我国西藏南部海相白垩系含有较丰富的钙质超微化石。文中着重研究岗巴地区两个剖面 (即剖面A ,B)Albian Santonian钙质超微化石的分布。根据标志种的存在 ,识别出 5个初现面事件 ,相应地建立 6个钙质超微化石带 ,自下至上是Prediscosphaera cretacea带 ,Eiffellithus turriseiffeli带 ,Lithraphidites acutum带 ,Gartneragoobliquum带 ,Quadrum gartneri带 ,Lucianorhabdus cayeuxii带。同时 ,通过洲际对比 ,建议以G .obliquum初现面作为划分本区Cenomanian和Turonian界线的标志。此外 ,Q .gartneri带和I .cayeuxii带之间缺失多个化石带 ,据此推测Turonian至Santonian期间本区可能存在沉积间断。

This study deals with calcareous nannofossils of mid-Cretaceous at Gamba Area in Southern Xizang （Tibet）China．The rock samples were collected from the Gamba Group of both Sections A and B．On the basis of the characteristicsediments the Gamba Group can be divided into three stratigraphic units from bottom to top namely the Gambadongshan Chaqiela and Gambacunkou formations．Calcareous nannofossils mainly appeared from the uppermost Gambadongshan Formation to Gambacunkou Formation．The preliminary results enable us to propose a detailed nannofossil zonation for the middleAlbian to the late Santonian．This zonation scheme consists of six zones and five addition biohorizons．The upper part of Gambacunkou Formation clearly exhibits a stratigraphic hiatus since the top of Quadrum gartneri zone （early Turonian） is immediately overlain by Lucianorhabdus cayeuxii zone （late Santonian）．The Cenomanian-Turonian boundary is discussed in detailon the basis of calcareous nannofossil data．The first occurrence of Gartnerago obliquum rather closely corresponds with thefirst appearance datum of Helvetoglobotruncana praehelvetica （foraminifera） thus that they are considered to be very usefulto determine the boundary between Cenomanian and Turonian in Southern Xizang （Tibet）．

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中国科学院古生物与古人类学科基础研究特别支持费(SFPPNo .970702和No .980601)； 国家自然科学基金(No .49872046)资助课题；