扬子地台寒武系碳酸盐岩的碳同位素组成及地质意义  

Carbon isotope composition of Cambrian carbonate rocks in Yangtze Platform,South China and its geological implications

作　　者：左景勋[1] 彭善池[2] 朱学剑[2] 

机构地区：[1]河南省地质调查院,河南郑州450001 [2]中国科学院南京地质古生物研究所

出　　处：《地球化学》2008年第2期118-128,共11页Geochimica

基　　金：国家自然科学基金(40672023,40332018)

摘　　要：贵州金沙地区寒武系上部娄山关组岩性单一,为蒸发相白云岩,生物化石稀少,沉积时代归属不清。为寻找地层对比与划分的岩石地球化学标志,按5m的样品间距对贵州金沙地区相邻的长岩沟剖面、岩孔剖面寒武系采集了250件碳、氧同位素样品进行测试分析,对其演化趋势进行了研究。结果表明,贵州金沙地区寒武系碳同位素组成演化表现出4次显著负漂移和3次显著的正漂移。负漂移分布于清虚洞组中部(NE-1)、陡坡寺组下部(NE-2)、陡坡寺组与娄山关组的分界处(NE-3)、及娄山关组下部(NE-4),δ13C值分别降低到-2.3‰、-2.6‰、-6.2‰和-4.8‰;正漂移分布于清虚洞组底部(PE-1)、顶部(PE-2)及娄山关组上部(PE-3),δ13C值分别上升到1.3‰、2.1‰和2.6‰。δ13C的演化趋势可与世界各大陆寒武系δ13C演化趋势对比,它将娄山关组下部、中部、上部分别划归全球寒武系第二统上部、第三统及第四统。Loushanguan Formation consists mainly of dolomite in Jinsha area, Guizhou Province, South China. Traditionally it was considered to belong to Upper Cambrian, but because of its containing few fossils, the accurate biostratigraphic correlation with strata in other areas remains unclear. For the purpose of correlation, 250 carbonate rock samples were collected from Changyangou and Yankong sections at intervals of 5 m to analyze carbon and oxygen isotopic compositions. The results show that the evolution curve of carbon isotopic compositions has four negative excursions and three positive excursions in Cambrian. The negative excursions occur in the middle part of Qingxudong Formation （NE-1）, in the lower part of Douposi Formation （NE-2）, and in the lower part of Loushanguan Formation （NE-3 and NE-4） with the minimum δ^13C values of - 2. 3%0, - 2. 6‰, - 6. 2‰ and -4. 8‰, respectively. The positive excursions occur in the basal and uppermost part of Qingxudong Formation （PE-1 and PE-2）, and in the upper part of Loushanguan Formation （PE-3） with the maximum δ^13C values of 1.3‰, 2. 1‰ and 2.6‰, respectively. Carbon isotope excursions tested within Cambrian in Jinsha area, South China correlate well with the excursions which occur in Cambrian System in the world. Therefore, Loushanguan Formation can be subdivided into three parts, with the lower part belonging to the Second Series, the middle part to the Third Series, and the upper part to the Furongian Series within the global Cambrian System.

关 键 词：碳同位素组成 地层对比与划分 寒武系 长岩沟 岩孔剖面 贵州 扬子地台 

分 类 号：P597[天文地球—地球化学]