氢氟酸浸解法研究华南陡山沱组燧石结核中硅化疑源类初探

HYDROFLUORIC ACID MACERATION EXPERIMENT TO EXTRACT SILICIFIED ACRITARCHS FROM THE CHERT NODULES OF THE DOUSHANTUO FORMATION, SOUTH CHINA

华南埃迪卡拉系陡山沱组燧石结核中保存丰富的疑源类化石,对它们的研究一直以岩石切片为手段,这在很大程度上影响到对其三维形态的恢复、系统分类的讨论,以及不同埋藏相下化石组成的对比。本研究尝试用氢氟酸浸解燧石结核来获取立体保存的疑源类标本。本实验使用4%(体积分数)的稀氢氟酸配合20目和400目尼龙筛网,以每2-3小时一次的频率收集酸浸解残余,从来自宜昌地区晓峰河和五指山剖面的陡山沱组二段燧石结核中获得了一些硅质标本,包括立体保存的球状疑源类和疑似化石的片状标本。其中,球状疑源类保存了膜壳塑性变形、膜壳外板片状装饰、内部小球体等结构特征,与从燧石结核岩石薄片中获得的标本和从磷块岩中酸浸解获得的立体磷酸盐化标本完全可以对比;它们的保存状态显示多数标本为疑源类的硅质铸模。本研究表明,作为岩石薄片法的重要补充,氢氟酸浸解法在分离和研究埃迪卡拉系燧石中保存的硅化疑源类上有较大潜力。

In the past,investigations on microfossils preserved in the chert nodules of the Ediacaran Doushantuo Formation in South China have been conducted based on the thin section observation,which makes the three-dimensional morphological reconstruction and systematic discussion of the silicified acritarchs,as well as comparison of fossil composition among different taphonomic facies very difficult.In this study,we carried out hydrofluoric acid maceration experiment to extract acritarch specimens from the chert nodules of the Doushantuo Formation collected from the Xiaofenghe and Wuzhishan sections in the Yichang area.Using diluted HF solution(~4%volume percentage),20 mesh and 400 mesh nylon filter clothes,and with undissolved residuals collected every 2-3 hours,silicified specimens were found within the maceration residuals of the chert nodules,including three-dimensional spheroidal acritarchs and some unidentifiable,plate-like specimens.Vesicle flexibility,plate sculpture of vesicles,and internal bodies which are commonly observed in thin sections and three-dimensional phosphatized specimens,are also present in specimens obtained from this maceration experiment;their surface structure and composition suggest that these specimens are mostly internal or outer molds of the original acritarch vesicle.The present work indicates that in addition to thin section observation,the hydrofluoric acid maceration can be used to study silicified acritarchs from the chert preserved in the Doushantuo Formation.