The Cenozoic intramontane GongheGuide Basin in Qinghai Province, China, is tectonically controlled by the sinistral strikeslip framework of the Kunlun and Altyn Tagh-South Qilian faults in the northeastern Tibetan Plateau. The basin is fi lled with thick Cenozoic clastic sedimentary formations, which provide important evidence of the deformation of this part of the plateau, although they have long lacked good age constraints. Detailed magnetostratigraphic and paleontologic investigations of fi ve sections in the Guide Basin and their lithologic and sedimentary characteristics allow us to divide a formerly undifferentiated unit (the Guide Group) into six formations (where ages are now magnetostratigraphically well established, they are given in parentheses): the Amigang (1.8-2.6 Ma), Ganjia (2.6-3.6 Ma), and Herjia formations (3.6 to ca. 7.0-7.8 Ma), and the older Miocene Ashigong, Garang, and Guidemen formations. These rocks document a generally upward coarsening sequence, characterized by increasing accumulation rates. Increasing gravel content and sizes of its components, changes of bedding dips and source rock types, and marginal growth faults collectively refl ect accelerated deformation and uplift of the NE Tibetan Plateau after 8 Ma, punctuated by a sharp increase in sedimentation rate at ca. 3.2 Ma that refl ects the boulder conglomerates of the Ganjia formation. Interestingly, much of the vergence of the compressional deformation in the basin is to the south, accommodated by a sequence of six thrusts (F1-F6), which become active one by one progressively later toward the south, undoubtedly contributing to the uplift of this part of the plateau. F1 likely initiated the Guide Basin due to crustal fl exure in the Oligocene, F2 was active in the early Miocene, F4 and F5 at ca. 3.6 Ma, and F6 was active in the early Pleistocene. The detailed late Miocene and younger magnetostratigraphy allows us to place much improved time constraints on the deformation and, hence, uplift of northeastern Tibet, which, when compared with ages for events on other parts of the plateau, provides important boundary conditions for the geodynamical evolution of Tibet.

The way in which the NE Tibetan Plateau uplifted and its impact on climatic change are crucial to understanding the evolution of the Tibetan Plateau and the development of the present geomorphology and climate of Central and East Asia. This paper is not a comprehensive review of current thinking but instead synthesises our past decades of work together with a number of new findings. The dating of Late Cenozoic basin sediments and the tectonic geomorphology of the NE Tibetan Plateau demonstrates that the rapid persistent rise of this plateau began ~8 ± 1 Ma followed by stepwise accelerated rise at ~3.6 Ma, 2.6 Ma, 1.8–1.7 Ma, 1.2–0.6 Ma and 0.15 Ma. The Yellow River basin developed at ~1.7 Ma and evolved to its present pattern through stepwise backward-expansion toward its source area in response to the stepwise uplift of the plateau. High-resolution multi-climatic proxy records from the basins and terrace sediments indicate a persistent stepwise accelerated enhancement of the East Asian winter monsoon and drying of the Asian interior coupled with the episodic tectonic uplift since ~8 Ma and later also with the global cooling since ~3.2 Ma, suggesting a major role for tectonic forcing of the cooling.

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[1] Lake sediments are important archives of paleoclimate change and erosion history. A 938.5 m long core (SG-1) of lacustrine sediments, dated at 2.77 Ma to 0.1 Ma, was obtained from the western Qaidam Basin in the northeastern Tibetan Plateau, consisting of dark grayish mudstone and grayish siltstone, intercalated with salts and fine sandstones in the upper part. Magnetic susceptibility data, combined with detailed rock magnetic properties, were analyzed for revealing the significance of ferro(i)magnetic concentration for past changes of climate and erosion. Mass-specific susceptibility (c) shows a striking cyclic and long-term variation. Samples with high c values are dominated by magnetite and maghemite with pseudo-single-domain properties. In contrast, samples with low c values contain maghemite from single-domain to multidomain and, additionally, a significant fraction of hematite. The driving mechanism of c variation can be explained by three alternative models: (1) different source regions with alternations of wind and cryoclastic erosion in a wider hinterland (dry-cold climate) and surface runoff erosion from a narrower area (more humid climate) and (2 and 3) low-temperature oxidation, occurring either in the lake sediments (dry climate) or in the catchment area during weathering (more humid climate). Trends of c match with changes in sedimention rates and are roughly synchronous with the deep-sea d18 O record on a glacial-interglacial timescale. Therefore, the concentration of magnetic minerals in the western Qaidam Basin sediments is likely controlled by both tectonic influence and paleoenvironmental changes but can be best interpreted by alternations and trends of dry-cold and more humid periods due to Asian drying and global cooling.