Trace element characteristics of sediments in Jianghan Basin：Implications for expansion of the upper reaches of the Yangtze River

Abstract：The Jianghan Basin is the largest basin after the Yangtze River flows through the Three Gorges. Sediments of more than 300 m thick have been deposited in the basin since 2.77 Ma B.P. They are mainly composed of fluvial and lacustrine deposits. Meanwhile, there are also several sedimentary cycles. In order to find out the provenance change of the sediments, the authors studied the trace elements in the samples collected from ZL borehole by using the ICP-MS. The dispersion extent of the trace element compositions of these samples has become less with the decrease of the depth since Pliocene, and tended to be close to the mean value of the upper crust. This suggests that the drainage area has become larger. Values of ∑REE, Y, Th, U and ratios of Th/Sc, Co/Th, La/Sc, Cr/Cu become smaller, suggesting that modern Yangtze River was probably formed after 1.25 Ma B.P.