羌塘盆地中晚侏罗世雁石坪剖面夏里组古盐度与成盐意义

The Paleosalinity of the Middle-Late Jurassic Xiali Formation in the Yanshiping Section, Qiangtang Basin and its significance for salification

羌塘盆地是一个具有成盐远景的蒸发岩盆地,对羌塘盆地侏罗系雁石坪群夏里组出露的石膏层和具有钾、钠异常的盐泉水研究表明,夏里组是羌塘盆地潜在的形成钠盐、钾盐的目标层位之一。本文通过对羌塘盆地雁石坪剖面夏里组硼元素、锶元素和钡元素的测量,计算Adams古盐度和Sr/Ba比值,来恢复雁石坪剖面夏里组的古盐度。根据Sr/Ba比值、Adams古盐度和Walker相当硼含量的变化趋势,雁石坪剖面夏里组古盐度可以划分为以下3个阶段:夏里组下段(0~260 m、164~162.3 Ma)淡水环境、中段(260~500 m、162.3~160.7 Ma)咸水环境和上段(500~608 m、160.7~160.2 Ma)超咸水环境。另外,通过分析物源、气候以及古地理条件,认为夏里组具备适宜成盐的物源、气候和古地理条件,根据夏里组上段Ca^2+-SO4^2-离子、Na^+-Cl^-离子和K^+-Cl^-离子的相关性分析表明,夏里组上段古环境已经演化到沉积硫酸盐阶段或者沉积氯化物早期阶段,即夏里组上段形成石盐的环境要优于形成钾盐的环境。

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 Ca^2+-SO4^2-, 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.