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寒武纪早期是地球海洋环境与生命演化的关键时期,但目前扬子东南缘深水相区的早寒武纪地层尚缺乏系统、精确的地层对比工作。该文选取湖南省怀化地区会同钻孔剖面(深水相区)的留茶坡组硅质岩、小烟溪组黑色页岩为研究对象,进行了高分辨的有机碳同位素(δ~(13)C_(org))地层对比,结果在会同剖面自下而上识别出四个正漂移(P1、P2、P3和P4)与两个负漂移(N1和N2),结合其他剖面的生物化石记录和锆石U-Pb年龄资料,将会同剖面有机碳同位素与湖南其他剖面,以及和云南和三峡等地浅水相区剖面的有机碳、无机碳同位素曲线进行对比,认为扬子东南缘埃迪卡拉系-寒武系界线在湖南深水相区可放置于留茶坡组上部较大的有机碳同位素负漂移(Basal Cambrian Carbon isotope Excursion,BACE)出现的位置,但由于钻孔深度不够,所以该负漂移未在会同剖面获得,而P1、P2和P3分别对应于寒武系的ZHUCE(ZHUjiaqing Carbon isotope Excursion,第二阶)、CARE(Cambrian Arthropod Radiation isotope Excursion,第三阶)和MICE(MIngxinsi Carbon Isotope Excursion,第四阶)正漂移,N1和N2分别对应于寒武系的SHICE(SHIyantou Carbon isotopeExcursion,第二阶)和AECE(Archaeocyathid Extinction Carbon isotope Excursion,第四阶)负漂移,因此会同剖面留茶坡组顶部至小烟溪组底部属于寒武系第二阶,小烟溪组下部属于寒武系第三阶,而小烟溪组中-上部属于寒武系第四阶,而顶部是否达到第四阶顶部尚无法确认。碳同位素的负漂移可能是海侵时期上升流水体将底层富含12C还原水体带至浅水地区所致,并分别与埃迪卡拉动物群、小壳化石动物群和古杯动物的灭绝密切相关;而在生物繁盛时期,海洋初级生产力升高,有机质埋藏增加,导致碳同位素的正漂移。
The early Cambrian period was the key period for the evolution of marine environment and life. However, there is a lack of systematic and accurate stratigraphic correlation in the Early Cambrian strata in the deep-water area of the southeastern margin of Yangtze River. In this paper, we selected the siliceous rocks from the Shibeipo Formation and the Xiao Shanyi Formation black shale in the Huaihua area of Hunan Province as the study objects, and carried out the high resolution organic carbon isotope (δ ~ (13) (Org) stratigraphic correlation, four positive shifts (P1, P2, P3 and P4) and two negative drifts (N1 and N2) are identified from the bottom to the top of the synchronic cross-section, combined with biofuels records from other sections Zircon U-Pb age data will be compared with organic carbon and inorganic carbon isotope curves of other sections of Hunan Province and other regions in Hunan Province and the Three Gorges area. It is concluded that the Eddy- The Cambrian boundary can be placed in the upper part of the Upper Cambrian Carbon isotope Excursion (BACE) in the deep-water-phase region of Hunan, but due to insufficient drilling depth, the negative drift Are obtained in the same section and P1, P2 and P3 correspond to the ZHUCE (second order), Cambrian Arthropod Radiation isotope Excursion (CARE) and MICE (MIngxinsi Carbon Isotope Excursion, Fourth order) are now drifting, N1 and N2 correspond to the negative excursions of SHICE and ICE in the Cambrian, respectively The lower part of Xiaoyanxi Formation belongs to the second order of Cambrian, the lower part of Xiaoyanxi Formation belongs to the third order of Cambrian, while the middle-upper part of Xiaoyanxi Formation belongs to the fourth order of Cambrian, while the top reaches the fourth order Top can not confirm. The negative excursion of carbon isotope may be caused by the updip stream during the transgression period, which is caused by the basal rich 12C reduced water body to the shallow waters, and closely related to the extinction of Edicala fauna, small shell fossil fauna and ancient beagles. In the prosperous period of biology, the primary productivity of the oceans is increased and the burial of organic matter is increased, leading to the positive drift of carbon isotopes.