Abstract: The Mesozoic-Cenozoic Simao Basin is an important salt-bearing basin in Southwestern Yunnan, Southwestern China.
There is controversy on the origin of the salts from the Simao Basin. In this paper, we analyzed the Sr isotope characteristics of the salt
in different salt-bearing zones from the Simao Basin, to shed insights into the source of the salts. Sr isotopic (87Sr/86Sr) ratios of drill core
samples in Mohei vary from 0.708598 to 0.709333, which are consistent with the 87Sr/86Sr ratio of the salt rocks (0.707504 to 0.711069)
reported from other parts of the Simao Basin. Such range of 87Sr/86Sr ratio is consistent with that of Mesozoic-Cenozoic seawater (i.e.,
0.7068-0.7092). Based on Sr isotope evidence, in combination with the geological evolution history of the basin, geochemical and
mineral characteristics, we propose that the Mesozoic-Cenozoic salt in the Simao Basin is mainly of marine origin, but a small
proportion of terrigenous materials were delivered to basins via rivers during the evaporite-forming events.

Key words: Simao Basin, salt-bearing basin, salt rocks, value of 87Sr/86Sr ratio