新疆莎车盆地上白垩统-古近系蒸发岩沉积及成钾前景

新疆莎车盆地发育大范围的蒸发岩。蒸发岩沉积与海侵-海退密切相关,自晚白垩世—渐新世以来,莎车盆地至少有5次小规模海侵-海退旋回,除阿尔塔什组石膏岩为断续海侵期沉积外,其余基本为海退期沉积。莎车盆地主要的蒸发岩沉积层位为吐依洛克组上段及阿尔塔什组。野外调查显示,吐依洛克组石盐岩露头主要沿西昆仑山前呈长条状分布,基本呈透镜体,阿尔塔什组石膏岩露头则见于盆地大部分地区,包括西昆仑山前、南天山山前及麦盖提斜坡,横向上持续稳定。野外调查及室内分析显示,盐类矿物主要为石盐、石膏、硬石膏,少量杂卤石、钙芒硝及钾石膏。盆地中石盐岩透镜体在横向上的不连续性,可能反应了吐依洛克组沉积晚期西昆仑山前存在多个次级古盐湖凹地,在干旱条件下浓缩成盐,而次级古盐湖在演化过程中大范围巨厚石膏岩的缺失,可能与当时的海退时间极短有关。依据莎车盆地蒸发岩沉积特征、盐类矿物组合、古盐湖演化环境,推测盆地有利的成钾层位为吐依洛克组上段,在乌帕尔一带发现成钾显示,可能为有利的成钾区域;而盆地小范围、厚度不大的石盐沉积及埋藏深度大为不利的找钾因素。

Evaporite deposition and potassium enrichment prospect from Upper Cretaceous to Paleogene in Yarkand Basin, Xinjiang

A wide range of evaporite deposits have been developed since late Cretaceous-Oligocene in Yarkand Basin, Xinjiang. The deposition of evaporites had a closely relationship with transgression-regression, and there developed at least five times of small transgression-regression cycles in this period. The Aertashi Formation gypsum rocks were continuous transgression sedimentation while the other strata were essentially regression sedimentation. Evaporite sedimentary layers are mainly in the upper member of Tuilok Formation and Aertashi Formation. Field work shows that rock salt outcrops are distributed in long stripe form along the foreland of West Kunlun Mountains and are characterized by lenticular sedimentation. However, the gypsum outcrops are distributed steadily laterally in most parts of the basin such as the foreland of West Kunlun Mountains, South Tianshan Mountains and Maigaiti Slope. Laboratory analysis shows that the primary saline minerals are halite, gypsum, and anhydrite, with minor polyhalite, glauberite and syngenite. The lateral discontinuity of rock salt lens may imply that there might have existed more secondary ancient salt lake depressions in the foreland of West Kunlun Mountains in late sedimentation period of Tuilok Formation, during which materials were concentrated into salt under the condition of drought, and the lack of large scale thick gypsum rock in the evolutionary process might have been related to the very short time of regression in that period. According to the evaporite sedimentary characteristics, salt mineral assemblage and the ancient salt lake evolution environment in Yarkand Basin, the authors conclude that the favorable potassium horizon is the upper member of Tuilok Formation, and the Wupaer area is probably the favorable potash-forming place, as shown by some clues. Nevertheless, the small thin rock salt deposition and large depth are unfavorable factors.