Late Cretaceous proto-type basin in the western Qinling: Background of Cenozoic uplifting of Tibet Plateau
Guo Jinjing1, Han Wenfeng1, Zhao Haitao1, Li Xuefeng1, Zhang Fanyu2
1. School of Geology and Geomatics, Tianjin Chengjian University, Tianjin 300384;
2. College of Civil Engineering and Mechanics, Lanzhou University, Lanzhou 730000
Abstract：
The Qinghai-Tibet Plateau is a large and high elevation tectonic relief having uplifted since Cenozoic. Its temporal and spatial uplifting processes is one of many key issues in research on the Qinghai-Tibet Plateau. By studying on the Upper Cretaceous red bed strata in the western Qinling, this article attempts to restore Late Cretaceous prototype basin and its reflecting relief features of western Qinling, the northern margin of the Qinghai-Tibet Plateau. This study will provide constrain on essentially starting background before the Cenozoic uplift of the Qinghai-Tibet Plateau. There are a set of Late Cretaceous red bed strata in Minxian-Wushan area, West Qinling Mountains. These red bed strata overlaid on different-aged strata separated by angular unconformities, having a similar sedimentary sequence. These strata are presently dispersed, being considered as different intermontane basins or strike-slipping pull-part basins during intracontinental tectonic processes. The observations and comparisons on the unconformities between these red bed strata and their underlying strata from different outcrops and various altitudes and the study on grain size distributions and microscopic features of clastic particles, show that the cemented sands of conglomerates and red sandstones over the unconformity has similar characteristics to a desert dune deposition, which may mean ever existence of an arid desert environment in the West Qinling Mountains. It is well known that appearance of desert environment requires not only the hot and arid climate conditions, but also need relatively flat topography in spatial conditions. Therefore, it is suggested that the present-day West Qinling Mountains was ancient relatively-flatted topographic landform at the beginning of the Late Cretaceous. In addition, Upper Cretaceous red bed strata in West Qinling Mountains, at present, distributed discontinuously on the relatively-flatted top surface. The bottom is characterized by conglomerates and sandstones interbedded with desert sediments and the upper is mainly composed of red mudstones, siltstones and fine sandstones in river-lacustrine facies fine clastic sediments. Based upon above data, this paper speculates that the West Qinling Mountains was broad-range river topographic relief at the Early Late Cretaceous and evolving into the flat-like geomorphology of lacustrine basin at the end of Late Cretaceous. The proto-type basin should be wholly one wide lacustrine basin. The present dispersed distribution of Upper Cretaceous disconformities and red beds resulted from regional differentiated uplift of the crust and erosion during Cenozoic Tibetan Plateau rising, thrusting, strike-slipping due to India-Eurasia plate collision. Relatively-flatted topographic relief of the West Qinling Mountains in Late Cretaceous provides important clues and reference for understanding the spreading of Tibetan Plateau uplifting and intraplate deformation in its northeast margin.
. Late Cretaceous proto-type basin in the western Qinling: Background of Cenozoic uplifting of Tibet Plateau[J]. Chinese Journal of Geology, 2015, 50(2): 364-376.
2015, Vol. 50 
