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    四川盆地南北缘志留系的锶和碳、氧同位素演化及其地质意义

    Strontium,carbon and oxygen isotopic compositions and their geological significance:the Silurian strata on the northern and southern margins of the Sichuan Basin

      摘要
    • 摘要: 通过对四川盆地北缘广元地区及南缘綦江地区上奥陶统及下志留统地层的87Sr/86Sr、δ13C及δ18O的系统测定,取得了沿地层剖面变化的同位素组成规律。研究结果表明,在盆地南缘87sr/86Sr值高于地质历史中海水的平均值,其原因是本区为受板块内古陆控制的缓坡环境,大量陆源锶的混入增加了87Sr/86Sr的值。87Sr/86Sr值在上奥陶统至下志留统地层交界处、Rhuddanian/Aeronian（鲁丹期/艾隆期）交界处具正峰波动,反映了此时海平面的短时下降。但从Rhuddanian至Telychian（特里奇期）,87Sr/86Sr逐渐降低。从Aeronian至Sheinwoodian（舍因伍德期）早期,盆地南北缘的δ13C值处于逐渐上升的过程之中,而δ18O则相反。同位素的演化特征说明本区当时为海进时期,海平面不断上升,与全球性海平面变化相吻合。由于受区域构造运动的作用,Sheinwoodian之后的全球持续海进对本区无影响。

       

      Abstract: The Sr,C and O isotopic compositions across the stratigraphic section have been ob-tained in the light of the systematic determinations of 87Sr/86Sr,δ13C and δ18O values for the Upper Ordovician-Lower Silurian strata in the Guangyuan region of the northern margin and Qijiang region of the southern margin of the Sichuan Basin.On the basis of the isotopic data in combination with the sedimentary facies and tectonic data and the published infor-mation about the global Silurian regressive-transgressive events,the following conclusions can be drawn.

       

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