ZENG Yong-yao¹, WANG Jian-she², ZHANG Wei³

(1. LanZhou Resources & Environment Voc-Tech College, Lanzhou 730600, China;
2.Institute of Tibetan Plateau Research, Chinese of Academy of Sciences, Beijing 100101, China; 3. University of Chinese Academy of Sciences, Beijing 100049, China)

Abstract: The Qiangtang Basin is an evaporite basin with prospective evaporite resource. Researches on the gypsum bed of the Jurassic Xiali Formation in the Yanshiping profile and K- and Na-bearing salty springs in the Qiangtang Basin indicate that the Xiali Formation is a very important targeting bed for prospecting sodium and potassium salt resources in the Qiangtang basin. Obviously, the Xiali Formation of the Jurassic Yanshiping Group is an important layer to evaluate the potential of evaporates formation in the Qiangtang Basin. We measured the B, Sr and Ba from the sediments in the Xiali Formation of Yanshiping Section, Qiangtang Basin and then calculated paleo-salinities of the Xiali Formation. Our conclusion is: the change of paleo-salinities in the Xiali Formation of Yanshiping Section during 164－160.2 Ma can be generally divided into three stages. The first stage（0－260 m、164－162.3 Ma）in the lower part of the Xiali Formation could be in a freshwater environment. While the second stage（260－500 m、162.3－160.7 Ma）in the middle part of the Xiali Formation could be a brackish water environment and the third stage（500－608 m, 160.7－160.2 Ma）in the upper part of the Xiali Formation could be a salt water environment. In addition, the upper part of the Xiali Formation is a valuable layer to explore for halite deposit and may be potentially valuable in the future exploration for potash deposits in the basin, which is revealed by analyzing the conditions of provenance, climate and tectonism. And the correlation coefficient of Ca2+ - SO42-, Na+ - Cl？, K+ - Cl？ in the area clearly demonstrated that, the upper part of the Xiali Formation was an optimum stratum for hilate formation superior to potash formation in the Qiangtang Basin.

Keywords: Paleosalinity; Middle-Late Jurassic; Xiali Formation; Qiangtang Basin

ACTA MINERALOGICA SINICA Vol. 39, No.5, 2019, page 539-548