雅鲁藏布江南带白垩纪地层划分及特征

Division and characteristics of the Cretaceous formation in southern Yarlung-Zangbo suture zone in Tibet

通过1∶25万区域地质调查,在藏南普兰县拉昂错—萨嘎县旦嘎东雅鲁藏布江结合带南带修康群中发现了大量放射虫化石,通过对该区沉积地层的详细调查,结合放射虫化石对原划修康群进行了充分解体,新厘定出侏罗系至始新统7个组级岩石地层单位,其中白垩系划分为折巴组与桑单林组。折巴组以杂色硅质岩、泥岩和页岩为主,夹砂岩、玄武岩等,与上覆上侏罗统旦嘎组和下伏下白垩统桑单林组呈整合接触关系,含丰富的早白垩世放射虫化石;桑单林组以杂色石英砂岩、砂岩、泥岩、页岩及硅质岩为主,夹玄武岩等,整合于下白垩统折巴组与古近系蹬岗组之间,含丰富的晚白垩世放射虫与有孔虫化石。白垩系折巴组与桑单林组的建立与研究,丰富和完善了中生代特提斯洋盆区(雅鲁藏布江南带地层分区)的岩石地层沉积序列,提高了地层的研究水平,为研究该区沉积古地理环境和大地构造演化提供了新的基础资料。

A large number of Radiolarian fossils were found in the southern Yarlung- Zangbo suture zone of Xiukang Group,Lake Rakshastal- Saga county,eastern Danga region through the 1 ∶ 250 000 regional geological survey. And lithostratigraphic units for seven formation from Jurassic to Eocene are disintegrated through the detailed investigation and the characteristic of Radiolarian fossils. The Cretaceous formations are defined as Zheba Formation and Sangdanlin Formation. The characteristic of Zheba Formation is mainly composed of siliceous rocks,mudstone,shale and basaltic sandstone,and Zheba Formation is a conformity between upper Jurassic Danga Formation and lower Cretaceous Sangdanlin Formation,and it is rich in Radiolarian fossils of lower Cretaceous.The characteristic of Sangdanlin Formation mainly consists of quartz sandstone,sandstone,mudstone,shale and siliceous rocks,intercalated with basalt. Sangdanlin Formation is a conformity between Zheba Formation of Early Cretaceous and Denggang Formation of Paleocene,and it is abundant in radiolarian and foraminifera fossils of Late Cretaceous. The establishment and research about the Zhaba and Sangdanlin Formations of Cretaceous can further enrich the basic information in southern Yarlung- Zangbo suture zone. It also improves our research level and provides new data for the sedimentary palaeogeographic and tectonic study in this area.