Coupling of tectonic uplift and climate change as influences on drainage evolution: A case study at the NE margin of the Tibetan Plateau

Abstract

In tectonically active regions, surface uplift is generally considered to be an important cause of drainage evolution, but the effect of climate change on this process has not been fully evaluated. In this study, we conducted a provenance analysis of Minghai (MH) drill-core sediments from the foreland basin (i.e., the Jiudong Basin) of the Zoulang Nan Shan (the central part of the northern Qilian Shan). We aimed to reconstruct the fluvial evolution of the basin and to determine the role of tectonic activity and climate change in the evolutionary process. Provenance analyses indicate the existence of two changes in drainage pattern since 7.0 Ma that are closely linked to the thrusting process of the North Qilian Shan fault system. During the first (∼4.5 Ma) change, the in-sequence thrusting induced rapid uplift of the Yumu Shan in the frontal area of the Zoulang Nan Shan, which caused diversion of the rivers flowing through the Yumu Shan. During the second change (∼2.75 Ma), the thrusting of the North Qilian Shan fault caused intense uplift of the Zoulang Nan Shan, resulting in the capture by transverse rivers in its northern slope of rivers within the mountain range. Additionally, aridification at ∼4.5 Ma and climatic cooling at ∼2.75 Ma affected the evolution of the rivers. The aridification at ∼4.5 Ma resulted in reduced runoff, erosion, and fluvial incision rate, and facilitated the first change in the drainage pattern. The climatic cooling at ∼2.75 Ma induced rapid erosion in the upper reaches of the rivers and enlarged the erosion rate contrast between the south and north side of the Zoulang Nan Shan, both of which facilitated the second change in the drainage pattern. Overall, our study reflects the combined effects of tectonic uplift and climate change on the drainage evolution process.