Constraining when compressive tectonic stress began to affect the outermost frontier area of the NE Tibetan Plateau is crucial for determining whether the NE Tibetan Plateau was uplifted simultaneously with the India−Asia collision, or whether it underwent progressive northeastward expansion. The subsidence and infilling history of the peripheral basin between the NE Tibetan Plateau and the Beishan Block is the key to resolving this issue. We present the results of lithostratigraphic and magnetostratigraphic analyses from the sedimentary records of a 268-m-long drill core Liangjiazhuang from the Jinta Basin, located in the subsidence area between the tectonically active NE Tibetan Plateau and the relatively stable Beishan Block. Sedimentological and high-resolution magnetostratigraphic analyses show that sedimentation in the Jinta Basin began ca. 3.4 Ma. The sediment accumulation rate increased from 36 mm/k.y. to 114 mm/k.y., accompanied by sedimentary facies changes from braided river at the base to an ephemeral lake at ca. 3.0 Ma, then to a dryland river terminus system at ca. 1.7 Ma, and finally to a braided river again at ca. 1.2 Ma. Initial subsidence of the Jinta Basin began at ca. 3.4 Ma, indicating that the arid denudation plain was disrupted due to the northeastward tectonic propagation of the Tibetan Plateau. The late Pliocene global cooling enhanced the glacial erosion and frost-weathering, and thus supplied a large amount of sediments. Meanwhile, the related isostatic rebound of the Qilian Shan combined with the humid climate drove the long-distance transport of the coarse sediments to the Jinta Basin from ca. 3.4 Ma to 3.0 Ma. Between ca. 3.0 Ma and ca. 1.7 Ma, fine sediments deposited at a high accumulation rate indicates the uplift of the Jintanan Shan and the associated accelerated flexural subsidence of the Jinta Basin. From ca. 1.7 Ma to 0.8 Ma, the progradation of coarse sediments with low sediment accumulation rate indicates the basinward propagation of tectonic stress. The reoccurrence of coarse sediments with a high accumulation rate after ca. 0.8 Ma was forced by the climate oscillations after the mid-Pleistocene transition, which led to the large-scale erosion, transport, and redistribution of the previously deposited clastic materials from the piedmont of the North Qilian Shan and the Jiudong Basin to the downstream Jinta Basin. Consequently, the tectono-geomorphological evolution of the Jinta Basin supports the view of progressive northeastward growth of the Tibetan Plateau and highlights the interplay between tectonic and climatic forcing. Our findings provide a precise chronological framework and detailed records of basin formation and evolution for testing the plateau growth model. They provide a case study of the infilling and evolution of the peripheral basins at the outermost frontier of the NE Tibetan Plateau, as well as of the combined effects of tectonic activity, climate, and surface processes in shaping the regional landforms.
Li et al. (Fri,) studied this question.
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