Deciphering source-to-sink history from a solute perspective: A Sr isotope approach in the Qaidam Basin, NE Tibet

Sediment source-to-sink history is pivotal to investigating the evolution of ancient sedimentary basin. Previous study focuses mostly on reconstruction of various components of siliciclastic sedimentary sys-tems from initial source areas through the dispersal system to deposition areas, but less on the dissolved load that displays distinct transport and deposition dynamics. Here we take the Qaidam Basin (NE Tibet) as a case to provide a solute perspective for deciphering the source-to-sink history of an intracontinental basin. The modern observations exhibit a remarkable contrast of the solute Sr isotopic regime with the northern sources (the Qilian Shan) with high 87Sr/86Sr ratios and the southern sources with low 87Sr/86Sr ratios. The paleowater solute 87Sr/86Sr ratios in the northern basin fluctuate between 0.711 and 0.715 since ti 54 Ma. Most of the interval remains a higher 87Sr/86Sr ratio of ti 0.713, indicating that the solute Sr was supplied solely by the Qilian Shan. But two periods of low 87Sr/86Sr ratio (0.711-0.712) at ti 44.5 -ti32 Ma and after ti 16 Ma suggest that there may be two paleo-megalakes connecting the northern and southern sources, and the solute with low 87Sr/86Sr ratio from the southern sources can thus approach the northern basin via lake water mixing. The two low 87Sr/86Sr paleo-megalakes developed at the northwest of the basin at ti 44.5 -ti32 Ma and at southeast of the basin after ti 16 Ma, suggesting a southeastward migration of the basin depocenter that was mainly caused by tectonic uplift with a sub-ordinate impact of climate-induced lake expansion. Our results show a more complex and dynamic solute transport routing history in a large basin than that indicated by coarse clastic provenance studies, and suggest that such a solute Sr approach can be useful to trace sediment routing linked to denudation of high-grade metamorphic rocks and hydrological connections under drainage reorganization.(c) 2023 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.

Automated summary

Using the Qaidam Basin as a case study, this research reveals the source-to-sink history of a basin by focusing on dissolved load. The study finds significant differences in the 87Sr/86Sr ratio of dissolved solutes between the northern and southern parts of the basin, suggesting the presence of two ancient megafloods that linked the two regions. The results highlight the complex transport history of dissolved load and its role in sediment routing.