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    四川盆地晚震旦世古海洋环境恢复及地质意义

    Reconstruction of the late Sinian paleo-ocean environment in Sichuan basin and its geological significance

    • 摘要: 提要:基于四川盆地灯影组3个采样点69组碳氧同位素样品测试分析,在充分论证样品有效性的基础上,对研究区碳氧同位素特征展开分析,进而探讨对应的古海洋环境及地质学意义。四川盆地灯影组白云岩δ13C值分布在-2.85‰~4.44‰,平均值为1.8‰;δ18O值为-9.02‰~-1.90‰,平均值为-5.42‰,碳氧同位素整体变化趋势与中国扬子地台其他区域基本相同。古海洋环境恢复表明,震旦纪灯影期研究区整体处于海相环境;灯影期海水温度主要介于15~30℃之间,属温暖或炎热的亚热带气候;海平面共经历了缓慢海进、低位振荡海退、高位振荡海退、短暂海进、持续海退、振荡海退六个阶段。在海平面升降、气候变化、构造运动以及火山活动等众多因素的影响下,灯影组白云岩δ13C值共出现4次负漂移(N1~N4)和2次正漂移(P1~P2);受古海洋环境的影响,盆地沉积了特征明显的灯二段葡萄状藻云岩、灯三段暗色碎屑岩以及灯四段富藻云岩。

       

      Abstract: Abstract:On the basis of carbon and oxygen isotopic compositions of 69 dolomite samples collected from three sampling points of the Sinian Dengying Formation in Sichuan basin and the effectiveness evaluation of the data, the authors studied the changing characteristics of carbon and oxygen isotopes with the purpose of further reconstructing the corresponding paleo-ocean environment and investigating its geological meaning. The δ13C values of dolomite in Dengying Formation vary from -2.85‰ to 4.44‰ with a mean value of 1.80‰ and the δ13Cvaries vary between -9.02‰ and -1.90‰, -5.42‰ on average. The changing trends of the carbon and oxygen isotopes are similar to those in other strata of the same period in the Yangtze platform. Through the reconstruction of paleo-ocean environment, the authors found that the Sichuan basin of Late Sinian Dengying period was in a marine environment, and the seawater temperatures varied mainly between 15℃ and 30℃, suggesting a warm or hot subtropical climate. The sea level experienced six stages in Dengying period in the study area, i.e., slow transgression, lowstand oscillatory regression, highstand oscillatory regression, transient transgression, sustained regression and oscillatory regression. Under the influence of sea level fluctuation, climate change, tectonic movement and volcanic activity, four negative δ13C anomalies (N1~N4) and two positive δ13C anomalies (P1~P2) occurred in dolomite of Dengying Formation. The basin was filled with easily-recognized grape-sized algal dolomite in Deng2 Member, dark clastic rock in Deng3 Member and algal dolomite in Deng4 Member because of the influence of the paleo-ocean environment.

       

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