Provenance evidence for the early-to-middle Pleistocene drainage reorganization of the Songhua River, NE China

Abstract

The Songhua River, one of seven major water systems in China, is the most famous river in Northeast China. However, it is still unclear whether the paleo-Songhua River had a reversed flow direction in the geological past and what mechanisms controlled changes in the flow direction. This study presents new results utilizing detrital zircon U-Pb geochronology and heavy mineral composition retrieved from a well-dated 102-m sediment core and from fluvial sediments in the Songhua River drainage basin, to reveal the evolution of the river system. A shift in Precambrian (>600 Ma) and 100–400 Ma age spectra can be observed at 62.2 m (∼0.94 Ma) in the core, and the heavy mineral composition also shows remarkable variations above and below 62.2 m. Provenance analysis shows that the sediments above 62.2 m in the core originated from the west (i.e., from the direction of the Songnen Plain), but below 62.2 m were fed from areas in the east (i.e., from the direction of the Jia-Yi divide), indicating that the paleo-Songhua River flowed westwards into the Songnen Plain before 0.94 Ma. A conceptual model is therefore proposed for the Songhua River drainage evolution over the early-to-middle Pleistocene. The westward-flowing paleo-Songhua River was captured by the eastward-flowing paleo-Sanjiang River at the Jia-Yi divide due to headward erosion of the paleo-Sanjiang River, leading to the initiation of a unified eastward flowing river system at ∼ 0.94 Ma. The second reorganization of the Songnen river system occurred at 0.46 Ma, characterized by the termination of the Songnen paleolake and the disintegration of the centripetal river system. The tectonics and climate were the main drivers controlling the evolution processes of the paleo-Songhua River before 1.2 Ma and after 0.94 Ma, respectively, whereas they acted together during 1.2–0.94 Ma. The tectonic uplifting of the Songliao divide and the long-term aridification in the Songnen Plain collectively controlled the second drainage reorganization in the Songnen Plain at 0.46 Ma.