青海柴达木盆地北缘全吉群内部存在区域性不整合

摘要

Based on field work in this study in combination with previous researches, the authors recognized a regional unconformity within the Quanji Group. This unconformity overlies the Hongzaoshan Formation. It is featured by the iron palaeo-weathering crust, interruption of sedimentation and erosion of the surface over and below the unconformity. There also exist remarkable differ⁃ences of paleontological associations and depositional environment on both sides of the unconformity. The Hongzaoshan Formation beneath the unconformity represents carbonate platform sedimentary facies. The Heitupo, Hongtiegou and Zhoujieshan formations and Xiaogaolu Group overlying the unconformity show the sedimentary environments characterized by transform from glaciofluvial deposit to supralittoral-intertidal zone, suggesting a transgression process after the formation of the unconformity. This unconformity may be related to the extension tectonic activity of the late Neoproterozoic rift setting on the northern margin of the Qaidam Basin. This interpretation indicates that the contact relation between the Hongzaoshan Formation and the Heitupo Formation of the Quanji Group is not a conformable contact as previously believed. This unconformity formed in Cryogenian-Ediacaran period. The differ⁃ences of paleontological associations and depositional environment on both sides of the unconformity may be related to the breakup of Rodinia supercontinent and snowball Earth deglaciation.%通过野外考察和前人资料分析发现，柴达木盆地北缘全吉群红藻山组之上存在一个区域性的不整合，其中发育铁质风化壳、沉积间断、地层的缺失、侵蚀作用特征。不整合面上、下地层存在古生物组合、沉积环境的突变。界面以下为碳酸盐台地沉积，界面之上代表了冰水沉积到海相潮上—潮间带沉积，上覆黑土坡组—红铁沟组—皱节山组，依次沿着不整合面向上超覆，反映了不整合发育之后的又一次海进过程。该不整合界面可能代表了新元古代晚期该地区裂谷盆地的伸展阶段的构造响应。该区域性不整合的发现，改变了以往传统的对全吉群内部整合关系的认识，说明全吉群需要解体。该不整合可能发生于成冰纪—埃迪卡拉纪。该时期的不整合面上、下生物面貌和沉积环境的变化或突变，可能与新元古代晚期罗迪尼亚超大陆的裂解和全球雪球事件相关。