陕西镇安西口晚二叠世生物礁剖面新观察

NEW INVESTIGATION OF PERMIAN REEF SECTION IN XIKOU, ZHENAN COUNTY, SHANXI PROVINCE

笔者在观察陕西镇安西口晚二叠世生物礁剖面时,得到与前人研究成果不同的认识,这一地区并未形成生物礁。本文从生物地层学、古生态学、沉积岩石学等几个方面阐述生物滩的存在与发展过程,并提出三种主要碳酸盐岩隆(礁、丘、滩)的区分原则。晚二叠世中国南方普遍发育礁、丘、滩。在广泛研究的同时,也应不断加强三种主要碳酸盐岩隆的对比研究。生物滩研究是碳酸盐岩隆研究的组成部分,正确解释礁、丘、滩的不同成因及其结构特征,对岩相古地理的恢复具有重要意义。

The Xikou section with some calcisponges, bryozoans, colonial corals, brachiopods and echinoderms was described as Upper Permian reef by former researchers in 1987. This paper concluded that this section is that of an organic bank rather than a reef. The evidence is as follows:1. There are well developed thin to thick-bedded, intraclastic-bioclastic limestone rather than massive nonbedded framestone in the Xikou area. Geomorphic convex is not quite clear.2. Original porosity and remaining cavities, which represent the features of reef limestone, are rare within the Xikou section and karst topography are also uncommon.3. Absence of structures of typical reef limestone, such as different generation cemnet of fibrous calcite filled between frame-building organisms, are proved by observation of thin sections in laboratory and re-examination in field.4. Bioclastic limestone and grainstone show a colour of gray brown or brown red, which is different from those light grey reef limestone in South China.5. Quantity of frame-building organisms is not enough, and binding organisms are rare on the whole. There are an abundance of conodonts and foraminifers to be found.6. Calcisponges, bryozoans and colonial corals are generally lay down and many other organisms occurred as skeletal debris or fragments.