Initial India-Asia Continental Collision and Foreland Basin Evolution in the Tethyan Himalaya of Tibet: Evidence from Stratigraphy and Paleontology

The onset of the India-Asia continent-continent collision in Tibet was accompanied by the elimination of oceanic crust and the development of a peripheral foreland basin on the subducting continental crust. However, owing to the progressively southward migration of this foreland basin, the appearance of flexural uplift (forebulge) predated flexural subsidence (foredeep) at the distal location, such as at Gamba and Tingri in the southern Tethyan Himalaya. Consequently, to trace and date this forebulge may provide a better constraint on the India-Asia collision. At Gamba and Tingri, our studies on the stratigraphy, paleontology, and paleoenvironment show that depositional cessation of the limestones occurred at Shallow Benthic Zone 7 (SBZ 7, similar to 54-55 Ma) in the Gamba area and at the base of SBZ 10 (similar to 52.8 Ma) in the Tingri area. At Gamba, a conglomerate layer within the upper Zongpu Formation is suggested to represent the formation of the forebulge at the onset of the foreland basin, and the coincidence of the conglomerate layer with the Carbon Isotope Excursion (CIE) provides a precise age of similar to 56 Ma (the Paleocene/Eocene boundary) for the possible initial India-Asia continental collision. Our results not only provide a reliable and precise age for the India-Asia collision but, for the first time, report time equivalence between the India-Asia collision and the CIE in Tibet.