Foraminiferal And Their Responses To OAE In Gamba-Tingri,Southern Tibet

Cretaceous is a period with frequent occurrence of significant geological events,such as sea level rise,ocean anoxic events,ocean red bed,mass biological extinction at the end of Cretaceous,and large igneous province.Previous studies have shown that the oceanic anoxic events are widely distributed in space and time.The Cretaceous oceanic anoxic events mainly include OAE1(Aptian-Albian boundary),OAE2(Cenomanian-Turonian boundary),and OAE3(Coniacian-Santonian boundary).Continuous marine cretaceous strata are distributed in southern Tibet,which contain abundant foraminifera fossils.A detailed study of the foraminifera biostratigraphic study on the Zongshan and Gongzha sections in Gamba-Tingri area was carried out and the following conclusions were obtained in this thesis:(1)a large number of foraminiferal fossils were obtained from the shale and limestone of the Zongshan and Gongzha sections,and a total of 58 species of 11 foraminiferal genera were identified.In the Zongshan section,three fossil zones were divided as Rotalipora cushmani,Whiteinella archaeocretacea,and Helvetoglobotruncana helvetica zones,giving an age of time to Cenomanian-Turonian.In Gongzha section three fossil zones divided as Dicarinella asymetrica,Globotruncana ventricosa,and Globotruncanita calcarata zones,giving an age of Santonian-Campanian.(2)based on the analysis of the foraminifera biozones in the Zongshan section,the boundary between the Rotalipora cushmani zone and Helvetoglobotruncana helvetica zone is considered to be the C/T boundary.The gongzha section foraminifera with comprehensive analysis,think Globotruncana ventricosa,Globotruncanita calcarata between two fossil zone to Campanian and Turonian boundary.In the Gongzha section,the Campanian/Turonian boundary is suggested to be located between Globotruncana ventricosa zone and Globotruncanita calcarata zone.(3)During the Late Cretaceosu,the southern Tibet area also experienced the oceanic anoxic event,and the evolution of foraminifera in this stage was also affected by the oceanic anoxic event,and experienced extinction,survival and recovery.