New evidence for the incision history of the Liuchong River, Southwest China, from cosmogenic 26Al/10Be burial ages in cave sediments

Cosmogenic nuclides 10Be and 26Al have been analyzed for sediments from the multilevel riverside caves along the Liuchong River at the southeastern margin of the Tibetan Plateau. The Liuchong River is the northern origin of Wujiang River, which passes through the northwestern Guizhou Plateau and cuts down hundreds of meters into the bedrock, leaving behind an abundance of multilevel caves. The measured 26Al/10Be ratios produced the apparent burial ages in range of 0.49-2.85 Ma. Taking into account of geomorphic and geological backgrounds, the Dashi Cave located at the highest level along the Liuchong River system formed around 0.75 Ma ago, which probably suggests the initial formation age of the modern Wujiang River. The resulted incision rate of ∼480 m/Ma in Guizhou in the last 0.75 Ma is slightly higher than those in adjacent areas. This feature implies an intensive downcutting history of the Liuchong River during the Quaternary, which might be primarily caused by the uplift of Tibetan Plateau, cut-through of the Three Gorges and soluble carbonate bedrock.