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The Barkol Basin (BB) is an intramontane basin in the easternmost Tian Shan, Northwest China. We reconstructed the tectonic evolution of the BB based on an investigation of its stratigraphy and faults, and we differentiated the basin infill into Quaternary sediments and the Oligocene–Miocene Taoshuyuanzi Formation by combining field observations and geophysical data with borehole data. We used detrital zircon U–Pb dating and palaeo-currents to decipher the provenance of the lower Jurassic Badaowan Formation, which contains the only Mesozoic sediments throughout the easternmost Tian Shan. The results demonstrate that the BB and Harlik Range constitute the main sources. Furthermore, we found that the Taoshuyuanzi Formation unconformably overlies the Palaeozoic basement in the basin, indicating that the BB formed during the Oligocene–Miocene. Based on Magnetotelluric (MT) and seismic profiles, this formation was deposited under the control of basin-bounded faults. According to the field investigation, the boundary faults of the basin were recognized as sinistral strike-slip normal faults. Additionally, remote sensing and electron spin resonance (ESR) data provided valuable information on the Quaternary proluvial fan divisions, which suggest a multi-stage tectonic evolution of the basin during the Quaternary. The Mesozoic–Cenozoic basin evolution in the easternmost Tian Shan was divided into four phases based on an integrated analysis of the stratigraphy and structures of the Santanghu Basin and the Turpan-Hami Basin: (1) from the Late Triassic to the Early-Middle Jurassic, tectonic subsidence dominated the Santanghu Basin and Turpan-Hami Basin; (2) during the Late Jurassic-Eocene, the episodic uplift of the Tian Shan Mountains constricted the Turpan-Hami Basin and the Santanghu Basin; (3) during the Oligocene–Miocene, the BB formed as a subsidence basin controlled by sinistral strike-slip normal faults, and the basins filled with thick layers of clastic rocks; and (4) during the Pliocene–Quaternary, the eastern BB uplifted, and the basins deformed. In conjunction with previous research, the dynamic background of the formation of the BB was presumably related to the clockwise rotation of the Tarim Block to the south and the strong left-lateral movement of the Gobi-Tian Shan fault system.

The northeastern Tibetan Plateau is located at the convergence of the Asian winter and summer monsoons and westerlies; thus, this area has witnessed historic climate changes. The Xunhua basin is an intermontane basin on the northeastern margin of the Tibetan Plateau. The basin contains more than 2000 m of Cenozoic fluvial–lacustrine sediments, recording a long history of climate and environmental changes. We collected the mid-Miocene sediments from the Xunhua basin and used palynological methods to discuss the relationship between aridification in the interior of Asia, global cooling, and uplift of the Tibetan Plateau. Based on the palynological analysis of the Xigou section, Xunhua basin, the palynological diagram is subdivided into three pollen zones and past vegetation and climate are reconstructed. Zone I, Ephedripites–Nitraridites–Chenopodipollis–Quercoidites (14.0–12.5 Ma), represents mixed shrub–steppe vegetation with a dry and cold climate. In zone II, Pinaceae–Betulaepollenites–Ephedripites–Chenopodipollis–Graminidites (12.5–8.0 Ma), the vegetation and climate conditions improved, even though the vegetation was still dominated by shrub–steppe taxa. Zone III, Ephedripites–Nitrariadites–Chenopodipollis (8.0–5.0 Ma), represents desert steppe vegetation with drier and colder climate. The palynological records suggest that shrub–steppe dominated the whole Xigou section and the content gradually increased, implying a protracted aridification process, although there was an obvious climate improvement during 12.5–8.0 Ma. The aridification in the Xunhua basin and surrounding mountains during 14.0–12.5 Ma was probably related to global cooling induced by the rapid expansion of the East Antarctic ice-sheets and the relatively higher evaporation rate. During the 12.5–8.0 Ma period, although topographic changes (uplift of Jishi Shan) decreased precipitation and strengthened aridification in the Xunhua basin on leeward slopes, the improved vegetation and climate conditions were probably controlled by the decrease in evaporation rates as a result of continuous cooling. From 8.0 to 5.0 Ma, the rapid development of the desert steppe can be attributed to global cooling and uplift of the Tibetan Plateau.

Through a comprehensive study of magnetostratigraphy and sedimentology of several basins in the northeastern Tibetan Plateau, we reveal that the study area mainly experienced six tectonic uplift stages at approximately 52 Ma, 34–30 Ma, 24–20 Ma, 16–12 Ma, 8–6 Ma, and 3.6–2.6 Ma. Comprehensive analyses of pollen assemblages from the Qaidam, Linxia, Xining, and West Jiuquan Basins show that the northeastern Tibetan Plateau has undergone six major changes in vegetation types and climate: 50–40 Ma for the warm-humid forest vegetation, 40–23 Ma for the warm-arid and temperate-arid forest steppe vegetation, 23–18.6 Ma for the warm-humid and temperate-humid forest vegetation, 18.6–8.5 Ma for the warm-humid and cool-humid forest steppe vegetation, 8.6–5 Ma for the temperate sub-humid savanna steppe vegetation, and 5–1.8 Ma for the cold-arid steppe vegetation. Comprehensive comparisons of tectonic uplift events inferred from sedimentary records, climatic changes inferred from pollen, and global climate changes show that in the northeastern Tibetan Plateau the climate in the Paleogene at low altitude was mainly controlled by the global climate change, while that in the Neogene interval with high altitude landscapes of mountains and basins is more controlled by altitude and morphology.

