Seawater retreated from the Tethyan Himalaya of south Tibet at ca. 49 Ma, not ca. 34 Ma

Abstract Timing of seawater retreat from the Tethyan Himalaya is of great importance, as it provides a minimum age control on the initial India-Asia collision. In south Tibet, however, it is still in dispute, with suggested ages ranging from >50 Ma to ca. 34 Ma. Here we present data of (1) larger benthic foraminifera from the topmost Zongpu Formation; (2) planktonic foraminifera; and (3) detrital zircon U-Pb ages from the Youxia and Shenkeza Formations at Guru, Tingri, and Gamba, with a special emphasis on the poorly studied Guru area. At Guru, existence of the Shallow Benthic Zonation (SBZ) 7 Zone index fossils of Alveolina moussoulensis Hottinger and Al. laxa Hottinger constrains the initial deposition of the Youxia Formation at ca. 54 Ma. Coexistence of the youngest planktonic foraminifera Acarinina boudreauxi Fleisher, Ac. coalingensis (Cushman and Hanna), and Ac. bullbrooki (Bolli) from the Youxia and Shenkeza Formations indicates their final deposition at ca. 49 Ma (E 7 Zone, where E stands for Eocene Planktonic foraminiferal Zone). Zircon U-Pb data are generally similar, with the youngest age peak of ca. 68–50 Ma resulting from input of the Gangdese Arc volcanic detritus. The complete lack of <49 Ma data among >1000 accepted ages implies that marine deposition probably ceased at ca. 49 Ma, consistent with the planktonic foraminiferal result. Integrating with previous results, we conclude that seawater retreated from both south Tibet and Zanskar at ca. 49 Ma. The initial collision happened quasi-simultaneously in the western and eastern Tethyan Himalaya, before ca. 49 Ma. Our findings do not support either a younger collisional age or a diachronous collisional process from the west to the east.