Cadmium and clay mineral analysis of late Pliocene–Pleistocene deposits from Jianghan Basin, central China: Implications for sedimentary provenance and evolution of the Yangtze River

Abstract

The Tibetan Plateau uplift, triggered by India–Eurasia collision, is strongly associated with the evolution of the Yangtze River. The evolution of the river is of great significance for understanding the geomorphology of modern Asian landforms and exploring the response of river development to tectonic uplift and monsoon evolution. Although numerous methods have been employed to reconstruct the evolutionary history of the Yangtze River, a century old debate still persists over its age, especially for that of the Three Gorges, the estimated age of which ranges from Late Cretaceous to Late Pleistocene. In this study, provenance of the Late Cenozoic deposits from the Jianghan Basin were determined based on the Cadmium (Cd) and clay mineral contents, to constrain the age of the Three Gorges. Previous studies have reported marked Cd anomalies detected in the Jianghan Basin, Yangtze River system, which were concluded to be dominantly a result of natural factors rather than anthropogenic activities. We identified two units (0–160 m and 160–300 m depth) from samples collected from the Zhoulao (ZL) core, obtained from the depocenter of the Jianghan Basin. The distinctly higher Cd levels from 160 m to the top of the core indicate the input of sediments from above the Three Gorges, especially the Jinsha River catchment. Additionally, three sections were diagnosed on the basis of variations in clay mineral contents and their corresponding formation mechanisms were demonstrated. Sections 1 and 2 derived sediments from proximal materials within the Jianghan Basin and the variations therein were coupled with climatic changes whereas, the sediments in section 3 were found to be prominently controlled by provenance superior to climate change, with materials derived from the upper Yangtze River; these results are consistent with the reported changes in Cd levels. We interpret this change in sediment provenance at 160 m depth resulted from the incision of the Three Gorges, which brought sediments from the Yangtze. The previously obtained paleomagnetic data demonstrate that the boundary at 160 m represents the end of the Olduvai Subchron (1.945–1.778 Ma), meaning that the incision of the Three Gorges valley occurred no later than 1.778 Ma.