Sedimentary stages and indications of potassium formation in Late Cretaceous Tuylock Formation in Shache(Yarkand)Depression——Evidence from fluid inclusions of halite
Objectives;The composition of fluid inclusions of halite records the composition information of brine in ancient salt lake,which can reveal whether brine concentration reaches the stage of potassium salt deposition and predict potassium formation in salt lake.The Shache(Yarkand)Depression in Xinjiang is located in the southwest of Tarim Basin.The upper part of Tuylock Formation developed at the end of Late Cretaceous is a lens of rock salt with a maximum known pure salt thickness of 264 m,which is considered to be a favorable horizon for searching for potassium.In recent years,fluid inclusions in most ancient evaporite basins in China have been obtained and predicted for potassium formation,but the inclusions in Shache Depression have not been tested.Methods:In this paper,the fluid inclusions in halite at Kalatale salt point and Tashimilike salt point in Shache Depression were measured by inductively coupled plasma mass spectrometry.Results:The results show that the average Br～content of Kalatale salt point and Tashimilike salt point is 65.50 mg/L and 243.95 mg/L,respectively.The Mg2+/Ca2+ratios were 0.43 and 0.32,respectively,reflecting that the Late Cretaceous palaeosalt lake deposits in the basin were deposited during the"calcite sea"period of geological history.The mean bromo—chlorine coefficients were 0.11 and 0.39,respectively.It is revealed that the Late Cretaceous ancient salt lake brine evolution in Shache Depression reached the potassium salt deposition stage in the Tashimilike salt point area.Conclusions:The area where the Tashimilike salt point is located has a good potassium formation prospect,which is of great significance for the delineation of the potassium salt metallogenic target area in this basin and the study of the ancient salt lake brine evolution.
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