中国北方宁南盆地古近纪晚期咸化湖盆演化及其区域地质意义  

Late Paleogene Saline Lake Evolution of the Ningnan Basin,Northern China,and its Regional Geological Significance

作　　者：吴小力[1] 李荣西[1] 胡建民[2] 程敬华[1] 赵帮胜 刘福田[1] 李得路[1] 覃小丽[1] 李佳佳[1] 刘博彪 

机构地区：[1]长安大学地球科学与资源学院,西安710054 [2]中国地质科学院地质力学研究所,北京100081

出　　处：《地质学报》2017年第4期954-967,共14页Acta Geologica Sinica

基　　金：国家自然基金项目(编号:41173055);中央高校基本科研业务费专项资金(编号:310827172101)联合资助的成果

摘　　要：本文以宁南盆地北部的贺家口子清水营组剖面为研究目标,对古近纪晚期清水营组的岩性特征、石膏主元素地球化学特征和泥岩有机地球化学特征进行研究,结果表明:清水营组岩性以灰绿-紫红色泥岩、石膏及二者互层为主,可划分为8个二级沉积旋回和3个一级沉积旋回。石膏中CaO含量反映了咸化湖盆中石膏的化学沉积作用,Al_2O_3等为陆源碎屑来源,清水营组下段为盐湖深水环境沉积的纯净石膏;中段石膏沉积的水体较浅。清水营组下段地层泥岩TOC和生烃潜量(S_1+S_2)较高,说明在咸化湖盆演化早期气候较湿润、水体较深;而泥岩降解潜力相对小,反映有机质以高等植物来源为主,陆源输入较多。在此研究基础上,认为宁南盆地清水营组沉积包括:蒸发岩的沉积和碎屑岩的沉积;咸化湖盆演化尚未达到钾盐等盐岩沉淀的高浓缩阶段。咸化湖盆演化主要经历了早期封闭深水盐湖发育阶段、中期封闭浅水盐湖鼎盛阶段和晚期开阔浅水盐湖消亡阶段。宁南盆地古近纪晚期咸化湖盆演化与盆地的持续构造沉降和各次级沉积坳陷最终连为统一的湖泊这一重大区域沉积事件有明显的响应关系。With the Hejiakouzi stratigraphic section of Qingshuiying Formation in the northern Ningnan basin chosen as the research target,this study carried out research of the lithology of Qingshuiying Formation,major element features of gypsum,and organic geochemical parameters of mudstone.The results show that lithology of Qingshuiying Formation is dominated by intercalated gray-green and purple mudstone and gypsum.The Qingshuiying Formation can be divided into eight secondary depositional cycles and three primary cycles.CaO content of gypsum reflects chemical deposition of gypsum in saline lake basin,with Al_2O_3 from terrigenous clastic sedimentation.The lower segment of the Qingshuiyin Formation is gypsum deposited in deep water of saline lake and the gypsum in middle segment was deposited in shallow water;mudstone in the lower part of the Qingshuiyin Formation contains high TOC and hydrocarbon potential（S1＋S2）,indicating that climate was relatively humid and water was deep at early stage of saline lake evolution.Besides the decreasing degradation potential,organic matter was derived mainly from high plant sources,most of which were from land.The study shows that the Qingshuiying Formation in the Ningnan basin resulted from sedimentation of both evaporite and terrigenous clastic rock.But the evolution of saline lake did not reach the high evaporation stage at which halite（such as sylvine）can be precipitated.The Late Paleogene evolution of saline lake can be divided into early closed deep saline lake,middle closed shallow saline lake and late open shallow saline lake stages,and was good response to the continuing tectonic subsidence and the regional sedimentary event that all secondary sedimentary depressions developed into a unified lake.

关 键 词：咸化湖盆 蒸发岩 石膏 古近纪晚期 宁南盆地 

分 类 号：P534.61[天文地球—古生物学与地层学]