Fish Remains from Homestead Cave and Lake Levels of the Past 13,000 Years in the Bonneville Basin     

Jack M. Broughton  David B. Madsen  Jay Quade 《Quaternary Research》2000,53(3):392

A late Quaternary ichthyofauna from Homestead Cave, Utah, provides a new source of information on lake history in the Bonneville basin. The fish, represented by 11 freshwater species, were accumulated between 11,200 and 1000 ¹⁴C yr B.P. by scavenging owls. The ⁸⁷Sr/⁸⁶Sr ratio of Lake Bonneville varied with its elevation; ⁸⁷Sr/⁸⁶Sr values of fish from the lowest stratum of the cave suggest they grew in a lake near the terminal Pleistocene Gilbert shoreline. In the lowest deposits, a decrease in fish size and an increase in species tolerant of higher salinities or temperatures suggest multiple die-offs associated with declining lake levels. An initial, catastrophic, post-Provo die-off occurred at 11,300–11,200 ¹⁴C yr B.P. and was followed by at least one rebound or recolonization of fish populations, but fish were gone from Lake Bonneville sometime before 10,400 ¹⁴C yr B.P. This evidence is inconsistent with previous inferences of a near desiccation of Lake Bonneville between 13,000 and 12,000 ¹⁴C yr B.P. Peaks in Gila atraria frequencies in the upper strata suggest the Great Salt Lake had highstands at 3400 and 1000 ¹⁴C yr B.P.  相似文献   

鄂西地区早期人类和巨猿生存环境研究     

程捷  郑绍华  高振纪  张兆群  冯晓波  王晓宁 《地质学报》2006,80(4):473-480

本文重点研究了湖北建始高坪龙骨洞早期人类和巨猿生存时期的气候和环境。通过孢粉、氧化物、磁化率、哺乳动物化石研究表明,高坪地区在早更新世早期气候比较温暖湿润,但存在较大幅度的波动,植被为针叶-阔叶混交林。古人类生存时的气温比现今高,但降雨量比现今少,而且在1.95~2.14MaBP和2.15MaBP发生两次比较明显的降温事件,降温幅度可达5~9℃。  相似文献   

中更新世气候转型时期南海生态环境的南北差异   总被引：2，自引：0，他引：2  

李前裕  汪品先  陈木宏  郑范  王汝建  孙湘君  刘传联  成鑫荣  翦知湣 《地球科学进展》2006,21(8):781-792

中更新世气候转型在南海浮游有孔虫、氧同位素和其它生物记录上主要反映在900 ka BP前后发生高频率变化，特别是指示表层水骤然降温。北部冬季表层水温从24~25℃降至17~28℃，而南部也从26~27℃降至23~24℃。总的降温趋势与开放西太平洋一致，直接反映了西太平洋暖池在900 ka BP之后MIS22期间有明显的减弱。表层水大幅度降温还发生在后继的MIS 20、18、16几大冰期，说明主要冰期旋回周期由41 ka转变为100 ka经历了长达400 ka的过渡时期，并且冬季风增强也在过渡时期的后半段最明显。南海南北生物组合和δ18O值的差异，突出了中更新世气候转型期边缘海区南北气候梯度反差和冬季风在冰期增强的讯号。结论是：生态环境系统反应总体表现与冰期旋回一致的同时，还包含了独特的地区性系统演变特征。但是，南海—西太平洋地区在0.9 Ma BP前后表层海水盐度因东亚冬季风和海平面下降的定量变化，以及这些变化对气候转型时期海—气耦合过程和生态环境系统的影响，尚缺乏足够的资料和证据。  相似文献   

