湘西寒武系鼓山阶底界附近碳同位素组成演化趋势  

Carbon isotope trend around the base of the Drumian Stage in western Hunan,South China

作　　者：左景勋[1] 彭善池[2] 朱学剑[2] 方怀宾[1] 祁玉平[2] 陈泳霖 ZUO Jing-xun;PENG Shan-chi;ZHU Xue-jian;FANG Huai-bin;QI Yu-ping;CHEN Yong-lin(Henan Institute of Geological Survey,Zhengzhou 450001,China;Nanjing Institute of Geology and Palaeontology,Chinese Academy of Sciences,Nanjing 210008,China)

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,江苏南京210008

出　　处：《地球化学》2018年第5期453-462,共10页Geochimica

基　　金：国家自然科学基金(41672028;40672023;41672002)

摘　　要：湘西王村剖面寒武系鼓山阶(Drumian)底界附近碳酸盐岩的δ^(13)C值分布于0.5‰~–3.0‰之间,δ^(18)O值分布于–4.0‰~–12.0‰之间,少数碳酸盐岩样品的δ^(18)O值低于–10.0‰,指示岩石经历成岩期后蚀变作用影响,但δ^(13)C、δ^(18)O之间的非协变关系指示碳同位素组成比较稳定。鼓山阶底界附近δ^(13)C表现为负漂移演化趋势,负漂移幅度为4.0‰,最低值出现在鼓山阶底界之上9 m处,与美国犹他州Drum Mountains剖面鼓山阶负漂移(DICE)出现的位置基本一致,负漂移幅度可与美国内华达州Desert Range剖面、Panaca Hills剖面、犹他州House Range剖面、Drum Mountains剖面对比,表明DICE负漂移具有洲际可对比性,可作为寒武系鼓山阶划分与对比的工具。湘西王村剖面寒武系第二统顶部清虚洞组、第三统底部敖溪组白云岩为海平面下降期形成的进积序列,寒武系第三统花桥组下部黑色泥灰岩、钙质泥岩夹富含黄铁矿结核的硅质条带为深水斜坡相沉积,超覆于白云岩之上。因此,寒武系鼓山阶底部附近的DICE负漂移发生在寒武纪第三世鼓山期海侵时期,与美国Drum Mountains剖面鼓山阶DICE负漂移所处的沉积环境相似。Theδ13C of carbonate samples collected around the base of the Drumian Stage in the Wangcun section,western Hunan,South China,ranged from 0.5‰to–3.0‰,andδ18O values ranged from–4.0‰to–12.0‰.A few carbonate samples hadδ18O values of less than–10.0‰,thereby indicating that the carbonates experienced diagenesis.However,values ofδ13C andδ18O showed no covariance,which implied that the carbon isotopic composition is relatively stable.One negative carbon isotope excursion was detected around the base of the Drumian Stage of the Cambrian.Moreover,the amplitude of this negative excursion was 4.0‰and the minimum value ofδ13C occurred at 9 m above the base of the Drumian Stage,and all these characteristics were similar to the negative DICE(Drumian carbon isotope excursion)tested in the Drum Mountains section in Utah,USA.The range inδ13C varied,and the position where the carbon isotope excursion occurred in the Wangcun section in western Hunan,South China could be compared with that in the Panaca Hills section and the Desert Ridge section in Utah,as well as the House Range section and the Drum Mountains section in Utah,USA,thereby suggesting that the negative DICE can be used as an indicator for correlation between the Drumian Stage in different continents.In addition,dark marl limestone and calcareous mudstone containing tubular pyrite in siliceous ribbons in the lower part of the Huaqiao Formation were deposited on a deep-water ramp during sea-level rise.In contrast,dolomite of the Qingxudong Formation in the upmost part of Series 2 and dolomite of the Aoxi Formation in the basal part of Series 3 were deposited during sea-level fall.Consequently,the negative DICE occurred in a transgressive succession in early Epoch 3 at the Wangcun section in western Hunan,South China,which is similar to that in the Drum Mountains section in Utah,USA.

关 键 词：碳同位素组成 DICE负漂移 鼓山阶 寒武系 湘西王村 

分 类 号：P597[天文地球—地球化学]