| 哥德堡事件在湖泊沉积物中的记录 |
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| 引用本文： | 马醒华,孙知明,胡守云.哥德堡事件在湖泊沉积物中的记录[J].第四纪研究,1994,14(2):162-174. |
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| 作者姓名： | 马醒华 孙知明 胡守云 |
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| 作者单位： | 中国科学院地质研究所，中国科学院西安分院黄土与第四纪地质研究室 |
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| 摘 要： | 本文报道了作者１９９１─１９９２年在江苏省高淳县固城湖沉积物岩芯中所取得的高分辨率磁性地层学研究结果。结果揭示出两个反极性事件，其中位于１２．５ｍ左右深度、年龄为１０３０７—９７２７ａＢ．Ｐ．的一次反极性事件，可能是哥德堡事件(１２０００ａＢ．Ｐ．前后)在该沉积物中的记录，其年龄上的差异可能是因测年误差所致；另一位于５．５ｍ左右深度、年龄为７０８５—７００５ａＢ．Ｐ．的一次反极性事件，在目前国际上已报道的资料中尚无相应年龄的反极性事件可以与之对比，只有朱日祥等在北京房山地区泥炭层中所揭示出的一个年龄为４９８０─４７７０ａＢ．Ｐ．的反极性漂移与之接近，但两者是否为同一事件的反映，甚或该事件本身是否真实存在，目前都还不能肯定，有待今后进一步工作加以证实。
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| 关 键 词： | 湖泊沉积 磁性地层 哥德堡事件 |
THE GOTHENBURG EVENT RECORDED IN LAKESEDIMENTS |
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| Institution: | 1. Insititute of Geomechanics, Ministry of Geology and Mineral Resources;
2. Nanjing Institute of Geography and Liminology, Chinese Academy of Sciences |
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| Abstract: | A result of high resolution magnetostratigraphy obtained from recent sedimentsof Gucheng Lake, Gaochun County, Jiangsu Province, was reported.The total thickness of the sediments is about 18.5m. The lithologic charactersfrom bottom to top are: brownish-yellow, yellowish-grey argillaceous fine sand,fin.e sand, silt and mud with a thickness of about 1.5m; greyish-green, bluish-greyand varicolored silt, argillaceous silt, silty clay of 3m thick; bluish-grey andlight grey sludge, silt and mud interbeds of 3m thick; then a 7m thick section ofgrey sludge with partly sludge and silt thin interbeds; on the top of this section,there is about 4m thick dark grey, black and greyish-brown sludge with occasionallygreyish-brown silt banding. It appears that there is a tendency of varying from coarserto finer from bottom to top.566 samples with a sampling interval of 2-3cm were collected from the drilling core for magnetostratigraphic measurement, in addition, 96 auxiliary sampleswere also collected at some key horizons with different lithologic characters forrock magnetism experimental investigation.First of all, the low frequency (0.46kHz) susceptibility KLF, high frequency(4.6kHz)susceptibility KHF and frequency dependent susceptibility KFD of thesesamples were measured using a Bartington MS2 dual frequency susceptibility meter.The variation of the three kinds of susceptibility with depth and its environmentalimplications will be discussed in another paper later on.Then, to identify the magnetic minerals carrying the remanent magnetizationsof these samples, the Isothermal Remanent Magnetization(IRM) measurements withdifferent heating temperature, the Magnetic Hysteresis Loop measurement and theX-Ray Diffraction analysis were carried out for the auxiliary samples of differentlithologic characters. All of these experimental investigations suggested that thedominant magnetic mineral which carries the remanent magnetization of these samples is Magnetite accompanied with a small amount of Maghemite but also involvedsome Hematite and Goethite as hard components in these samples, and the size ofthese magnetic minerals grains are dominantly of single domain and/or pseudo-singledomain, perhaps some of them are already close to single domain/superparamagneticgrain boundary.The remanent magnetization measurement of these samples were carried out atthe paleomagnetic laboratory of institute of Geophysics, Chinese Academy of Sciences using a 2G755-R superconducting magnetometer. All of the samples were suffered thermal or alternating magnetic field treatment respectively for cleaning the secondary remanent magnetization. Figure 1 shows the results of demagnetizing treatment for some samples, and two antipodal directions of remanent magnetization arerevealed clearly, it means that there really are two polarities present in these samples.Based on the results of remanent magnetization measurement and rock magnetism experimental investigation, a magnetic polarity sequence was established inFigure2, in this sequence, it can be seen clearly that two reversed polarity events(or excursions) are revealed in the lake sediments. The one located at about 12.5mdepth in the core with an age of 10 307-9 727aB.P. is regarded as the record ofGothenburg event (about 12 000aB.P.), the difference in age is thought of beingcaused by the dating uncertainty. The another is located at about 5.5m depth in thiscore, its age was dated as 7 085-7 005aB.P., for which, there is not correlative event or excursion in the results published in the world, only that one revealed byZhu Rixiang from the peat sequence at Fangshan, Beijing, with an age of 4980─4 770aB.P. may be comparable with this, but at the moment , we can not yet makesure whether these two records of polarity reversal correspond to the same polarityevent or excursion, or even that the event or excursion itself really exsist or not,further works will be needed to confirm that. |
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