川东北二叠系-三叠系界线附近微生物岩微观表面特征观察研究

SURFACE MICROSTRUCTURES OF THE MICROBIALITE AROUND PERMO-TRIASSIC BOUNDARY,NE SICHUAN,CHINA

对采自四川通江平溪坝二叠系-三叠系界线(PTB)剖面发育的微生物岩样品,选用2.5%盐酸、10%盐酸、10%氢氧化钠溶液、20%双氧水、10%醋酸以及0.1M乙二胺四乙酸钠(EDTA)进行处理,根据微生物岩表面处理结果的异同,和在扫描电镜(SEM)图像上的表现,确定最适合于微生物岩表面结构观察的化学处理方法是使用2.5%盐酸处理样品表面。用该法处理,并通过SEM观察发现,通常被当作白云岩的PTB微生物岩,实际上只是含有白云岩微晶的泥晶灰岩,微生物岩中含有与硫酸盐还原菌有关的大量的纳米级微球粒与形似草莓状黄铁矿的颗粒。通过实验结果对比分析了不同层位的微生物岩与白云岩的SEM微米级的特征和区别,以及建造微生物岩的微生物群落对其层位上下地层的影响。

A variety of chemical methods were employed to analyze microbialite of the Hongyudong section in Tongjiang,Sichuan Province.2.5%HCl,10%HCl,10%NaOH,20%H2O2,10%HAc and 0.1M EDTA were used to etch the surface of microbialite samples.According to the results of the experiment and SEM,the best chemical condition was selected.Some microbial and metazoan fossils were found on the surface of microbialite after chemical treatment.The differences of surface features between microbialite and general dolomite were compared,and the nano-sized spheroids in microbialite were possibly the traces of sulphate-reducing bacteria activity.A anaerobic environment caused by sulphate-reducing bacteria is suggested as a possible clue to the end-Permian mass extinction.