摘要:
本文从三个方面探讨了晚前寒武纪陆表海碳酸盐岩潮坪的清水沉积环境,并归纳出了中元古宙雾迷山组于该环境中的沉积模式:(1)岩石类型,基本上是由沉积白云岩组成,厚达三千余米,伴生有硅岩及微量陆源碎屑;(2)显示了浅水及潮坪沉积环境的叠层石组合及其它各种沉积形相;(3)旋(韵)律性组合,在纵向层序中可以见到多级次套叠的旋(韵)律性沉积,每一部段都寓示着若干赋存于各有既定层位的信息,即它的沉积物、古生物及沉积形相大致上是经常固定的组合。通过上述资料分析,综合归纳出了雾迷山组的陆表海潮坪沉积模式,它是在进积的背景上经历了海侵—海退的演化。
Abstract:
Late-Precambrian sedimentary carbonate rocks are well developed in Jixian County, Tianjin, especially those in the Wumishan Formation. They are about 3000m thick and are dominanted by sedimentary dolostone. In terms of the microscopical features and macroscopical occurrences, the transgressive sediments of the Wumishan Formation can be divided into three sedimentary facies zones. 1. Supratidal zone This is a uppertidal environment in open flat. Sediments are dolarenite and dolrudite which contain terrigenous grains. They are deposited in the environment of low grade momentum of sea water. 2. Intertidal zone The sedimentary area of this zone is from an extension of the supratidal zone flat mentioned above towards the sea. The sediments of this zone are mainly finegrained carbonates which contain silicolites and algites. Overall, this zone belongs to a tidal flat environment which is shelf-beachy facies of epicontinental sea. Sedimentation happens under a rather strong hydrodynamic environment. 3. Subtidal zone It has a sedimentary region of underwater flat being dominanted by relatively open high energy zone and a slope depression of relatively high energy zone on the flat. Overall, this zone belongs to an environment of lower tidal flat of shelf-beachy facies of epicontinental sea. The transgressive sedimentary model of the Wumishan Formation mentioned above can play similar role as Bouma's turbidite sequences in providing g'uidance and prognosis for further researches and offering bases for genetic explanation.
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