保山地块下二叠统丁家寨组碳同位素特征

Carbon isotope chemostratigraphy of the Lower Permian Dingjiazhai Formation in the Baoshan Block,Yunnan

关键词:  碳同位素  负偏移  碳酸盐岩  冰川作用

Key words:  carbon isotope  negative excursion  carbonate rock  glaciation

摘要:

对保山地块的下二叠统丁家寨组碳酸盐岩、含砾钙质杂砂岩及其上、下层位的碳酸盐岩进行了野外剖面实测、钻孔编录和碳、氧同位素分析测试，发现该地区丁家寨组碳同位素表现出一定的变化规律。丁家寨组之下和之上的碳酸盐岩δ¹³C值偏大（均为正值），而丁家寨组δ¹³C值出现了一至多次负偏移。珊瑚化石和苔藓虫化石分别在铺门前组和丁家寨组中被发现，为其时代的限定提供了新依据。通过与全球其它地区同期碳氧同位素分布的投图对比，发现该时期碳、氧同位素数据因受到冰川的影响而表现出具有较强的线性相关性，这些样品受到了成岩作用的影响。δ¹³C负偏移可能与冰期低水位期沉积和成岩过程中近地表的暴露有关。卧牛寺玄武岩大面积喷发引起的各种效应，包括CO₂含量的升高、全球变暖、风化作用的加强、陆源碎屑输入的增加等多种因素，协同冰川作用共同影响了丁家寨组海洋无机碳同位素的变化。

Abstract:

The present paper deals,on the basis of section measurement and borehole geological records,with the carbon and oxygen isotope study of the carbonate rocks and gravel-bearing calcareous greywacke from the Lower Permian Dingjiazhai Formation in the Baoshan Block,Yunnan. The δ¹³C values of the carbonate rocks both in the overlying and underlying horizons of the Lower Permian Dingjiazhai Formation are positive values while those within the Dingjiazhai Formation display one or several negative excursions. The coral and bryozoan fossils found separately in the Pumenqian and Dingjiazhai Formations have provided the new evidence for the age dating of the Formatioms mentioned above. The correlation between the carbon and oxygen isotope values for the Dingjiazhai Formation and other places in the world suggests a highly linear correlation of the carbon and oxygen isotope data during the Carboniferous-Permian. The negative excursions of δ¹³C values may well be related to the surface exposure during the deposition and diagenesis of the glacial lowstand deposits. Numerous factors such as the increase of CO₂ contents,global warming,strengthening of weathering,and the increase of terrigenous supply caused by the large-scale eruption of the Woniusi basalts as well as the glaciation have exerted the combined effects on the variations in marine inorganic carbon isotope values for the Dingjiazhai Formation.