西藏仲巴县仁多地区早三叠世牙形石及冈底斯西部早三叠世古地理格局  

The Early Triassic Conodonts in Rendo Area of Zhongba County, Tibet, and Paleogeographic Pattern of the West Gangdise Block in Early Triassic

作　　者：武桂春[1] 纪占胜[2] 孙倩 石秋圆 何继富[3,2] 李浩[2,3] 刘振宇 郭安臣 侯召硕[4] 李东泽[4] WU Gui-chun;JI Zhan-sheng;SUN Qian;SHI Qiu-yuan;HE Ji-fu;LI Hao;LIU Zhen-yu;GUO An-chen;HOU Zhao-shuo;LI Dong-ze(Key Laboratory of Stratigraphy and Paleontology,Ministry of Land and Resources,Institute of Geology,Chinese Academy of Geological Sciences,Beijing 100037;Chinese Academy of Geological Sciences,Beijing 100037;China University of Geosciences(Beijing),Beijing 100083;Geological Survey Institute of Jilin Province,Changchun,Jilin 130102)

机构地区：[1]中国地质科学院地质研究所,国土资源部地层与古生物重点实验室,北京100037 [2]中国地质科学院,北京100037 [3]中国地质大学(北京),北京100083 [4]吉林省地质调查院,吉林长春130102

出　　处：《地球学报》2018年第4期409-418,共10页Acta Geoscientica Sinica

基　　金：国家自然科学基金项目(编号:41472030);科技基础性工作专项(编号:2015FY310100);中国地质调查局基础性公益性矿产地质调查项目(编号:DD20160120-02;DD20160120-04;DD20160126);中国地质科学院基本科研业务费项目(编号:J1607)联合资助~~

摘　　要：随着海相三叠系沉积地层的发现,冈底斯地区三叠纪时期的古地理格局正在经历着从古陆向海洋沉积区的认识上的转变,然而仍然有地质学家认为冈底斯西部南侧存在早三叠世的隆起区,在岩相古地理上表现为隆格尔—工布江达陆相岩浆弧的存在,其主要根据是没有发现三叠系地层。仁多剖面位于该岩浆弧带中部的隆格尔隆起区上,前人认为该区没有下三叠统,然而笔者在以往划分为中二叠统“下拉组”的地层中获得了典型的早三叠世牙形石属Pachycladina的化石,因此确定研究区的下三叠统是存在的,并且在岩性上以白云岩为特征,在区域上可对比到上二叠统至下三叠统的木纠错组的上段。该发现表明仁多地区的下三叠统不缺失,与冈底斯三叠纪在整体上处于海洋沉积区的观点一致,隆格尔隆起并不存在。根据近年来积累的西藏地区下三叠统的地层资料,指出冈底斯西部早三叠世为大面积的白云岩蒸发岩台地相和局部碳酸盐岩台内坳陷相间的古地理格局。The increasingly discovered Triassic marine sedimentary data become the main reason to deduce that the paleogeographic model of the Gangdise during Triassic should be a sea rather than a land.However,some geologists still insist that the southern Gangdise block was in an uplifting background,marked as the Longar–Gongbujiangda terrestrial magmatic arc during Early Triassic.This opinion mainly comes from the absent Triassic strata.The Renduo section is located within the Longar uplifting zone,where no Triassic strata were found in the previous research.Through detailed conodont biostratigraphic work,the authors obtained typical Early Triassic conodont specimens assigned into the genus“Pachycladina”from the strata originally ascribed to be the Middle Permian Xiala Formation.So it could be ensured that the Lower Triassic strata were not absent from the study section,but were characterized by dolomite.Regionally,the Lower Triassic dolomite could be correlative to the upper part of the Mujiuco Formation.This finding shows that the lower Triassic strata were well developed in the Rendo area,which quite coincides with the view that the Gangdise during Triassic was in marine depositional setting,and so the Longar uplift viewpoint for Triassic is questionable.Depending on the Lower Triassic sections,the authors depict a litho-paleogeographic pattern showing that two facies could be recognizable in the west Gangdise of the Early Triassic.They are respectively the dolomitic evaporation platform facies and the carbonate platform depression facies.The former is obviously predominant in the spatial distribution.

关 键 词：西藏 冈底斯 仁多 木纠错组 早三叠世 牙形石 古地理格局 

分 类 号：P534.51[天文地球—古生物学与地层学] P531[天文地球—地质学]