Genetic relations between Paleogene high bromine rock salt and sylvite in west of Kuqa depression in Xinjiang

The characteristics of high potassium and low bromine in the south, and high bromine and low potassium in the north of the rock salt layers west of Kuqa depression, which is contradicted against the normal evolvement of brine. The purpose of this paper is to explore the genetic relationship between the high bromine rock salt and sylvite in the west Kuqa depression and to guide the prediction of potassium resources. In this paper, the study on stratigraphic correlation, the transgression process of Kuqa depression and the analysis of strontium and sulfur isotope show that the the formation of high bromine rock salt in drill Keshen-208 is earlier than sylvite in drill Yangta-4. Study on protogenetic rock salt cutting inclusion features, inclusion homogenization temperature, main and trace elements, strontium and sulfur isotope characteristics and tectonic background analysis shows that the evolution of drill Yangta-4 was independent and closed in the secondary depression and the brine in the formation stage of high bromine rock salt of drill Keshen-208 was closer to the seawater and evolved in the secondary depression for a long time. The late second salt forming stage of drill Keshen-208 accepted more land-based water, which was in response to the brine evolution stage in the regression period. In general, after entering the Kuqa depression from west to East in the Paleogene, the seawater first went to the north area and then to the south. Yangta area is located at the end of the transgression, which is a terminal secondary depression with shallower brine and long-term closure, becoming the most favorable potassium formation area. At the regression stage, the residual brine converges in the regression channel. At this time, the local depression in the channel (such as the late salt forming stage in Keshen area) is an important favorable area for potassium formation. The Paleogene potash formation in the western section of Kuqa depression generally follows the model of "forming potassium closing the transgressive end and forming potassium in the regression channel depression", which provides a new important idea for the search for potash resources in Kuqa depression.