Composition of middle-late Eocene salt lakes in the Jintan Basin of eastern China: Evidence of marine transgressions

Abstract

Abundant continental salt deposits were formed in salt basins in eastern China around the Cretaceous–Tertiary periods. However, whether these evaporites had a marine or non-marine origin remains controversial. The Jintan Basin is located between South China and North China, and has a series of very thick, relatively pure salt deposits, such that data from the salt deposits in the Jintan Basin could provide new evidence of marine transgression. The large scale of these salt deposits implies the supplies of marine transgression. Primary fluid inclusions in the halite deposits of the Jintan Basin have recorded the composition of the evaporated salt lake water. The Br contents in halite range from 2 to 16 ppm, and clearly higher than inland non-marine salt deposits in the Yunying Depression, Jianghan Basin, South China. The δ37Cl values of marine salt deposits across different geological eras range from −1 to +1‰. The δ37Cl values from halite in the Jintan Basin range from −0.66 to +0.23‰ (close to zero), indicating a possible marine origin. Our analyses from fluid inclusions in halite show K varies from 0.7 to 15.8 g/l; Mg from 1.1 to 3.1 g/l; sulfate-ion from 3.7 to 27.7 g/l in the samples. The composition of fluid inclusions in halite, from a sample in the lower part of the halite section in the Jintan Basin is very similar to marine seawater on Jänecke diagram. The δ34S of anhydrite deposits (+26.32‰ to +26.51‰) are also very similar to contemporary seawater. Thus, the evidence indicates the Jintan Basin was supplied sporadically by marine transgressions.