8th International Nannoplankton Association Conference


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Yulin Xu, Shaozhi Mao:
Cretaceous-Early Tertiary calcareous nannofossils from southern Tibet and the closing time of E Tethys in Tibet, China

Marine Cretaceous-Early Tertiary strata are exposed extensively in S Tibet and in the Gandies Mountain of SW Tibet, China. Samples containing calcareous nannofossils were collected from four sections, namely the Gongzha and Qumiba sections of Dingri County, and the Zongshan and Zongpu sections of Gamba County. Nine calcareous nannofossil zones or assemblages are established, based on the first or last appearance datums (FAD or LAD) of some marker-species. They are: 1. Rucinolithus irregularis/Rhagodiscus angustus Biozone; 2. Prediscosphaera columnata/Eiffellithus turriseiffelii Assemblage Zone; 3. Microrhabdulus decoratus/Cretarhabdus crenulatus Assemblage Zone; 4. Eiffellithus eximius/Micula decussata Assemblage Zone; 5. Lucianorhabdus cayeuxii/Quadrum gothicum Assemblage Zone; 6. Arkhangelskiella cymbiformis/Quadrum sissinghii Assemblage Zone; 7. Nannotetrina fulgens/Chiasmolithus gigas Biozone; 8. Discoaster bifax/Chiasmolithus solitus Biozone; and 9. Sphenolithus pseudoradians/Reticulofenestra umbilica Biozone. These nannofossil zones, or assemblage zones, belong to biozones CC7 to CC25 of Sissingh's and NP15-17 of Okada & Bukry's biozonations.

The ninth nannofossil zone is dated as late Middle Eocene, and the strata yielding this zone is the highest marine bed in Tibet. These facts show that the sea-water did not withdraw from the Qinghai-Xizang (Tibet) Plateau until around 38Ma, based on new data. The E Tethys closed in Tibet during late Middle Eocene, resulting in the dramatic rise above sea-level of the Qinghai-Xizang (Tibet) Plateau.


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 [Division of Micropalaeontology] [Department of Geosciences] [Bremen University]

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