摘要
三峡地区广泛发育的上震旦统 ,及下伏的南沱组和古城组冰碛层 ,有良好的生物地层控制及全球对比意义。新秭归城附近的雾河剖面 ,自南沱组顶部到水井沱组下部出露有利于化学地层学研究的一系列碳酸盐岩沉积。对这一剖面的碳、氧、锶同位素研究发现 :1)碳、锶和氧同位素在陡山沱组顶部到灯影组底部存在明显异常 ;2 )碳同位素在寒武系 -前寒武系界线附近有负异常 ;3 )碳同位素和锶同位素在剖面上的演化具有全球对比意义 ;4)陡山沱组顶部到灯影组底部的碳、锶同位素异常 ,与可能存在末远古纪的冰期 ,即所谓的“后 Marinoan冰期”有关。
The Late Proterozoic Upper Sinian is well deve loped and widespread in the Three Gorges of the Yangtze River, and is divided into the Duoshantuo and Dengying formations accordingly with good biostratigraphic control and can be correlated world wide. There are two tillite horizons under laying the Upper Sinian, the Nantou Formation above and Gucheng Formation below, and the former is considered corresponding to the Marinoan glacier. A continues carbonate Upper Sinian section is well outcropped at Wuhe near Zigui county, which is suitable for the chemostratigraphic study. The analysis of stable isotopes of C, O, and Sr transecting the Wuhe section reveals significant excursions. 1) Carbon isotope (δ 13 C) dramatically drops from 4‰ to -8‰ (PDB in this paper) near the boundary between the Doushantuo and Dengying formations, and elevates around 4‰ at lower part of Dengying Formation where oxygen isotope (δ 18 O) raises to 0.5‰ from -7‰ at the upper part of the Doushantuo Formation. Strontium isotopic ratio ( 87 Sr/ 86 Sr in this paper) shows a peak as high as 0.7100 across the boundary, which is from 0.7077 in the upper part of the Doushantuo Formation, and 0.7100 in the base and 0.7084 in the lower part of the Dengying Formation. 2) a world wide typical excursions of carbon and strontium isotopes are confirmed across the boundary between Precambrian Cambrian controlled by a complex of small shelly fossils at the top of the section. 3) Abnormal isotopic excursions around the boundary between the Doushantuo and the Dengying formations are the possible evidence of “post Marinoan” ice age.
出处
《微体古生物学报》
CSCD
北大核心
2002年第4期382-388,共7页
Acta Micropalaeontologica Sinica
基金
国家重点研究发展规划项目 ( G2 0 0 0 0 7770 0 )
中科院知识创新方向项目 ( K ZCX2 - 116 )
攀登专项 ( 95-专 - 0 1- 3- 2 )资助
