排序方式: 共有48条查询结果,搜索用时 672 毫秒
31.
青藏高原昆仑山垭口盆地晚上新世以来沉积物磁化率与气候变化 总被引:1,自引:0,他引:1
通过对青藏高原昆仑山垭口盆地磁化率、频率磁化率环境代用指标的分析,并与黄土—古土壤和深海δ18O记录的气候变化进行对比,结合剖面的岩性特征和年代序列以及前人所获得的粒度和孢粉资料,揭示了3.6~0.5 Ma期间昆仑山垭口盆地气候变化经历了六个阶段:3.6~2.48 Ma气候相对冷干、2.48~2.14 Ma气候偏凉湿、2.14~2.07 Ma气候相对冷干、2.07~1.16 Ma气候总体相对较湿润(其间有数次冷干波动)、1.16~0.78 Ma气候偏冷干以及0.78~0.5 Ma气候向冷湿发展。 相似文献
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湘东北燕山晚期花岗岩构造环境判别 总被引:7,自引:0,他引:7
在湘东北中生代多期陆内花岗岩浆活动中 ,燕山晚期花岗岩占有重要地位 ,燕山晚期大规模花岗岩侵入代表一种特殊的构造环境。本文通过湘东北主要燕山晚期花岗岩的岩石化学和微量元素来判别成岩构造环境 ,认为该期花岗岩属于富碱质的钙碱性花岗岩 ,为陆内拉张环境下的产物 ,进一步进行构造环境分类 ,判别其属于后造山PA型花岗岩 ,形成于造山作用后期的拉张环境 ,与陆内裂谷长期拉张的构造环境明显不同。在区域构造演化分析的基础上 ,提出湘东北燕山晚期花岗岩形成于印支—燕山早期陆内挤压 走滑剪切造山作用后期的构造松弛阶段拉张环境 ,燕山晚期PA型花岗岩的出现标志着陆内活化由挤压向拉张的构造转折 ,同时也反映湘东北的陆内活化至少经历了陆内挤压和陆内拉张两个演化阶段。 相似文献
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Data on 2058 late CVS cases, i.e., placental biopsies after 12 completed weeks of pregnancy, were collected from 24 centres. Two major groups of indications with or without ultrasound findings suspicious of fetal chromosomal abnormalities can be differentiated. In the first group, the rates of cytogenetic anomalies (21 per cent) and fetal losses (10 per cent) are high. The respective figures for the low-risk group are 6 per cent for chromosome anomalies and 2 per cent for total fetal losses. To evaluate this rapidly spreading new method further, more data are required and will be collected by the CVS registry based in Philadelphia, U.S.A. 相似文献
35.
de Bonis L Peigné S Likius A Mackaye HT Vignaud P Brunet M 《Die Naturwissenschaften》2007,94(7):575-580
We report on the oldest fox (Canidae) ever found in Africa. It is dated to 7 Ma based on the degree of evolution of the whole
fauna. It belongs to a new species. Its overall size and some morphological characteristics distinguish the Chadian specimen
from all the other foxes. The presence of Vulpes and of the genus Eucyon in slightly younger African locality, as well as in southwestern Europe in the late Miocene, may indicate that canids migrated
in Europe from Africa through a trans-Mediterranean route. 相似文献
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Arzarello M Marcolini F Pavia G Pavia M Petronio C Petrucci M Rook L Sardella R 《Die Naturwissenschaften》2007,94(2):107-112
Some flint lithic artifacts were discovered in the fissure fillings of the well-known Pirro Nord site (Apulia, Southern Italy).
The lithic industry, composed by three cores and some flakes, has been found to be associated to an Early Pleistocene vertebrate
fossil assemblage. The fossil association contains a wide range of micromammals, including Allophaiomys ruffoi and Episoriculus gibberodon and large mammals including Bison degiulii and Equus altidens together with African elements as the gelada baboon Theropithecus and the saber-toothed cat Megantereon whitei. It defines the latest Villafranchian chronological unit (Pirro Nord Faunal Unit) in the Western European mammal biochronology.
The lithic industry of Pirro Nord represents the oldest occurrence of the genus Homo in Europe as it is attributable to a chronological interval between 1.3 and 1.7 Ma. This supports the hypothesis that the
genus Homo, with Oldowaian technology, extended its range in Europe, probably from western Asia, during the first half of the Early
Pleistocene. The new discovery from Pirro Nord changes the chronology of the first arrival of hominids in Europe and offers
new perspectives in the debate about the human dispersal in the Early Pleistocene. 相似文献
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Soizic Le Fur Emmanuel Fara Hassane Taïsso Mackaye Patrick Vignaud Michel Brunet 《Die Naturwissenschaften》2009,96(5):565-574
Characterizing the paleoenvironmental context of the first hominids is a key issue for understanding their behavioral and
morphological evolution. The present study aims at reconstructing the paleoenvironment of the TM266 vertebrate assemblage
(Toros-Menalla, Northern Chad) that yielded the earliest known hominid Sahelanthropus tchadensis (7 Ma). For the first time, a quantitative analysis is carried out on the fossil mammal assemblage associated with that hominid.
Two complementary approaches were applied: (1) the analysis of the relative abundances of taxa and their habitat preferences;
and (2) the study of the distribution of taxa within three meaningful ecovariables: locomotion, feeding preferences, and body
mass. The resulting taxonomic and paleoecological structures are used to reconstruct the diversity and the relative extent
of the habitats in that part of northern Chad seven million years ago. The paleoenvironment was composed of open areas with
dry and humid grasslands, prevailing over wooded habitats. Water was also widely available as freshwater bodies and certainly
swamps. It appears that the high habitat diversity of the landscape is a common feature among paleoenvironments associated
with early hominids. 相似文献
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Pentachlorophenol(PCP) is a widespread,persistent environmental contaminant,and it is enzymatically activated to form a reactive metabolite,tetrachloro-l,4-benzoquinone(TCBQ).To our knowledge,there is no information about TCBQ toxicity on embryonic stem cells.Here,we demonstrated that TCBQ induced significantly apoptosis of mouse embryonic stem cells in a concentration-dependent manner.We also showed that TCBQ elevated genomic5-hydroxymethylcytosine(5hmC) by affecting ten-eleven translocation(Tet) dioxygenases in mouse embryonic stem cells.We further investigated whether Tet dioxygenases were implicated in TCBQ-induced apoptosis.By depleting all three dioxygenases(Tet1-3),we found that Tet dioxygenases slightly inhibited both early and late apoptosis induced by TCBQ at a low concentration(30 μmol/L).Meanwhile,treated by TCBQ at higher concentrations(40and 50 μmol/L),the total percentage of apoptotic cells was not affected by Tet dioxygenases.However,Tet dioxygenases tended to arrest mouse ES cells to be at early apoptotic stage and to reduce the cells to enter later apoptotic stage.These results indicate that Tet dioxygenases play a role in shaping TCBQ-induced apoptosis in mouse embryonic stem cells.Our study provides new insights into the toxicology of PCP and its reactive metabolite TCBQ. 相似文献
40.
通过区内(竹蜓)类化石资料的整理研究,在黄龙组建(?)带三带五亚带,船山组两个带,并简述其分布规律及与国内外相应地层(?)带的对比。 相似文献