柴达木盆地东部扎布萨尕秀组的时代归属讨论  

Discussion on the depositional timing of the Zhabusagaxiu formation in the eastern Qaidam Basin,China

作　　者：马立成 江万[1,2,3] 肖宙轩 李宗星[1,2,3] 彭博 胡俊杰 董敏[1,2,3] MA Licheng;JIANG Wan;XIAO Zhouxuan;LI Zongxing;PENG Bo;HU Junjie;DONG Min(Key Laboratory of Paleomagnetism and Paleostructure Reconstruction,Ministry of Natural Resources,Beijing 100081,China;Institute of Geomechanics,Chinese Academy of Geological Sciences,Beijing 100081,China;Key Laboratory of Petroleum Geomechanics,China Geological Survey,Beijing 100081,China;School of Earth Science and Resources,Chang′an University,Xi′an 710054,Shannxi,China)

机构地区：[1]自然资源部古地磁与古构造重建重点实验室,北京100081 [2]中国地质科学院地质力学研究所,北京100081 [3]中国地质调查局油气地质力学重点实验室,北京100081 [4]长安大学地球科学与国土资源学院,陕西西安710054

出　　处：《地质力学学报》2020年第6期961-972,共12页Journal of Geomechanics

基　　金：中国地质调查局地质调查项目(DD20190094)。

摘　　要：柴达木盆地石炭系是中国北方新区新层系油气勘探调查研究的热点,盆地东部地区石炭系出露较全,但多数学者认为柴东地区不存在二叠系。针对扎布萨尕秀组归属于石炭纪还是二叠纪的争议,采集扎布萨尕秀组的砂岩碎屑锆石开展了U-Pb LA-ICP-MS同位素测年,获得40个和谐年龄分布在2488±34 Ma至288±3 Ma之间,最年轻的一组碎屑锆石的加权平均年龄288.0±2.0 Ma(MSWD=0.112,n=21)。这意味着该扎布萨尕秀组中的砂岩沉积于288 Ma之后,晚于国际石炭—二叠纪界限(299 Ma)。依据野外调查和已有研究成果,扎布萨尕秀组中赋存丰富的虫筳科化石,其中膨胀型虫筳属Pseudoschwagerina或Sphaeroschwagerina的出现是进入二叠纪的重要标志。结合碎屑锆石年代学和虫筳属化石特征,扎布萨尕秀组应归属早二叠世,说明柴达木东部地区存在二叠纪沉积记录。该认识为深化柴达木盆地晚古生代—中生代沉积建造和构造演化提供了重要的地层学证据。The Carboniferous hydrocarbon exploration in the Qaidam Basin,Qinghai province in northern China,is the focus in the investigation of newly developed area and new series of strata.The Carboniferous sedimentary strata are fully exposed in the eastern part of the Qaidam Basin,and it has been assumed that there are no sedimentary strata of Permian.Nowadays,it is still controversial whether the Zhabusagaxiu formation belongs to the Carboniferous or Permian.In this paper,detrital zircons from sandstones of the Zhabusagaxiu formation were collected and the zircon U-Pb LA-ICP-MS isotopic dating was carried out.The harmonious ages of zircons were obtained,ranging from 2488±34 Ma to 288±3 Ma.The weighted average age of the youngest group is 288.0±2.0 Ma(MSWD=0.112,n=21).This means that the deposition of sandstones in the Zhabusagaxiu formation happened after 288 Ma,later than the international Carboniferous-Permian boundary(299 Ma).Based on the field investigation and previous research,there are abundant fossil families of Fusulina in the Zhabusagaxiu formation,and especially the appearance of pseudoschwagerina or spyroschwagerina is a crucial sign of entering the Permian.Consequently,combined with the zircon geochronology of classic rocks and typical fossil characteristics in the strata,it is suggested that the Zhabusagaxiu formation should belong to the Early Permian,indicating the existence of Permian stratigraphic deposition in the eastern Qaidam Basin.This recognition provides a geological basis for deepening the sedimentary formation and structural evolution from the late Paleozoic to Mesozoic in the Qaidam Basin.

关 键 词：柴达木盆地 扎布萨尕秀组 碎屑锆石 虫筳属 二叠系 年代学 

分 类 号：P534.[天文地球—古生物学与地层学]