摘要
新元古代冰期事件记录了“雪球地球”事件重要的地质信息。塔里木盆地周缘新元古代冰碛岩地层露头发育,是研究新元古代冰期事件的理想基地。由于发育多套新元古代火山岩,盆地东北缘库鲁克塔格地区新元古代冰碛岩地层时代已获得较多年代学数据约束;但盆地周缘其他地区新元古代冰碛岩地层公开报道年代学数据较少,不能准确限定其沉积时代,导致冰期事件对比存在争论。为此,本文选择塔里木盆地研究程度较低的西南缘叶城地区新元古代冰碛岩地层,开展岩石学、同位素年代学、岩石地球化学等研究,明确其冰期沉积特征,约束其沉积时代,开展冰期事件对比,讨论古气候风化条件等。南华系波龙组和雨塘组冰碛岩地层具有较低的化学蚀变指数(CIA),分别代表新元古代2次寒冷的冰川气候记录。冰川沉积及其相邻层位的碎屑锆石U-Pb年代学数据显示,波龙冰期的起始年龄晚于(710±13) Ma,与全球Sturtian冰期对应;雨塘冰期的起始年龄不会早于(656±18) Ma,其结束年龄可被南华系顶界年龄635 Ma或上覆震旦系库尔卡克组碎屑锆石年龄(634±9) Ma限定,与全球Marinoan冰期对应。
The Neoproterozoic glacial events record significant geological information of the Snowball Earth. In the Tarim Basin Neoproterozoic outcrops are well developed along the basin margin, making it an ideal research base for studying Neoproterozoic glaciations. The age of the Neoproterozoic diamictite along the northeastern margin of the basin is constrained from a series of well developed Neoproterozoic volcanic rocks in the Quruqtagh area;however, such constraints are lacking for other basin margin areas due to infrequent reporting of chronology data, which leads to disagreements when comparing glacial events. This project selects the minimally studied Neoproterozoic diamictite along the southwestern margin of the Tarim Basin to perform a multidisciplinary, comprehensive analysis of the mineral’s petrology, isotopic chronology and lithogeochemistry of the deposit so as to determine its glacial deposition characteristics and deposition time as well as to better understand the paleoclimatic weathering conditions. The Nanhua Bolong and Sinian Yutang Formations with low CIA(chemical index of alteration) values represent two distinct episodes of Neoproterozoic glaciations. Detrital zircon U-Pb chronology of the glacial deposits and adjacent beds indicate the starting time of the Bolong glaciation is later than(710±13) Ma and corresponds to the global Sturtian glaciation, and the starting time of the Yutang glaciation is no earlier than(656±18) Ma while its termination time can be constrained by the age of the top boundary of the Nanhuan System(635 Ma) or the detrital zircon U-Pb age of the overlying Sinian System Kulkark Formation(634±9) Ma, which corresponds to the global Marinoan glaciation.
作者
李王鹏
李慧莉
王毅
刘少峰
张仲培
杨伟利
蔡习尧
钱涛
李晓剑
LI Wangpeng;LI Huili;WANG Yi;LIU Shaofeng;ZHANG Zhongpei;YANG Weili;CAI Xiyao;QIAN Tao;LI Xiaojian(Petroleum Exploration and Production Research Institute,SINOPEC,Beijing 100083,China;School of Earth Sciences and Resources,China University of Geosciences(Beijing),Beijing 100083,China;Institute of Geomechanics,Chinese Academy of Geological Sciences,Beijing 100081,China;School of Earth Sciences,East China University of Technology,Nanchang 330013,China)
出处
《地学前缘》
EI
CAS
CSCD
北大核心
2022年第3期356-380,共25页
Earth Science Frontiers
基金
国家自然科学基金项目(41902149,41702238)
中国石化科技部项目(P17046-3)。
