深水异地鲕粒灰岩的特征及成因探讨——以宁夏中宁地区香山群徐家圈组为例

深水异地鲕粒灰岩可从宏观特征、微观特征、粒度特征及沉积构造等方面进行识别。通过宁夏中宁县狼嘴子地区香山群徐家圈组中部发育的鲕粒灰岩的野外露头剖面和室内薄片观察,对鲕粒灰岩的宏观及微观特征进行了研究。对颗粒粒径的统计和对比分析表明,鲕粒与假鲕、正常鲕与表皮鲕分别来自不同环境,粒度分析结果显示其具有重力流搬运的特征。结合沉积背景认为,此种鲕粒灰岩应为深水异地沉积成因,鲕粒可能来自同时期的鄂尔多斯地块西缘碳酸盐台地,由重力流搬运至深水。

Characteristics and Genesis of Allochthonous Ordovician Limestone: A case for Middle Ordovician Xujiajuan Deepwater Oolitic Limestone in Zhongning Area, Ningxia

Deepwater allogene oolitic limestone can be identified by macroscopic and microscopic features,grain size characteristics and sedimentary structures.Macroscopical and microscopical observation and analysis have done to the outcrop sections and rock thin sections form Middle Ordovician Xujiajuan oolitic limestone in Zhongning Area,Ningxia.The result of statistical analysis and contrast of rock grain sizes has shown that oolites and pseudoolites,normal oolites and epidermis oolites formed in different environments.The granularity is characterized by gravity flow transportation.Combined with the sedimentary background,it is believed that this kind of oolitc limestone is deepwater allogene deposits in origin and the oolites are likely to come from the contemporaneous carbonate platform in the west margin of Ordos Block to this deep water area by gravity flow transportation.