The Youngest Marine Deposits Preserved In Southern Tibet And Disappearance Of The Tethyan Ocean

The convergence and collision of Indian and Eurasian plates is the most significant tectonic events during the Cenozoic. It is closely related with the disappearance of the Tethyan Ocean in Himalayan region. Numerous works have been done by different researchers, trying to reconstruct the collision progress, especially to date the timing of the collision. But the results vary from different study locations and different methods. The upmost marine deposit is one of the most direct evidence for the disappearance of the Tethyan Ocean, and it has long been used to constrain the timing of the collision. In Himalayan region, however, the age of the upmost marine deposit is still controversial.In this study, we choose the Gamba-Tingri region in southern Tibet as the study area. Three sections have been studied, which are Zongpu section(in Gamba), Qumiba section(in Tingri) and Yadong section. Through the division and correlation of the Paleogene sequence, Zongpubei Formation has been regarded as the upmost marine deposit in the Gamba-Tingri region. By reassessment of the larger benthic foraminiferal fauna in the underlying Zhepure and Zongpu formations, the bottom of the Zongpubei Formation is assigned to the end of Lutetian. Moreover, the biostratigraphic analysis of planktonic foraminifera, benthic foraminifera and calcareous nannofossils indicates the range of Zongpubei Formation is from Bartonian to Priabonian.Regional correlation has been done throughout the Himalayan regions, including Kohat, Zanskar in the western part and Siang, Bengal basin in the eastern. The result shows that marine condition widely spread in Himalayan region indicating the existence of a Tethyan seaway during the Paleogene period. The Eocene larger benthic foraminiferal fauna in different areas of Himalaya shows high similarity which demonstrates they probably share the same habitat.The shallow marine condition in Himalayan regions did not change until the late Lutetian, indicating those areas were not close enough to the trench to undergo any subsidence. In fact, it seems likely that the marine conditions did not entirely disappear by the Priabonian, especially in the eastern Himalaya. Notably this remains a maximum age estimate for the disappearance of the Tethyan Ocean, thus the Indian-Eurasian continental collision, as most sections are truncated by erosion or faulting.