银川盆地清水营组咸化湖盆沉积特征与湖盆演化

Sedimentary Characteristics and Lake Basin Evolution of Salinized Lake Basin of Qingshuiying Formation in Yinchuan Basin

银川盆地发育厚层新生界,其中清水营组是咸化湖盆发育的时期,也是烃源岩最为发育的层段,因此明确清水营组的沉积特征及湖盆演化具有重要的地质意义和勘探意义.综合利用野外露头、钻井岩心、测井及有机地球化学资料,对银川盆地古近纪晚期清水营组的岩性、岩相类型进行分析总结,明确沉积环境.利用岩电特征、小波变换对清水营组进行沉积旋回识别与划分,在此基础上分析湖盆演化.清水营组岩性主要为灰色泥岩、棕红色泥岩、含石膏泥岩、石膏及薄层细砂岩、粉砂岩等,共有四种岩相组合类型.清水营组可划分3个四级旋回,对应清水营组咸化湖盆的3个演化阶段:SQ1为裂陷初期咸化湖盆的发育阶段;SQ2为强烈裂陷期,湖盆水体深度有所增大,盐湖鼎盛阶段;SQ3期水体变浅,湖盆范围变大,封闭性减弱,由咸水湖演化成淡水湖.

Thick Cenozoic strata are developed in the Yinchuan Basin,among which the Qingshuiying Formation is the period of salinized lake basin development and the most developed layer of hydrocarbon source rocks.Therefore,it is of great geological significance and exploration significance to clarify the sedimentary characteristics and lake basin evolution of the Qingshuiying Formation.In this paper,the lithology and petrographic types of the Late Paleoproterozoic Qingshuiying Formation in the Yinchuan Basin are analyzed and summarized using field outcrops,drill cores,logs and organic geochemical data to clarify the depositional environment.The sedimentary cyclogenesis of the Qingshuiying Formation was identified and classified using rockelectric characteristics and wavelet transform,and the evolution of the lake basin was analyzed on this basis.The lithology of the Qingshuiying Formation is mainly gray mudstone,brown-red mudstone,gypsum-bearing mudstone,gypsum and thin-bedded fine sandstone and siltstone,etc.,and there are four types of petrographic assemblages.The Qingshuiying Formation can be divided into three four-order sedimentary cycles,corresponding to the three evolutionary stages of the salinized lake basin of the Qingshuiying Formation.SQ1is the development stage of the salinized lake basin at the early stage of rifting.SQ2is the period of strong rifting,in which the depth of the water body of the lake basin has increased,and the salinized lake is at its peak stage.SQ3is the period when the water body becomes shallow,in which the scope of the lake basin becomes larger,the closure weakens,and the saline lake evolves into a freshwater lake.