Geochemical characteristics of elements in the Paleogene Yunlong Formation and the restoration of paleoenvironment in Lanping basin

In order to restore the sedimentary environment of the Paleogene Yunlong Formation in the Lanping basin, inductively coupled plasma mass spectrometry(ICP-MS) was used to analyze trace elements in 13 samples of gypsum, limestone, gypsum mud, mudstone and sandstone from the Paleogene Yunlong Formation in Lanping Basin. The sedimentary environments and paleoclimate are estimated based on the spider diagram of trace elements in each lithology and the characteristics of the ratio of Cu/Zn, Sr/Cu and Sr/Ba and the content of Sr. The results show that:gypsum, limestone, gypsum mud, mudstone and sandstone are all rich in Rb, Pb, Zr; gypsum and gypsum mud were formed in the dry and hot marine salt water in an lean oxygen and weak reduction environment; sandstone and mudstone were formed in oxygen-rich oxidation environment of warm and humid continental freshwater; limestone was formed in the oxygen-rich oxidation environment of dry and hot marine saline water. Based on this, the evolution model of sedimentary environment in the study area was established and divided into two stages. The first stage was the deposition of weakly-reduced marine saltwater lake with dry climate, and gypsum, limestone and gypsum mud were deposited. The second stage was a warm and humid oxygen-rich oxidation environment, where sandstone and mudstone were deposited. This change in sedimentary environment is closely related to the cyclical changes of the climate and environment in the Yunlong period, also provides a basis for the exploration of mineral resources in the basin.