The relationship between tectonism and desertification inferred from the provenance and lithofacies changes of the Cenozoic terrestrial sequence of the southwestern Tarim basin

Abstract

The Tarim basin is one of the most arid areas in the world and its major part is occupied by the Taklimakan desert. Although unraveling the history of aridification of Taklimakan desert is important to understand the global climate change during the Cenozoic, the timing and the mechanism of its formation are still controversial. One of the hypotheses is that the uplift of the Pamir locating to the west of the Tarim basin blocked the intrusion of the moist air and induced the aridification in the Tarim basin. In this study, we explored the linkage between the uplift of the Pamir and the desertification in the Tarim basin during the period from the late Eocene to the middle Miocene. Provenance changes of the fluvial deposits along the Aertashi section, which is located in the southwestern edge of the Tarim basin and offers the longest record with the reliable age model, was examined using Electron Spin Resonance (ESR) signal intensity and crystallinity index (CI) of quartz in the sand fraction of fluvial sandstone and the thin section observation to identify the timings of tectonic events in the Pamir from which clastic materials were supplied by rivers. Our results suggest that major provenance changes in the drainage of the river delivering the clasts to the Aertashi section occurred at ca. 26 Ma, 20 Ma, and 15 Ma. These timings are mostly consistent with the timings observed in the previous provenance studies in the Aertashi section and probably reflect tectonic events in the Pamir. On the other hand, the Tarim basin was under the relatively arid condition after ca. 34 Ma based on the first occurrence of sand dune deposit. Hence, our result does not support the hypothesis that the onset of the aridification in the Tarim basin was caused by the uplift of the Pamir and consequent shut down of the moisture supply from the Paratethys Sea although the afterward intensification of tectonic events in the Pamir might be related to the phased uplift.