Paleosalinity evolution of the Paleogene perennial Qaidam lake on the Tibetan Plateau: climatic vs. tectonic control

As the largest Cenozoic terrestrial intermountain basin in the Tibetan Plateau, the Qaidam Basin is an ideal basin to understand the coupling controls of tectonics and climate on plateau lake evolution. More than 10,000 data of chloride content from the Paleogene sediments of the endorheic Qaidam Basin have been collected to monitor changes in lake paleosalinity. Results show that there were two prominent salinity increase events in the Paleogene paleolake, one in the late Eocene (~ 40 Ma) and the other in the transition from the Eocene to Oligocene (EOT, ~ 35.5 Ma). The first salinity increase event was evidenced by the expansion of saline water, the connection of two previous separated saline centers and the deposition of thick-bedded halite in a local sag, which correlated with the late Eocene’s frequently fluctuated climate. The other salinity increase event at the EOT was characterized by the expansion of mesosaline water range, which corresponded well to the drier condition of the Oligocene icehouse climate. The synchronous migration of the saline centers and depocenters demonstrates that the Qaidam Basin was a tectonically active saline basin, where the activity of main faults controlled the occurrence and disappearance of supersaline center under the overall brackish background. The deposition of over 200-m thick-bedded halite during the late Eocene in a local sag was the result of coupled effects by active tectonics and fluctuated climate.