五台山古元古代巨型叠层石的结构特征及成因意义

山西省五台山地区的古元古代滹沱群地层中发育大量各种形态和大小的叠层石,最近在东冶亚群地层中发现体量巨大的叠层石。本文在对其进行形态学分析、显微结构分析、地质剖面实测以及生长环境特征分析研究后认为,这一宏观上的穹窿形叠层石是由柱状叠层石组成的生物岩礁,柱体在底质基础上放射状生长,其表面圆形、长条形的凸起为叠层石柱体顶部横断面及斜切面形态。通过标本切片,镜下观察到组成柱体并充填柱间的均为泥晶方解石,并发现纤细的丝状微生物遗迹,这些丝状体相互交织构成暗层的重要组分。叠层石体量巨大,需要较长时间内相对稳定的深水环境;泥晶方解石结晶较好,指示水动力条件相对较弱、沉积速率较快的温暖浅海环境,可能形成于潮下带。

Structural characterister of a huge Paleoproterozoic stromatolite in Mt. Wutai, and its genetic implication

The Paleoproterozoic Hutuo Group in Mt. Wutai of Shanxi Province yields various types of stromatolite with different size and morphology. Recently a huge stromatolite was discovered in the stratas of Dongye Subgroup there. After morphologic and ultra-structural morphologic characteristic analysis, geological profile measured and relative growing environment analysis, the "domal" stromatolite in macroscopic view is actually a bioherm composed of large amounts of columnar stromatolites which radially grew on the surface of an initial sediment. The round salients and long-strip-shaped ridges on surface are cross and inclined sections of the stromatolite columns. Microcrystalline calcites composing the columns as well as filling space among columnsand are observed in sections under polarizing microscope, so are the remains of tenuous filamentous microorganisms which interweave together to form up the dark layers. The huge architectural mass requires basically a long-period stable environment with deep water. The well-crystallized microcrystalline calcites indicate that the growing environment was warm shallow sea with weak hydrodynamic condition and high deposition rate, perhaps the subtidal zone.