西藏岗巴晚白垩世锶同位素曲线的地层学意义及问题讨论

地质历史时期古海洋中的锶同位素组成具有全球基本一致的演化规律 ,并主要受全球性海平面变化影响。根据从西藏岗巴宗山上白垩统剖面中 6 3个海相碳酸盐样品获得的锶同位素测试数据建立了锶同位素演化曲线 ,与北美同时代锶同位素曲线进行了对比 ,证明晚白垩世有一次全球性海平面升降事件 ,在宗山剖面宗山组近底部的年龄值为 89.4 Ma,并讨论了西藏岗巴宗山地区晚白垩世地层划分对比中的一些问题。

STRATIGRAPHICAL SIGNIFICANCE OF THE Sr ISOTOPIC EVOLUTIONAL CURVE OF THE LATE CRETACEOUS OF GANGBA, TIBET WITH DISCUSSIONS ON SOME PROBLEMS

The evolution of strontium isotopic composition in ancient seawater during the geologic history is of a global consistent law and mainly controlled by the global sea-level changes. The fundamental principle of the Sr-isotopic stratigraphy is introduced briefly in this paper. An evolutionary curve of the Sr-isotope composition of the Late Cretaceous was set up based on 63 marine carbonate samples from Zongshan section in Gangba, Tibet. It was correlated with a coeval curve set up by J.M.McArthur et al. in North America. According to the correlation, a global eustatic event during the Late Cretaceous was proved, the age of the base of the Zongshan Formation is about 89.4 Ma in this section. Some problems about the stratigraphical division and correlation were discussed.