吉林南部震旦纪万隆组与八道江组之间风化壳的发现

以往地质学家认为吉林省南部震旦纪万隆组与上覆八道江组之间是整合接触。笔者经过野外考察和室内研究 ,认为二者应为风化壳不整合接触关系。化学分析显示 ,风化壳泥岩与下伏母岩白云质灰岩相比化学成分发生巨大变化 ,粘土化矿物元素 (SiO2 Al2 O3 )与CaO和LOI的淋失相反 ,从 13.5 7%增加到 5 5 .6 3% ,具明显的风化成土特征。化学蚀变系数 (CIA)和质量迁移系数分析给出了相同的结果 :CIA值达到了 39.4 3% ,Ca元素的质量迁移系数达到 - 0 .97,几乎全部淋失 ,表明化学风化作用明显。综合研究表明 ,该风化壳处于碳酸盐岩风化成土的第二阶段 ,即母岩中“不溶物”在风化过程中逐步堆积形成残积土的阶段 ,为二级层序界面

The discovery of paleo-weathering crusts between Sinian Wanlong Formation and Badaojiang Formation in southern Jilin Province

Based on field observations and indoor researches, the authors hold that there exists an unconformity between Sinian Wanlong Formation and Badaojiang Formation in southern Jilin, as evidenced by three paleo_weathering crusts discovered there. In the past, however, the contact was believed to be a conformity contact. Chemical analysis shows that there is a remarkable change of chemical components from base rocks to the paleo_weathering crust. Unlike CaO and LOI, the total amount of SiO_2 Al_2O_3 of the weathering crusts has increased from 13.57% to 55.63%, suggesting the existence of an obvious formation process of paleosol. The variation of chemical index of alteration (CIA) and that of moving index of mass from the base rocks to the weathering crust show the same trend. CIA is up to 39.43%, whereas the moving index of mass of Ca is up to -0.97, implying that Ca component has been almost completely depleted. All the above analyses show that these weathering crusts belong to the second paleosol formation stage of carbonate rocks, i.e., they were developed by the accumulation of undissolved materials in base rocks and hence belong to the 2nd_order sequence surface.