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Timing of the Nihewan formation and faunas 总被引:2,自引:0,他引:2
Magnetostratigraphic dating of the fluvio-lacustrine sequence in the Nihewan Basin, North China, has permitted the precise timing of the basin infilling and associated Nihewan mammalian faunas. The combined evidence of new paleomagnetic findings from the Hongya and Huabaogou sections of the eastern Nihewan Basin and previously published magnetochronological data suggests that the Nihewan Formation records the tectono-sedimentary processes of the Plio-Pleistocene Nihewan Basin and that the Nihewan faunas can be placed between the Matuyama-Brunhes geomagnetic reversal and the onset of the Olduvai subchron (0.78-1.95 Ma). The onset and termination of the basin deposition occurred just prior to the Gauss-Matuyama geomagnetic reversal and during the period from the last interglaciation to the late last glaciation, respectively, suggesting that the Nihewan Formation is of Late Pliocene to late Pleistocene age. The Nihewan faunas, comprising a series of mammalian faunas (such as Maliang, Donggutuo, Xiaochangliang, Banshan, Majuangou, Huabaogou, Xiashagou, Danangou and Dongyaozitou), are suggested to span a time range of about 0.8-2.0 Ma. The combination of our new and previously published magnetostratigraphy has significantly refined the chronology of the terrestrial Nihewan Formation and faunas. 相似文献
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40Ar/39Ar method is a high precision dating means, of which the age is obtained by contrasting the un- known sample with those of standards. Usually the age of standard is determined by K-Ar method in which the 38Ar spike should be added for measurement. However, the absolute concentration of 38Ar spike is measured through the calibrated standards in turn, al- though occasionally the concentration of 38Ar spike is determined by other dating methods, such as Rb-Sr, U-Pb methods, which is kn… 相似文献
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Wang Fei He Huaiyu Zhu Rixiang Sang Haiqing Wang Yinglan Yang Liekun 《中国科学D辑(英文版)》2006,49(5):461-470
Four international standards, Ga1550, MMhb-1, Lp-6, Bem 4M, and one domestic standard BT-1 have been intercalibrated. The
repeated measurements on MMhb-1 with different mass demonstrate that MMhb-1 is inhomogeneous in age and its average age is
519.8 Ma. The results of Bern 4M and Lp-6 reflect that they have an invariable value of 40Ar*/39Ark (F) and the ages we obtained are consensus with their K-Ar age: Lp-6=127.7Ma; Bern 4M=18.2 Ma. Analyses of BT-1 age spectra,
Ca/K and Cl/K spectra as well as inverse isochrons indicate that the sample is homogeneous and invariable and keeps close
chemically, with its trapped argon isotope composition close to the atmosphere. The dating results show that age values are
reproducible and steady, total fusion age, step-heating age, plateau age and isochron age are in accord with each other within
the error range (2σ). Therefore, we recommend 28.7 Ma as the calibrated age of BT-1.
We also discuss the variation in neutron flux gradients of Beijing 49-2 reactor. It was found that the neutron flux gradient
varies considerably, and more monitors (standard samples) are needed to fix the trend of variation. The coefficient of the
49-2 reactor that transfers the ratio of production rate of 37ArCa/39ArK into Ca/K ratio is 1.78. This is different from that reported earlier, 2.0, which may be caused by the reconstruction of
the reactor. 相似文献
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No apparent lock-in depth of the Laschamp geomagnetic excursion: Evidence from the Malan loess 总被引:2,自引:1,他引:2
ZHU Rixiang LIU Qingsong PAN Yongxin DENG Chenglong ZHANG Rui & WANG Xianfeng . Paleomagnetism Geochronology Laboratory 《中国科学D辑(英文版)》2006,49(9):960-967
Developing an accurate chronological framework is always a key issue in paleoclimatic studies. Magneto- stratigraphy has been a routine tool for such purposes. However, complexities arise for inter-profile correla- tions of magnetostratigraphy due to effects of the lock-in process. One good example is the “mystery” of the mismatching of stratigraphic locations of the Matuyama/Brunhes boundary (MBB) (occurred at ~780 ka) recorded in Chinese loess and marine sedi- ments. Tauxe et al.[1] con… 相似文献
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主要评述了近年来泥河湾盆地磁性地层学的研究进展,包括建立泥河湾组的磁性地层年代格架、厘定泥河湾动物群的时代和确定华北地区早期人类活动年代序列.研究表明:第一,泥河湾组河湖相沉积序列记录了高斯正极性时末期以来的地磁极性特征(松山和布容极性时),即沉积时代始于约2.6Ma.早期人类至少在1.66~0.78Ma期间的大约90万年的时间内长期持续地占据高纬度的泥河湾盆地.泥河湾动物群(包括广义和狭义)的时代为2.0~0.8 Ma.第二,华北地区早期人类已经能够适应东亚高纬度地区冬季风增强、夏季风减弱和干旱化趋势增强的复杂环境变化,尤其能适应中更新世气候转型前后中国北方多变而且不稳定气候条件和生态环境.因此,气候和生态环境的多变性与不稳定性是促进人类进化的重要因素.第三,早期人类走出非洲以后,可能沿不同的路径并以较快的速度扩散到东亚地区.向南越过印度尼西亚的赤道地区,向北至少扩散到40°N的泥河湾盆地. 相似文献
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