西藏白垩纪中期Orbitolinids(有孔虫)的分布与古地理意义  

Distribution of Mid-Cretaceous Orbitolinids in Xizang (Tibet) and Its Paleobiogeographic Implications

作　　者：万晓樵[1] 吴雁华[1] 李国彪[1] 

机构地区：[1]中国地质大学岩石圈构造,深部过程与探测技术实验室,北京100083

出　　处：《地质学报》2003年第1期1-8,共8页Acta Geologica Sinica

基　　金：国家重点基础研究发展规划项目(编号G1998040800);中国地质调查局地质调查项目(编号 20001300009111)资助的成果

摘　　要：白垩纪中期Orbitolinids在全球许多地区均有分布,其生存地区以环特提斯洋的滨浅海地带为主,当时它沿这一滨浅海区广泛扩散。在拉萨地块,该动物群大量分布于冈底斯南缘弧前盆地、冈底斯—念青唐古拉弧内盆地和藏北弧背盆地。沿拉萨地块这一构造单元向东西两侧的延续地段,Orbitolinids发育于缅甸中一东部的Central Cenozoic带和Shan-Tanintharyi地块,以及克什米尔Ladakh一带。该动物群向北穿越班公湖—怒江缝合带往羌塘盆地扩散。受东特提斯洋的阻隔,其分布范围向南没有跨越印度河—雅鲁藏布江缝合带。印度板块当时可能已与非洲大陆分离并向北漂移,该动物群也没能从非洲大陆东侧越过海洋进入印度大陆。据Orbitolinids、介形虫和双壳类的分布,识别出以印度河—雅鲁藏布江缝合带为界的两个生物地理分区。Orbitolinids is a kind of larger foraminifera. It occurred frequently during late Barremian to Cenomanian of Cretaceous and distributed worldwide, especially in the shallow marine belts surrounding the Tethys ocean. Its distribution in Xizang (Tibet) is limited in the Lhasa Block and some parts of the Qiangtang Basin. To both sides of this area, the distribution extends to Myanmar in the east and Ladakh to the west. Along the coast of Tethys, it migrated to Japan, Malaysia, Indonesia, Kashmir, Afghanistan, Mid-East, West and South Europe, North Africa and Caribbean regions. It never migrated into the Indian Plate where a mixed planktonic and smaller benthic foraminiferal fauna appeared during that time. Orbitolinids was found in the Tanganyika region in east Africa, but it did not migrate eastward into the Indian Plate either. Like Orbitolinids, a bivalve fauna of Isodomella-Caestocorbula found in the Lhasa Block belongs to the Japanese-East Asia sub-province (Wen, 1992), and no affinity has been found from the Indian continent. Whatley and Bajpai (2000) described an ostracod fauna of Limnocythere falsocarinata-Frambocythere tumiensis-Gomphocythere gomphiomatos. The fauna is shown to be an endemic Indian fauna without links to the specific level with China or Mongolia. The distribution of Orbitolinids and relative biotas support the tectonic geography. It is firmly established that the rise of the Tibetan plateau is the result of convergence of different terranes. During mid-Cretaceous, the Lhasa block had attached to the Eurasian continent. The Bangong Lake-Nujiang River suture closed at the end of Jurassic. By that time the Lhasa block was at the south margin of the Eurasian continent, thus the shallow water faunas like Orbitolinids and bivalves could migrate along the east and west margin of the Eurasian continent. Paleonbiogeographically, the Lhasa Block belongs to the north temperate realm. The Indian Plate started to move away from Africa by early Cretaceous and drifted to the north. It was isolated from Eu

关 键 词：西藏 白垩纪 Orbitolinids 大陆漂移 古地理 介形虫 双壳类 

分 类 号：Q915[天文地球—古生物学与地层学]