The Cenozoic Sedimentary Record in Qaidam Basin and Its Implications for Tectonic Evolution of the Northern Tibetan Plateau

Key words: 
• Tibetan Plateau /
• Qaidam Basin /
• tectonic uplift /
• sedimentary record /
• basin-range coupling

Abstract: The tectonic events and climatic changes during the formation and evolution of the Tibetan Plateau could be recorded in the sedimentary succession in adjacent basins. Qaidam Basin, which is located in the northern sector of Tibetan Plateau, preserves a set of thick and continuous Cenozoic sediments. These sediments are the reliable materials for investigation on tectonic  evolution of the Tibetan Plateau. Here, we present an integrated study of the Cenozoic sediments from outcrops and drilling well cores. The results indicate that  Qaidam Basin has recorded three phases of tectonic evolution. The details can be described as follows. (1) The red coarse detrital sediments of Lulehe Formation which are characterized by low abundances of (Zircon, Tourmaline Rutile) minerals and low heavy mineral stability index. These sediments recorded an event of orogenic movement and tectonic uplift in the whole basin scale, which can be explained as the farfield effects of India-Eurasia collision. Furthermore, after this orogenic event, the region of Altyn and East Kunlun areas was rapidly denudated and flattened, and then became to depositional areas since Middle-Late Eocene. Therefore, it is concluded that Qaidam, Tarim and Hoh Xil Basins may have been parts of a single topographic depression at that time. (2) The Shang Ganchaigou Formation and Xia Youshashan Formation coarse sediments in front of the Altyn Mountains formed in response to the uplift of the Altyn area, whereas the dominated fine-grain sediments with high heavy mineral stability index of other vegions of the Qaiclam Basin  can be interpreted as delta-lake facies, suggesting a stage of quiet tectonic background. This quiet setting can be caused by the large-amplitude lateral extrusion along the sinistral strike-slip Altyn Tagh Fault which accommodated the continuing indentation of India into Eurasia. (3) The Shang Youshashan Formation and Shizigou Formation upward-coarsening sediments with low heavy mineral stability index were deposited in high-gradient depositional systems. These sediments recorded the event of crustal shortening and thickening and the intense, rapid uplift of the whole northern Tibetan Plateau. Furthermore, the integrated provenance analysis results indicate the Cenozoic source compositions for the Northern  Qaidam Basin did not have significant changes over time.