柴达木盆地英西地区下干柴沟组上段高频旋回与古地貌特征

受区域性构造运动和古近纪特殊气候的共同影响，在英西地区沉积了一套陆相咸化湖盆混积岩，其特殊的相序组合对研究陆相咸化湖盆高频层序划分及古地理演化具有重要意义。英西地区下干柴沟组上段地层主要为暗色细粒混积岩，矿物成分复杂，主要由陆源碎屑、碳酸盐矿物和蒸发盐矿物组成，可以划分为碎屑岩、碳酸盐岩和蒸发岩三大岩石类型，分别为湖盆演化的淡化阶段、初始咸化阶段和咸化阶段产物。研究区目的层段识别出7个四级层序（Psq1~Psq7），除Psq1和Psq2不发育区域性盐岩层外，其他四级层序都由碎屑岩段、碳酸盐岩段、混积型蒸发岩段和区域性盐岩层组成，这也反映出气候及湖盆性质的逐渐演化。在四级层序约束下，根据盐岩层相对厚度，对英西地区下干柴沟组上段的古地貌特征进行了恢复。Psq1和Psq2发育于湖盆演化的相对早期阶段，咸水湖范围非常有限。Psq3至Psq5沉积期间，湖水咸化程度逐渐增加，咸水湖范围不断扩大，在几个洼陷区沉积了大套厚层盐岩。Psq6沉积期间，经过前几个阶段的填洼补平，研究区地貌总体趋于平坦，高差幅度明显减小。至Psq7沉积期间，研究区西部逐渐退出深洼区，沉积中心开始向东发生迁移。

High-frequency Cycles and Paleogeomorphic Features of the Upper Member of the Lower Ganchaigou Formation in the Yingxi Area,Qaidam Basin

In the Paleogene,a set of mixed sediments in a salinified-lake basin was developed to the west of the Yingxiong Ridge,controlled by regional tectonic movement and the local climate. The rock series have particular sed-imentary facies successions,which are very important in the study of high-frequency sequence division and paleogeo-graphic evolution of the salinified-lake basin. Upper member strata of the Lower Ganchaigou Formation consist of dark,fine-grained mixed sediments with complex mineral composition,mainly composed of terrigenous clasts,car-bonate minerals and evaporite minerals,which respectively correspond to the pre-salinization stage,the initial salini-zation stage and the final salinization stage of the lake water. In the study area,the strata are divided into seven fourth -order sequences (Psq1-Psq7). Except for Psq1 and Psq2,they occur in three parts:clastic rocks,carbonate rocks and evaporite. Theoretically,deepwater salt forms by the stratification of heavy brine as it sinks. As a result,salt rock in deep depression areas is thicker than in low uplift areas. Therefore,taking into consideration the fourth-order se-quence,the paleogeomorphology of the upper member of the Lower Ganchaigou Formation in the Yingxi area was able to be restored in accordance with the relative thicknesses of the salt rock strata. Psq1and Psq2 developed in the early stages of lake evolution,when the area covered by the salt-water lake was very limited. During the development of Psq3 to Psq5,the degree of salinization gradually increased,and the scope of salt-water lake continually expand-ed,with thick evaporite being formed in the depression area. Then,during the deposition of Psq6,the topography of the study area tended to be flatter due to filling and leveling of the previous stages,and the range of height differences was considerably reduced. Finally, during the deposition of Psq7, the western area of the lake in the study area gradu-ally became shallower and the sedimentary center began to migrate eastward.