The timing of onset of deposition of the Lulehe Formation is a significant factor in understanding the genesis of the Qaidam basin and the evolution of the Tibetan Plateau. Here, we describe a detailed magnetostratigraphic and magnetic fabric study of the middle and lower parts of the Lulehe Formation. A total of 234 samples were collected from 117 sites throughout a thickness of almost 460 m of fluvial and lacustrine deposits at the Xitieshan section in the northeastern Qaidam basin. Out of these sites, 94 sites yielded well-defined characteristic remanent magnetization components by stepwise thermal demagnetization and were used to establish the magnetostratigraphy of the studied section. Based on correlation with the geomagnetic polarity timescale, the studied section spans the period from 53.8 Ma to 50.7 Ma. Our results show a three-fold decrease in sedimentation rates as well as marked change in facies from braided river to delta and shore–shallow lake around 52.6 Ma, which suggests tectonic uplift of the northeastern Qaidam basin margin ridge was rapid at the onset of formation of the Qaidam basin and subsequently weakened after 52.6 Ma. The anisotropy of magnetic susceptibility results indicate that tectonic compression stress had reached the northeastern Tibetan Plateau by the early stages of Indo–Eurasian plate collision and that the direction of stress in the study area was NE–SW. Furthermore, a weakening of tectonic compression stress around 52.6 Ma is consistent with sedimentary records. The age of initial deposition of the Qaidam basin (around 53.8 Ma) was almost synchronous with that of the Qiangtang, Hoh Xil, Xining, and Lanzhou basins, which implies that stress was transferred rapidly through the Tibetan Plateau during or immediately after the onset of Indo–Eurasian collision.

We have studied the evolution of the tectonic lithofacies paleogeography of Paleocene–Eocene, Oligocene, Miocene, and Pliocene of the Qinghai–Tibet Plateau by compiling data regarding the type, tectonic setting, and lithostratigraphic sequence of 98 remnant basins in the plateau area. Our results can be summarized as follows. (1) The Paleocene to Eocene is characterized by uplift and erosion in the Songpan–Garze and Gangdise belts, depression (lakes and pluvial plains) in eastern Tarim, Qaidam, Qiangtang, and Hoh Xil, and the Neo-Tethys Sea in the western and southern Qinghai–Tibet Plateau. (2) The Oligocene is characterized by uplift in the Gangdise–Himalaya and Karakorum regions (marked by the absence of sedimentation), fluvial transport (originating eastward and flowing westward) in the Brahmaputra region (marked by the deposition of Dazhuka conglomerate), uplift and erosion in western Kunlun and Songpan-Garze, and depression (lakes) in the Tarim, Qaidam, Qiangtang, and Hoh Xil. The Oligocene is further characterized by depressional littoral and neritic basins in southwestern Tarim, with marine facies deposition ceasing at the end of the Oligocene. (3) For the Miocene, a widespread regional unconformity (ca. 23 Ma) in and adjacent to the plateau indicates comprehensive uplift of the plateau. This period is characterized by depressions (lakes) in the Tarim, Qaidam, Xining–Nanzhou, Qiangtang, and Hoh Xil. Lacustrine facies deposition expanded to peak in and adjacent to the plateau ca. 18–13 Ma, and north–south fault basins formed in southern Tibet ca. 13–10 Ma. All of these features indicate that the plateau uplifted to its peak and began to collapse. (4) Uplift and erosion occurred during the Pliocene in most parts of the plateau, except in the Hoh Xil–Qiangtang, Tarim, and Qaidam. The continuous uplift and intensive taphrogeny in the plateau divided the original large basin into small basins, deposition of lacustrine facies decreased considerably, and boulderstone accumulated, indicating a response to the overall uplift of the plateau. Here, we discuss the evolution of tectonic lithofacies paleogeography in Cenozoic and its response to the tectonic uplift of the Qinghai-Tibet Plateau in relation to the above characteristics. We have recognized five major uplift events, which occurred during 58–53 Ma, 45–30 Ma, 25–20 Ma, 13–7 Ma, and since 5 Ma. The results presented here indicate that the paleogeomorphic configurations of the Qinghai–Tibet Plateau turned over during the late Miocene, with high elevations in the east during the pre-Miocene switching to high contours in the west at the end of Miocene.