Eocene fossil carbonate microfacies and sedimentary environment in Gangba-Tingri, southern Tibet

Abstract: The Youngest marine strata are exposed in the Gamba-Tingri area, southern Tibet. The study of this succession of marine strata may provide good information about the late evolutional history and closing age of the Tibet-Tethys remnant sea. On the basis of detailed fieldwork and laboratory thin-section identification, the authors studied the fossil carbonate microfacies of the Eocene Zhepure Formation in the Gamba-Tingri area. Ten types of microfacies (MF1-MF10) and five types of biofacies are recognized. The genetic mechanism of conglomeratic limestone of the Zhepure Formation is also discussed in this paper. It is suggested that the conglomeratic limestone formed completely by contour current sediments on the platform-margin marine slope, rather than by redistribution of materials. Based on the above study, a detailed analysis is made on the late phase of the sedimentary evolution of Tibet-Tethys. The authors consider that a transgression took place in the Gamba-Tingri basin during the Eocene Ypresian-early Lutetian. In the late Lutetian, the Gamba-Tingri area was generally in a regressive environment. At that time, however, the Gamba area became a restricted deep-water depression as a consequence of continental compression due to plate collision. In the early Priabonian seawater completely withdrew from this area.