西藏南部晚白垩世厚壳蛤的锶同位素年龄标定  

Strontium Isotope Age Calibration of Rudist Bivalves from Late Cretaceous Section in Southern Tibet

作　　者：黄思静[1] 石和[1] 张萌[1] 武文慧[1] 沈立成[1] 黄成刚[1] 

机构地区：[1]成都理工大学油气藏地质及开发工程国家重点实验室,四川成都610059

出　　处：《地球科学（中国地质大学学报）》2005年第4期437-442,共6页Earth Science-Journal of China University of Geosciences

基　　金：国家自然科学基金项目(No.40272059);国家重点基础研究发展规划项目前期研究专项(No.2001CCA01800).

摘　　要：沉积岩样品年龄的直接标定是沉积学与地层学研究的难点之一.由于锶在海水中的残留时间(≈106a)大大长于海水的混合时间(≈103a),因而同一时间全球海水的锶元素在同位素组成上是均一的,并造成地质历史中海水的锶同位素组成是时间的函数,这是锶同位素地层学(SIS)的基本原理和利用锶同位素地层学进行海相地层定年的理论基础.本文根据锶同位素地层学的基本原理,测试了西藏南部岗巴剖面上白垩统宗山组上段地层中厚壳蛤化石的锶同位素组成,尝试对这些化石进行了年龄标定,4个样品分别位于剖面累计厚度381,362,358和296m处,其87Sr/86Sr比值分别为0.707832,0.707769,0.707768和0.707695,年龄的标定结果分别是65.68,69.34,69.39和72.32Ma,定年的平均误差为±1Ma左右.研究结果表明,锶同位素地层学在海相地层定年方面具有潜在价值.The direct numerical age calibration for sedimentary rocks is more difficult in sedimentology and stratigraphy. The long oceanic residence time of Sr (106 a) and the rapid mixing rate of the oceans (103 a) have caused the strontium isotope ratio of seawater to be globally homogeneous at any given time, as documented by identical 87Sr/86Sr ratios for coeval marine carbonates, and therefore, the 87Sr/86Sr ratios are the function of geological time which is the fundamental principle of strontium isotope stratigraphy (SIS) and the theoretical basis of dating marine sediments using SIS. In this paper, 87Sr/86Sr ratios of 4 rudist bivalves collected from a sedimentary section of the Late Cretaceous in the southern Tibet were measured. Based on the very low Mn/Sr ratio (average 0.01) of the samples, it is thought that they contain information on the original seawater strontium isotope composition. The ages of the fossils were calibrated according to the principle of strontium isotope stratigraphy. The 4 samples are located at 381, 362, 358 and 296 m, respectively, with the accumulation thickness in the section. Corresponding 87Sr/86Sr ratios are 0.707832, 0.707769, 0.707768 and 0.707695, respectively, and the ages calibrated are 65.68, 69.34, 69.39 and 72.32 Ma, respectively. The average error for dating by strontium isotope stratigraphy is approximately ±1 Ma. The research shows a potential value of SIS in dating marine rocks.

关 键 词：西藏南部 晚白垩世 厚壳蛤 锶同位素地层学 海相地层定年 

分 类 号：P53[天文地球—古生物学与地层学]