生物碎屑灰岩的沉积环境和Sr同位素定年:以华北板块北缘二叠纪三面井组为例  

Sedimentary Environment and Sr-isotope Dating of Bioclastic Limestone:A Case Study of Permian Sanmianjing Formation in the Northern Margin of the North China Plate

作　　者：施立志 汪彪 黄静宜[3] 罗立艳 SHI Lizhi;WANG Biao;HUANG Jingyi;LUO Liyan(Chinese Academy of Geological Sciences,Beijing 100037,China;Research Institute of Exploration and Development,PetroChina Xinjiang Oilfield Company,Karamay 834000,Xinjiang,China;Institute of Disaster Prevention,Langfang 065201,Hebei,China)

机构地区：[1]中国地质科学院,北京100037 [2]中国石油新疆油田分公司勘探开发研究院,新疆克拉玛依834000 [3]防灾科技学院,河北廊坊065201

出　　处：《大地构造与成矿学》2023年第6期1430-1441,共12页Geotectonica et Metallogenia

基　　金：地质调查项目“羌塘盆地雀莫错凹陷页岩油气地质调查、羌塘盆地阿木错凹陷油气地质调查(DD20221855)”;国家自然科学基金项目(41572098)联合资助。

摘　　要：为明确广泛出露于华北板块北缘三面井组的地层时代,本文报道了康保县三面井剖面和正镶白旗朝海图剖面三面井组一段下部生物碎屑灰岩发育的古生物特征和差异以及生物碎屑灰岩的Sr同位素组成特征,并运用Sr同位素进行了地层年龄限制。三面井组一段下部生物碎屑灰岩中的生物碎屑丰度较高,保存完好,两个剖面的生物种类存在差异。其中三面井剖面主要是有孔虫([竹蜓]类为主)、腕足类和介形类,形成于滨海高能环境;而朝海图剖面主要是藻类、苔藓类、棘皮类、海绵类、腹足类和腕足类,有孔虫([竹蜓]类为主)相对少见,形成于滨海高能带-浅海低能环境。生物碎屑灰岩的^(87)Sr/^(86)Sr值范围在0.707556~0.708130之间,平均值为0.707748,这与同期全球海水Sr同位素组成相当。与全球海水Sr同位素演化曲线进行标定,结果显示研究区三面井组一段下部的生物碎屑灰岩形成年龄不晚于276.55Ma,结合前人研究,认为其形成时代为早二叠世空谷阶(Kungurian)中期。To determine the stratigraphic age of the Sanmianjing Formation,which is widely exposed in the northern margin of the North China Plate,the paleontological characteristics and differences,as well as the whole rock Sr isotopic compositions of the bioclastic limestones in the lower part of the first member of the Sanmianjing Formation from the Sanmianjing profile in Kangbao County and the Chaohaitu profile in Zhengxiangbaiqi were investigated.The bioclastic abundance of the bioclastic limestones in the lower part of the first member of the Sanmianjing Formation is high and the bioclastic is well preserved,what’s more,there are differences in paleontological species between the two sections.The paleontological species in the Sanmianjing profile are mainly Foraminifers(mainly Fusulinids),Brachiopods and Ostracods,which were formed in the coastal high-energy environment.On the other hand,they are mainly Algae,Bryophyta,Echinodermata,Sponges,Gastropods and Brachiopods,rarely Foraminifers(mainly Fusulinids)in the Chaohaitu profile,which were formed in the coastal high-energy zone to low-energy environment in shallow sea.The 87Sr/86Sr values range from 0.707556 to 0.708130,with an average value of 0.707748,which is the same as the global seawater Sr isotopic composition during the same period.Projection ages of Sr isotopic compositions of the bioclastic limestones from the Sanmianjing Formation are consistent with the global Sr isotopic composition evolution curve.The results demonstrate that formation of the bioclastic limestones in the lower part of the first member of the Sanmianjing Formation in the study area is no later than 276.55 Ma.Combined with previous research results,it is considered that the stratigraphic age of the Sanmianjing Formation is the middle Kungurian of the early Permian.

关 键 词：三面井组 生物碎屑灰岩 SR同位素 沉积环境 地层时代 

分 类 号：P597[天文地球—地球化学]