陡山沱组盖帽碳酸盐岩C同位素特征及形成环境——以扬子北缘神农架地区为例
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本文为国家重点研发计划深地资源勘查开采专项(编号2016YFC0601001)、国家自然科学基金项目(编号41472082)、中国地质调查局项目(编号DD20160120- 01)、神农架世界地质公园项目共同资助成果。


Carbon isotopic characteristics and sedimentology of Ediacaran cap carbonates:a case study from the Shennongjia area, northern Yangtze craton
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    摘要:

    神农架地区位于华南扬子克拉通北缘,发育完整的成冰系- 埃迪卡拉系地层层序。本研究基于新近发现的6个埃迪卡拉系盖帽碳酸盐岩剖面,系统研究了其地层学、沉积学和C同位素地球化学特征,并依据盖帽碳酸盐岩发育的一系列沉积指相标志,讨论了盖帽碳酸盐岩形成的沉积环境。神农架盖帽碳酸盐岩由细粉晶白云岩组成,盖帽白云岩与下伏冰碛岩接触关系多较截然,部分为渐变过渡关系,沉积构造单调,以水平层理或块状层理为主,少见其他特殊沉积构造或岩石、矿物组分,偶见团粒、叶枝状等藻类生物,盖帽白云岩和上覆岩系构成快速海侵退积的沉积层序。盖帽白云岩δ13C剖面显示,由下向上从极低(-6‰~-9‰)到中低(-4‰~-5‰)负漂移,或从中下部中低幅负偏逐渐向上更负偏(-4‰~-5‰间)或在中低负值附近高频振荡,但上覆沉积物的δ13C剖面保持持续中低负偏。研究表明,沉积指相标志及C同位素共同指示盖帽碳酸盐岩与冰后期海平面快速上升同步,这6个盖帽白云岩剖面 主要发育于神农架中西部浅水陆架潮坪区域。这些盖帽白云岩剖面的δ13C值基本类同于国内外埃迪卡拉盖帽白云岩δ13C剖面的变化规律,具有广泛的全球变化和对比意义。同时,神农架的这几个盖帽白云岩剖面δ13C值有其独特性,该特征是对冰后初期浅水碳酸盐岩沉积作用平衡全球海平面快速上升的响应。进一步研究发现,埃迪卡拉系初期盖帽碳酸盐岩沉积于扬子克拉通广泛的浅水陆架沉积环境,并非发育于从深水盆地—斜坡—陆架的各个沉积相区。

    Abstract:

    An integrated Cryogenian- Ediacaran sequence developed well in the Shennongjia area, northern margin of the Yangtze Craton, South China. Based on six Ediacaran sections bearing cap carbonates discovered recently in this area and a series of the sedimentary facies, this paper discussed the sedimentary environment of cap carbonates through systematically analyzing the stratigraphy, sedimentology and C- O isotope geochemistry. Cap carbonates in the western Shennongjia were composed of fine powder crystal dolomites have sharply contacts with the underlying tillites (and partly gradually transition), and have monotonous sedimentary structures which are mainly horizontal beddings or block stratifications. There are few other special sedimentary structures or lithological and mineral components, occasionally some cumular spharolite and leaf branchlike algae. The cap dolomites and overlying strata formed the rapid transgression sequence. The δ13 C values of the cap dolomites show a negative drift from extremely low (-6‰~-9‰) to medium low (-4‰~-5‰) in an ascending order, and a change from medium or low negative drift to much negative value, or a change around mediumlow negative values with high frequency oscillation, but δ13 C value of the overlying sediments remained medium- low negative. Sedimentary facies indicator and carbon isotopes study show that the cap carbonate rocks deposited in a shallow water shelf intertidal- supratidal flat, synchronously and diachronically with sea level rapidly rising. The 13 C value of the cap dolomite section at Shennongjia is basically similar to the change rule of the Ediacaran cap dolomite section in the world, with a wide range of global changes and correlation significance. Meanwhile, the 13 C value of the cap dolostone profile at Shennongjia is unique, which should be response to balancing the rapid rise of global sea level for the initial post- ice shallow water carbonate sedimentation. Further study found that the cap carbonates mainly developed in the shallow water shelf tidal in the central- west part of the Shennongjia area, but not in the deep- water basin, slope break and shelf.

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旷红伟,柳永清,彭楠,朱志才,王玉冲,刘海,宋换新,唐永,宋昌贵,范正秀,夏晓旭,陈骁帅.2019.陡山沱组盖帽碳酸盐岩C同位素特征及形成环境——以扬子北缘神农架地区为例[J].地质学报,93(9):2139-2157.
KUANG Hongwei, LIU Yongqing, PENG Nan, ZHU Zhicai, WANG Yuchong, LIU Hai, SONG Huanxin, TANG Yong, SONG Changgui, FAN Zhengxiu, XIA Xiaoxu, CHEN Xiaoshuai.2019. Carbon isotopic characteristics and sedimentology of Ediacaran cap carbonates:a case study from the Shennongjia area, northern Yangtze craton[J]. Acta Geologica Sinica,93(9):2139-2157.

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  • 收稿日期:2019-03-29
  • 最后修改日期:2019-05-05
  • 录用日期:2019-05-11
  • 在线发布日期: 2019-05-24
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