Liu, Y.; Yang, Y.; Yang, R.; Galy, A.; Jin, Z.; Fang, X.; Song, B.
Gondwana Research, 2023, 118, 76-91
Voir en ligne : https://doi.org/10.1016/j.gr.2023.02.012
Abstract :
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 systems 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 ∼ 54 Ma. Most of the interval remains a higher 87Sr/86Sr ratio of ∼ 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 ∼ 44.5 – ∼32 Ma and after ∼ 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 ∼ 44.5 – ∼32 Ma and at southeast of the basin after ∼ 16 Ma, suggesting a southeastward migration of the basin depocenter that was mainly caused by tectonic uplift with a subordinate 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.