The input data include: rainfall, temperature, extraterrestrial radiation and astronomical mid‐month daylight hours. The model uses two empirical coefficients for computing the potential evaporation and one parameter for the soil capacity. The case studies are two subcatchments of the Altiplano (196 000 km²), in which the central low points are Lake Titicaca and a salar corresponding to the desiccation of the Tauca palaeolake. During the Holocene, the two catchments experienced a 100 m fall in water level corresponding to a decrease in water surface area of 3586 km² and 55 000 km², respectively. Under modern climatic conditions with a marked rainy season, the model allows simulation of water levels in good agreement with the observations: 3810 m a.s.l. for Lake Titicaca and lack of permanent wide ponds in the southern subcatchment. Simulations were carried out under different climatic conditions that might explain the Holocene fall in water level. Computed results show quite different behaviour for the two subcatchments. For the northern subcatchment, the time required for the 100 m fall in lake‐level ranges between 200 and 2000 years when, compared with the present conditions, (i) the rainfall is decreased by 15% (640 mm/year), or (ii) the temperature is increased by 5·5 °C, or (iii) rainfall is distributed equally over the year. For the southern subcatchment (Tauca palaeolake), the time required for a 100 m decrease in water level ranges between 50 and 100 years. This decrease requires precipitation values lower than 330 mm/year. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献