Age Of The Disconformity In The Late Cretaceous Strata Of Tingri Area, South Tibet

Cretaceous and Paleogene are the most important converge time between the Eurasian and India plates. The upper Cretaceous sedimentary series of the Tingri and Gangba areas (Tethys Himalayas) represent the depositional history of the Indian passive continental margin before the collision. In this series of strata, planktonic foraminifera were preserved very well, which are the criteria of the stratigraphy. Therefore, a detailed study of planktonic foraminiferal biostratigraphy in this strata may provide useful imformation of collision.In this study,6stratigraphic sections (Gelamu, Gongzha, Shenkeza, Dazhuba, Gubao and Baima Sections) from Tingri, Gangba, Tuna areas were measured in detail in the field. A disconformity was discovered in the late Cretaceous strata between the Jiubao Formation and the overlying Zhepureshanpo Formation in the Tingri area. In totle,47species of14genera (Abathomphalus, Archaeoglobigerina, Contusotruncana, Dicarinella, Gansserina, Globigerinelloides, Globotruncana, Globotruncanita, Hedbergella, Heterohelix, Laeviheterohelix, Marginotruncana, Radotruncana, Venrilabrella) were identified and described in the thesis.In the foraminiferal biostratigraphic studies,4lists of biozones from Campanian to Maastrichtian were recognized at the first time in Tingri area, which could be compared with the biozones in the global low latitude areas. They are "D. concavata D. asymetrica-Gna. aegyptiaca-Gan. gansseri" in the Gelamu Section,"D. concavata-D. asymetrica-Gna. aegyptiaca-Gan. gansseri-Ab. mayaroensis " in the Gongzha Section,"D. concavata-D. asymetrica-Gna. ventricosa-R. calcarata" in the Shenkeza Section,"D. concavata-D. asymetrica-Gna. aegyptiaca-Ab. mayaroensis" in the Dazhuba Section.The age of the disconformity can be constrained by the planktonic foraminiferal biozone. Dicarinella asymetrica Zone and Globotruncana aegyptiaca Zone were recognized in the upper part of the Jiubao Formation and the lowest part of Zhepureshanpo Formation respectively which indicated the age of the two formation are Santonian and late Campanian. The strata ranged from early to late Campanian (approximately9Ma) were missing. The cause of this disconformity may be the turbidite in Tingri area based on the analysis of sedimentary characteristics.