苏北燕子埠地区张夏组鲕粒灰岩地球化学特征及成因

Geochemical characteristics and genesis of oolitic limestones of ZhangxiaFormation in Yanzibu area of Northern Jiangsu Province

燕子埠地区大规模出露张夏组厚层状鲕粒灰岩,为苏北地区的古海洋环境研究提供了材料。采用野外观察、镜下鉴定、化学测试等方法,对研究区张夏组下段鲕粒灰岩的岩石学及地球化学特征开展了研究。结果表明:研究区鲕粒灰岩主要由鲕粒和亮晶方解石胶结物组成;微量元素与稀土元素分布特征具有一致性,表明张夏组沉积期海洋环境保持相对稳定;鲕粒灰岩的地球化学特征受陆源物质混染及成岩作用的影响较弱,可用于古环境恢复;综合地球化学和岩石学判别指标,认为研究区张夏组下段鲕粒灰岩形成于炎热干旱、蒸发量大、氧化高能的陆表海边缘沉积环境。以上研究成果可为苏北地区寒武纪古环境恢复提供重要依据。

A wide-range thick-bedded oolitic limestone of Zhangxia Formation is exposed in Yanzibu area,which provides material for the study of paleo-ocean environment in Northern Jiangsu Province.The petrological and geochemical characteristics of oolitic limestone in the Lower Zhangxia Formation were analyzed by field observation,microscopic identification and geochemical test.The results show that the oolitic limestone in the study area is mainly composed of oolitic and bright crystal calcite cements.The distribution characteristics of trace elements and REE are consistent,indicating that the marine environment remained relatively stable during the depositional period of Zhangxia Formation.The geochemical characteristics of oolitic limestone were weakly affected by terrigenous contamination and diagenesis,which can be used for paleoenvironmental restoration.Based on the discriminant indexes of geochemistry and petrology,the authors concluded that oolitic limestone in the Lower Zhangxia Formation in the study area was formed in high-energy epicontinental sedimentary environment,which is hot,dry,evaporative and oxidized,which could provide an important basis for the restoration of Cambrian paleoenvironment in Northern Jiangsu Province.