Origin of Late Quaternary Gravel and Drainage Basin Expansion in the Northern Chinese Tian Shan: Insights From Sediment Provenance Analyses

The source-to-sink relationship between a sedimentary basin and its adjacent mountain range is vital for understanding the genesis of piedmont coarse-grained sediments and the evolution of mountain topography. By integrating zircon U-Pb dating and heavy mineral assemblage analyses on 15 samples, this work focuses on the change of the provenance with time in the Urumqi River Neogene-Pleistocene continental sequence in the northern Chinese Tian Shan foreland, which has been chronologically constrained to range from ∼6.8 to ∼0.55 Ma. The results of the integrated provenance analyses reveal two shifts in provenance during the periods of 4.6–2.5 and 0.9–0.55 Ma, yielding new zircon U-Pb age signals from the glacier-covered headwaters of the Urumqi River. These two identified provenance adjustments are causally related to enhanced glacial erosion in the high mountain. We propose that enhanced glacial erosion could have caused southward expansion of the Urumqi River drainage basin, increased production of coarse-grained materials with new zircon U-Pb age signals, and finally accumulation of piedmont alluvial gravel. The observed topographic and sedimentary responses to enhanced glaciation could have been common phenomena during the late Quaternary in alpine areas, where a large number of alluvial fans are widely distributed like aprons along the mountain front, as seen in the piedmonts of the Tian Shan in the arid interior of Asia.