前寒武纪沉积碎屑岩中有机质壁微体化石的分析处理及观察方法

ANALYSIS AND OBSERVATION OF ORGANIC-WALLED MICROFOSSILS IN THE PRECAMBRIAN SEDIMENTARY CLASTIC ROCKS

前寒武纪是地球演化历史上的重要时期,随着早期生命起源、构造演化、油气勘探等研究的不断深入,前寒武纪越来越受到关注。微体化石是研究前寒武纪生命演化和地层对比的重要窗口,尤其是在新元古代大冰期之前的地层中,主要保存的是体型较小、类型多样的微体化石,而宏体化石则凤毛麟角,仅有为数不多的类型。在许多前寒武纪碎屑岩地层中,以布尔吉斯页岩型方式保存的有机质壁微体化石,是其中保存的唯一的化石类型。但因这些有机质壁微体化石在围岩中遭受了长时间地成岩、变质、风化和剥蚀等作用,在化石处理过程中非常容易破碎,导致获取保存完整的微体化石较为困难,给属种鉴定、生物多样性评估和生物地层对比等研究带来诸多不便。本文主要介绍一种从粉砂岩-泥岩中获取有机质壁微体化石的处理方法,包括样品的碎样、酸处理、富集、挑选、制片和拍照等各流程的详细步骤,以及在分析处理中存在的问题和注意事项。

Precambrian is an important period in the Earth history.With the development study of the early life origin,continental structural evolution,hydrocarbon exploration and so on,more and more attentions have been paid on the Precambrian.Microfossils are one of the important windows to understand the life evolution and stratigraphic comparison in the Precambrian strata.Particularly,the diverse and abundant microfossils are the major fossil types in most pre-Cryogenian successions,while macrofossils are scarce with only a few taxa.In many Precambrian siliciclastic strata,Burgess Shale-type preserved organic-walled microfossils are the only fossil type that can be found.However,organic-walled microfossils are fragile during lab procedure,because they have suffered diagenesis,metamorphism,weathering,and erosion for a very long time.It is difficult to obtain intact specimens of organic-walled microfossils,which hampers our ability in taxonomic classification,biodiversity assessment and biostratigraphy subdivision.This paper mainly introduces the treatment and analysis method of organic-walled microfossils in siltstones and mudstones,discussing various problems and precautions on methods and techniques,especially on the crushing,acid maceration,concentrating,choosing,making slides and photographing.