SEISMOLOGY AND EGOLOGY ›› 1996, Vol. ›› Issue (4): 329-338.

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ISOTOPE STUDIES OF SHIHUA CAVE, BEIJING (Ⅱ):RADIOCARBON DATING AND AGE CORRECTION OF STALAGMITE

Li Hongchun1, Teh-Lung Ku1, Chen Wenji2, Jiao Wenqiang2, Zhao Shusheng3   

  1. 1. Department of Earth Sciences, University of Southern Californica, Los Angeles, CA 90089;
    2. Institute of Geology, SSB, Beijing 100029;
    3. Institute of Geology, Academia Sinica, Beijing 100029;
    4. Department of Archaeology, Peking Uniuersity, Beijing 100871;
    5. Institute of Beijing Geological, survey, Beijing 102206
  • Received:1996-06-30 Online:1996-12-04 Published:2009-11-25

洞穴石笋的14C年代学研究──石花洞研究系列之二

李红春1, 顾德隆1, 陈文寄2, 焦文强2, 赵树森3, 陈铁梅4, 李铁英5   

  1. 1. 美国南加州大学地球科学系;
    2. 国家地震局地质研究所;
    2. 中国科学院地质研究所;
    2. 北京大学考古系;
    2. 北京地质调查所

Abstract: The application of radiocarbon dating of speleothems is often limited by "dead carbon" contamination.In this paper we have established a new model to correct contamination of "dead carbon" and determine growth rate of a stalagmite which was collected from Shihua cave, Beijing.Based on the measurements of 14C activity on 11 samples from the stalagmite, we have found that 5 of the samples have little "dead carbon" contamination and four of the samples contain relatively constant contamination of "dead carbon".The two groups of the samples gives us two linear relationships between natural log of 14C activity and depth with the same slopes but different intercepts.These data results illustrate that the stalagmite has a relatively constant growth rate and no growth hiatus which are the assumptions of the model.Using the model we have reconstructed the chronology Of the stalagmite and obtained a mean growth rate of 0.042 mm/a.The results are in good agreement with the mean growth rate determined by the annual growth banding and the youngest age measured by 210Pb method.

Key words: Carbon-14 dating, Lsotopic age dating, Limestone, Stalagmite growth rate

摘要: 由于受“死碳”的影响,年轻洞穴碳酸盐的14C测年始终受到限制,为此,建立了14C法测定石笋生长速率及校正“死碳”影响的理论模式,从而将石笋的测年时限和精度大大提高。这一理论成功地运用于北京石花洞年轻石笋的定年。利用14法与石笋生长光性年际纹层推算的平均生长速率十分吻合,表明石笋S312的生长速率为0.042mm/a.210Pb法测定石笋顶部的年龄小于100a,与14结果的外推年龄基本相同。这一研究结果为下一步解释稳定同位素的古气候意义奠定了年代学基础。运用14C法测定石笋生长速率要求有足够的数据点进行线性拟合。在线性范围内,要求满足石笋生长速率均匀,生长连续,“死碳”影响程度一致的假设条件。从δ13C和14C强度的对比分析,判断“死碳”的影响可能与气候变化有关。初步认为,湿冷气候条件下有利于石灰岩的溶解,造成“死碳”的影响增加。

关键词: 碳-14年龄测定, 同位素年龄测定, 石灰岩, 石笋生长速率