华北寒武系芙蓉统底界附近的碳同位素组成演化特征

Carbon Isotope Trend across the Base of Furongian Series of Cambrian,Northern Henan,North China

为了确定我国华北寒武系苗岭统鼓山阶和芙蓉统排碧阶的底界,对豫北沙滩剖面碳酸盐岩碳同位素组成演化趋势进行了研究.结果表明寒武系δ^13C演化表现出3次正漂移和2次负漂移,正漂移分布于张夏组下部、中部和炒米店组上部,δ^13C分别达到最大值2.0‰、1.0‰和3.0‰;负漂移分布于张夏组底部和中下部,δ^13C分别降到最低值-3.4‰和-1.0‰.炒米店组上部的δ^13C正漂移起始于三叶虫Chuangia带底部,相当于美国、澳大利亚、西伯利亚及我国华南地区的芙蓉统排碧阶的SPICE正漂移.张夏组底部的δ^13C负漂移对应于三叶虫Bailiella-Lioparia带,相当于鼓山阶底部的DICE负漂移.这2次δ^13C漂移事件不仅可作为区域地层对比的依据,还可作为我国华北寒武系苗岭统鼓山阶和芙蓉统排碧阶底界确定的标志.寒武纪δ^13C漂移事件与海平面变化、古生态环境演化密切相关,因海侵作用导致的古生态环境扩大及海洋初始生产力的繁盛可能是海相碳酸盐岩δ^13C正漂移演化的主要原因.

In order to define the base of the Drumian Stage and the base of the Paibian Stage of Cambrian in North China,carbon isotope trend is studied on the Shatan section,northern Henan.Data of carbon isotope suggest that three positive excursions and two negative excursions have been examined within the measured stratigraphical interval.Positive carbon isotope excursions occur separately in the lower part and the middle part of the Changhia Formation and in the upper part of the Chaumitien Formation,maximum δ^13C values of these positive excursions reach to 2.0‰,1.0‰and 3.0‰respectively.Negative δ^13C excursions occur in the basal and the lower-middle part of the Changhia Formation with the minimum values of-3.4‰and-1.0‰respectively.Especially,the remarkable positive excursion examined in the upper part of the Chaumitien Formation commences on the base of the trilobite Chuangia zone,which corresponds to the base of the Paibian Stage in South China and is equivalent to the SPICE excursion detected in the Paibian Stage in USA,Australia,and Kazakhstan.The negative excursion examined in the basal part of the Changhia Formation is equivalent to the DICE excursion.Both the two carbon isotope excursions are not only used as tools for the regional stratigraphical classification and correlation,but also used as key indicators in defining the Drumian Stage and the Paibian Stage in North China.In addition,carbon isotope excursions are interpreted to be associated with global scale sea-level fluctuations,paleoecological environmental changes.Seawater transgression together with enlargement of paleoecological environment played an important role in positive carbon isotope excursions during the Late Miaolingian to the Early Furongian.