Eocene seawater retreat from the southwest Tarim Basin and implications for early Cenozoic tectonic evolution in the Pamir Plateau

Abstract

The Pamir Plateau lies in the western end of the India–Eurasia collision zone, being an unusual example for studying crustal shortening and evolution of the Neotethys Ocean. Here we present new results from the southwestern margin of the Tarim Basin for discussing tectonic history in the northern Pamir Plateau as well as for providing precise dates of the final seawater retreat from the studied region. Our results indicate that early uplift of the northern edge of the Pamir Plateau occurred at about 55Ma, but this uplift preceded the closure of the link between the Neotethys and the Tarim Basin. Five marine transgression and regression cycles occurred during the early Eocene, mostly in response to global eustatic sea level fluctuations, and the final seawater retreat from the southwest Tarim Basin occurred at about 47Ma. Another uplift episode started 34Ma, supported by the accumulation of coarse molasse deposits as well as our palynological evidence, suggesting that the convergence between the Pamir Plateau and the Tian Shan ranges accelerated since the beginning of the early Oligocene.