安徽巢湖二叠系-三叠系界线微生物岩研究

摘要

Mineralogical and geochemical properties of microbialites collected from the Permian-Triassic boundary in Chaohu, Anhui Province were studied.Besides, experiments on the dissolution of microbialites by HCl were carried out for probing the separation condition between calcite and ankerite.The results show that the samples are homogeneous in composition, with high Si, Al and Mn contents.Calcite, quartz, clay minerals and ankerite are the main phases.Most of the ankerite particles are euhedral, showing either triangle or diamond forms on cross section, and their sizes are roughly equal(~10 μm).Under the conditions that HCl concentration was 0.3% and solid-to-liquid ratio was 1∶50, calcite in microbialites was dissolved totally, while leaving ankerite undissolved.It is suggested that microbialites in the Permian-Triassic boundary was formed under anoxic condition;microorganisms promoted the formation of clay minerals, while had no effect on the formation of carbonates;ankerite was formed through three stages: Fe-carbonate was formed during sedimentation, Fe and Mg was released during diagenesis, Fe and Mg entered into calcite, leading to local dolomitization.%文章对安徽巢湖地区二叠系-三叠系界线微生物岩进行了化学成分和矿物组合分析,同时探索了盐酸溶解法分离样品中不同种类碳酸盐矿物的方法.结果表明,界线微生物岩成分均一,具有较高的Si、Al和Mn含量,主要由方解石、石英、黏土矿物和铁白云石组成,岩性上为泥质、白云质灰岩;岩石中的铁白云石自形程度较高,截面呈正三角形或菱形,晶粒大小在10 μm左右;采用0.3%HCl(固液质量比1∶50)可以有效区分微生物岩中的方解石和铁白云石(前者溶解,后者不溶).研究认为:二叠系-三叠系界线层微生物岩形成于缺氧条件下;微生物促进了黏土矿物的生成,对碳酸盐矿物的生成无影响;铁白云石的生成经历了含铁碳酸盐沉积-碳酸盐去Mg、Fe作用-铁白云石化过程.