From deep-sea to high mountain ranges:: palaeogeographic and biotic changes in Hohxil, the source area of the Yangtze River (Tibet Plateau) since the Late Palaeozoic

Lithological and especially palacontological data allow reconstruction of the palaeogeographic history of Hohxil, the source area of the Yangtze River in the northern Tibet Plateau, since the Late Palaeozoic. Early Carboniferous - Early Permian deep water environments, part of the Palaeotethys, were replaced by a Late Permian shelf sea following convergence of the Qiangtang and Kunlun blocks. During the Triassic, a varied facies pattern existed with open shelf to deep sea sediments in the north and non-marine to marginally marine environments in the south. Renewed compression between the Qiangtang and Kunlun blocks at the end of the Triassic led to formation of a mountain range. Subsequently, it was only during the Middle Jurassic that, due to renewed transgression, a shallow shelf sea extended into the southern parts of Hohxil. Collision of the Lhasa block with the Qiangtang block at the end of the Jurassic caused the final retreat of the sea from the area. From the Cretaceous throughout most of the Tertiary, lacustrine and fluvial sedimentation prevailed, with a distinct sedimentary gap during the Paleocene and Eocene due to collision of the Indian and Eurasian plates. Pliocene events include volcanic eruptions and strong uplift, the latter continuing to the present day, resulting in an average altitude of the area of more than 5,000 in; this extremely elevated region became the source of the Yangtze River.