重庆城口地区早前寒武系黑色岩系研究:(2)早寒武世硅质岩的沉积环境研究

PRE-EARLY CAMBRIAN BLACK ROCK SERIES IN CHENGKOU DISTRICT,CHONGQING:(2) SEDIMENTARY ENVIRONMENT STUDY OF CHERT IN LOWER CAMBRIAN BASHAN FORMATION

和平、羊儿坝和猪草河剖面是南秦岭槽区巴山组的三个典型剖面,从南向北,这三个剖面的硅质岩厚度逐渐增大。通过对三个剖面硅质岩各种地球化学特征参数的研究分析,结果表明:猪草河剖面最接近火山弧带,为与大陆火山岛弧相邻的弧后盆地,受火山活动的控制很强烈,热水沉积的控制占主要地位;相应的硅质岩和碳酸盐岩都具有强烈的Eu正异常,其中具有高正Eu异常的碳酸盐岩在华南下寒武统尚属首次发现。羊儿坝剖面相当于大陆边缘的深水盆地,热水与海水处于相对平衡的状态。和平剖面最接近大陆边缘,热水的影响很弱,以海水的正常沉积为主,陆源碎屑物质增多。三个剖面沉积相从早到晚的变化体现了南秦岭断陷海槽从拉张到闭合的过程。

In the Bashan Formationin the geosynclinal area, the Zhucaohe, Yang＇ erba and Heping sections represent three typical chert sedimentary facieses. Analysis of various geochemical parameters for the three sections indicates that the Zhucaohe section which is a back-arc basin is closest to the volcanic island arc along the continental margin, affected intensely by volcanism and controlled mainly by hydrothermal sedimentation; the Yang＇ erba section is a deep basin on the continental margin, and the effect of hydrothermal water and seawater is relatively counterbalanced in the sedimentary facies; the Heping section, where the effect of volcanism and hydrothermal sedimentation is relatively weak, is closest to the continental margin. The diversification of chert sedimentary facies in the three sections represents the transformational process of the fault trough of southern Qinling Mountains from pull-apart to sealed state.