青藏高原多期次隆升的环境效应   总被引：28，自引：0，他引：28  

葛肖虹  任收麦  马立祥  吴光大  刘永江  袁四化 《地学前缘》2006,13(6):118-130

青藏高原隆升对中国西部环境变迁起着决定性影响。通过对柴达木、吐鲁番—哈密、塔里木盆地的演化及其与青藏高原隆升的耦合研究,以柴达木盆地为时空坐标,认为高原隆升可分为三大阶段:(1)古近纪期间青藏高原隆升仅限于冈底斯山一带。当时,受行星纬向气候带控制,中国西北地区为干旱亚热带草原和热带雨林环境,大面积准平原化、泛盆地化,在构造上处于伸展-夷平的拉张环境,与现今亚洲大陆东部相似;(2)青藏高原整体的初次隆升发生在中新世早—中期(23~11·7Ma)。因青藏高原和大兴安岭的阻隔,古近纪的纬向气候带逐渐转变为中亚季候风,古黄土(22Ma)、三趾马动物群的发育,说明高原北缘当时为干旱的荒漠草原环境。同时,这次隆升引起中—晚中新世中国西部广袤地域古地形-构造面貌的变化;(3)形成现今高原面貌的末次快速隆升发生在0·9~0·8Ma。早更新世晚期,印度洋快速扩张,印度板块向中亚大陆脉冲式(A型)陆内俯冲,使得高原快速挤压隆升。这次隆升不仅使高原本身的环境骤变,出现第四纪以来最大的冰川,形成世界上最大的高寒草原,而且引起了全球气候的变化,促使北极圈冰盖的形成。同时,高原隆升使高原内部和周边出现强烈的挤压构造变形,如柴达木、河西走廊、塔里木、吐鲁番—哈密、准噶尔等诸盆地内几万米厚度中—新生界的构造变形与昆仑山、祁连山、天山、阿尔泰山的挤出式双向推覆隆升,形成了中国西北的盆-山地貌。现今,随着青藏高原的持续隆升,高寒草原开始退化,造成中国西北地区大面积的荒漠化,成为制约我国西部生态环境的重要因素。  相似文献   

Age model, physical properties and paleoceanographic implications of the middle Pleistocene core sediments in the Choshi area, central Japan     

Koji  Kameo  Makoto  Okada  Moamen  El-Masry  Toshio  Hisamitsu  Saneatsu  Saito  Hiroomi  Nakazato  Naohiko  Ohkouchi  Minoru  Ikehara  Hisato  Yasuda  Hiroshi  Kitazato  Asahiko  Taira 《Island Arc》2006,15(3):366-377

Abstract   A continuous, well-preserved core was obtained from the Choshi area, on the Pacific side of Japan, to investigate paleoceanographic and paleoclimatic changes around the northwestern Pacific region during the middle Pleistocene. Siliciclastic sequences in the core are divided into five formations – the Obama, Yokone, Kurahashi and Toyosato Formations in the Inubo Group and the Katori Formation, in ascending order. Examination of calcareous nannofossils and magnetic polarities detected four datums in the core sediments of the Inubo Group: the top of Reticulofenestra asanoi , the base of Helicosphaera inversa , the top of Pseudoemiliania lacunosa and the Brunhes–Matuyama boundary. Fourteen marine isotope stages (MIS24–MIS11) were identified in the δ¹⁸O and δ¹³C records based on detected datums and the graphic correlation with the standard stack oxygen isotope curve. Magnetic susceptibility and gamma-ray attenuation porosity evaluator density were also measured and low values characterize the glacial intervals. Biogenic sedimentation by primary production may be larger during the glacial periods because of invasions of nutrient-rich northern surface-waters related to the southward shift of the Kuroshio front in the Choshi area.  相似文献   

黄河源区早更新世含植物化石地层的发现及意义   总被引：1，自引：0，他引：1       下载免费PDF全文

张森琦  王永贵辛元红赵 越李永国王占昌石维栋尚小刚 《中国地质》2006,33(1):78-85

通过对扎根加陇早更新世湖相地层(1919.6kaB.P.)、棒咯涌K5号钻孔早更新世河湖相地层(1135.9～945.4kaB.P.)、野牛河西岸早更新世河湖相地层(1548.2～765.4kaB.P.)以及产于扎根加陇早更新世湖相地层中的植物化石、各剖面孢粉资料的分析,获知黄河源区早更新世早期为亚热带山地针叶林植被景观,地层中木本植物花粉占绝对优势,以针叶植物云杉属、松属、冷杉属、铁杉属为主,是源区动植物发育的鼎盛时期;进入早更新世晚期初,乔木植物花粉迅速减少乃至全部消失,草本植物花粉大幅度增加。晚期末,孢粉出现贫化,以草本植物花粉为主,呈现荒漠草原植被景观。提出了现今黄河源区生态地质环境的形成是地质演化的必然结果。  相似文献   

西藏阿里札达盆地早更新世早期沉积及其古气候与古环境变化          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 《中国地质》2006,33(6):1276-1284

