中-新生代有孔虫古地理对西藏特提斯演变的动态响应  

Dynamic response of Mesozoic Cenozoic foraminiferal paleogeography to the Tibetan Tethys evolution

作　　者：万晓樵[1] WAN Xiaoqiao(State Key Laboratory of Biogeology and Environmental Geology,China University of Geosciences(Beijing),Beijing 100083,China)

机构地区：[1]中国地质大学(北京)生物地质与环境地质国家重点实验室,北京100083

出　　处：《地学前缘》2020年第6期116-127,共12页Earth Science Frontiers

基　　金：国家自然科学基金项目(41790452);中国地质调查局项目(DD20190009)。

摘　　要：有孔虫化石资料是地质历史的真实记录,对不同地质时期古地理格局和生态环境的变迁具有动态响应。西藏特提斯构造带的演化、板块相对地理位置变迁等诸多问题一直是地学界关注的热点。研究西藏特提斯沉积盆地内有孔虫动物群的古生态特征和古地理分布,能够识别生物地理区系,进而恢复不同时期的大地构造演化格局。西藏地区中、新生代古生物地理区系的分化是西藏特提斯地质演变的具体反映。西藏南部早侏罗世产底栖大有孔虫Orbitopsella喜暖动物群,晚侏罗世出现双壳类Buchia喜冷动物群。由此推测,侏罗纪新特提斯洋扩张尤其是中大西洋的开张,将位于印度大陆北缘的特提斯喜马拉雅带,从早侏罗世较低纬度的温暖位置向南推移至较高纬度的低温地区。白垩纪中期Orbitolina有孔虫类群繁盛于特提斯北侧亚洲大陆的拉萨地块和羌塘盆地,但没有出现在印度大陆。这说明当时印度大陆已脱离冈瓦纳大陆向北漂移,受四周深水环境的阻隔,Orbitolina动物群未能向印度大陆扩散。此时深水环境中生活着浮游有孔虫Ticinella Rotalipora动物群。Turonian晚期开始形成海退,拉萨地块的海洋环境基本消失。Coniacian Campanian早期印度大陆北缘浮游有孔虫继续占优势,繁盛Marginotruncana Globotruncana动物群。直至白垩纪末,印度和欧亚大陆之间的深海阻隔仍然存在,雅鲁藏布江缝合带两侧动物群一直存在根本性差异。印度大陆北缘发育着Orbitoides Omphaloceclus动物群,冈底斯南缘则以Lepidorbitoides Pseudorbitoides动物群为特征。古新世Danian期生态环境发生变化,显示大印度与亚洲大陆发生初始碰撞(66~61 Ma)。Selandian期之后,缝合带两侧才出现相同的Miscellanea Daviesina有孔虫类群,生物区系的分异基本结束。始新世早期缝合带两侧为完全相同的生物区系,共同发育底栖大有孔虫Nummulites DiscocyclinaForaminiferal data are the critical record of geological history,they reflect the dynamic changes of geographic patterns and ecologic environments.Various scientific issues,like tectonic evolution and changes of relative positions of plates,are the research topics of geoscientists.Foraminiferal ecology and paleogeographic distribution studies can recognize the peleobiogeographic realms and trace the tectonic evolution.One result of such studies is the recognition that Mesozoic-Cenozoic paleobiogeographic differentiation in Tibet is a dynamic response to the Tibetan-Tethys evolution.In the Early Jurassic,larger benthic foraminifera Orbitopsella and bivalve Lithioties occurred in southern Tibet,both are thermophilic fauna living in the circum-Tethys shallow water.They were dominant during the Pliensbachian to early Toacian.In the Late Jurassic,psychrophilic Buchia biota emerged in southern Tibet.They are identical to the Buchia and Retroceramus found in the Antarctic,south end of South America,New Zealand and Australia.It implies that the opening of Neothetys,especially the Central Atlantic,pushed the Indian Continent southward from lower to higher latitudes.The foraminiferal fossils in the Lower Cretaceous are poorly preserved in Tibet.In the mid-Cretaceous,larger benthic foraminifera Orbitolina widely developed in the Lhasa and Qiangtang basins of the Asian Continent.It occurred frequently in the shallow marine belts surrounding the Tethys Ocean during the late Barremian to Cenomanian of the Cretaceous.Its 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,the Middle East,West and South Europe,North Africa and the Caribbean regions.However,it never migrated into the Indian continent where a mixed planktonic and smaller benthic foraminiferal fauna appeared during that time.Orbitolia was also found in the Tanganyika region in East Africa,but it did not migrate eastward into the Indian continent either.Like Orbitoli

关 键 词：有孔虫古地理 中—新生代 西藏特提斯 演变 

分 类 号：P52[天文地球—古生物学与地层学]