综合分析了西藏阿里札达盆地早更新世早期的多种与气候环境变化密切相关的地质记录，结果表明该区早更新世早期的沉积可划分为3种不同的沉积相和4个岩性段；古气候与古环境变化可划分为4个阶段：（1）2．68-2．45Ma。为冲洪积相沉积。冻融褶皱开始出现，植被以乔木为主，主要为松、藜、蒿，属山地寒温气候；（2）2．45-2．11Ma，为冲洪积相，地层中冻融褶皱多呈扭曲状，草本植物迅速上升，显示出灌木草原气候特征，气候变得凉爽干燥；（3）2．11-1．49Ma，沉积相为冲洪积相-冰缘沉积相，以冰缘沉积相为主，冻融褶皱层开始增多，出现了喜凉的介形类化石。草本植物数量和种类达到最大，灌木也相对增加，显示气候进一步趋于干旱；（4）1．49-1．36Ma，为冰湖沉积相。地层中普遍出现冻融褶皱，喜凉的介形类化石丰度很高，草本植物有小幅下降，但蕨类植物增加幅度较大，显示了干冷草原气候特征。气候干旱寒冷。  相似文献   

Age-estimate evidence for Middle-Late Pleistocene aggradation of River Nene 1st Terrace deposits at Whittlesey, eastern England     

H.E. Langford  K.E.H. Penkman  R.M. Briant  D.H. Keen 《Proceedings of the Geologists' Association. Geologists' Association》2007,118(3):283-300

  相似文献   

Early Pleistocene climate changes in the central Mediterranean region as inferred from integrated pollen and planktonic foraminiferal stable isotope analyses     

Sébastien Joannin  Frédéric Quillévéré  Christophe Lécuyer  François Martineau 《Quaternary Research》2007,67(2):264-274

Vegetation inherited from a Pliocene subtropical climate evolved through obliquity oscillations and global cooling leading to modern conditions. An integrated, highly time-resolved record of pollen and stable isotopes (δ¹⁸O and δ¹³C of Globigerina bulloides) was obtained to understand vegetation responses to Early Pleistocene climate changes. Continental and marine responses are compared in the Central Mediterranean region with a particular consideration of environmental changes during anoxic events.Pollen data illustrate vegetation dynamics as follows: [1] development of mesothermic elements (warm and humid conditions); [2] expansion of mid- and high-altitude elements (cooler but still humid conditions); and [3] strengthening of steppe and herb elements (cooler and dry conditions). These successions correlate with precession. δ¹⁸O variations recorded by Globigerina bulloides define two cycles (MIS 43-40) related to obliquity. At northern low- to mid-latitudes, the pollen signal records temperature and wetness changes related to precession even during global climate changes induced by obliquity. This may result in unexpected increasing wetness during glacial periods, which has to be considered specific to the Central and Eastern Mediterranean region. Lastly, an analysis of anoxic events reveals that enhanced runoff is indicated by increasing frequency of the riparian trees Liquidambar and Zelkova.  相似文献   

Paleoenvironmental analysis of a middle Wisconsinan biota site, southwestern Virginia, U.S.A.     

G. Richard Whittecar  Thomas C. Wynn  Charles S. Bartlett Jr. 《Quaternary Research》2007,68(1):133-140

The Ratcliff Site in southwestern Virginia lies in a small second-order stream valley filled with approximately 3.5 m of organic-rich deposits that contain bones of mammoth, mastodon, deer (or antelope), logs, and plant macrofossils. Radiocarbon analyses indicate the age of the organic-rich sediment ranges from > 44,000 to 29,100 ¹⁴C yr BP, a time period with no fossil remains reported in this region of the Appalachians. Analyses of field observations, textural data, organic carbon content, and plant macrofossils indicate that the organic-rich sediments contain interbedded standing-water and debris-flow deposits. Up to 6 m of oxidized debris-flow sediments bury the organic-rich sediments. The presence of Rubus parviflorus (Thimble Berry) throughout the deposit indicates the site had a boreal environment from > 44,000 to 29,100 ¹⁴C yr BP. Plant macrofossil evidence indicates the uplands had stands of spruce/jack-pine forests while the valley contained ponds and associated wetlands. Three debris flows occurred at the site between approximately 38,000 and 29,000 ¹⁴C yr BP, suggesting a recurrence interval for major storms of approximately 3000 yr, even though the apparent stability of the boreal environment implies a climate not conducive to catastrophic rainstorms. This conflicting combination of features suggests that during the middle Wisconsinan this area experienced generally cool climates, dominated by polar air masses, but was punctuated by relatively brief warm periods marked by incursions of tropical air masses.  相似文献