【作者】 房建军；

【导师】 刘池阳；

【作者基本信息】 西北大学 ， 矿产普查与勘探， 2009， 博士

【摘要】 宁南盆地主体位于宁夏南部,现今不具盆地形态,为经过后期改造残留的沉积体。展布范围泛指银川盆地之南古近纪-新近纪地层集中广泛出露和分布地区,其主要为大面积红色地层,且分布零星,无固定规律。其地理和大地构造位置重要,东接中生代鄂尔多斯盆地西南缘,与鄂尔多斯地块周缘诸新生代断陷盆地遥相呼应,西接青藏高原东北犄角部位,是青藏高原隆升最直接的响应。因此开展宁南盆地沉积构造演化与后期改造的研究,对探讨鄂尔多斯盆地新生代改造及其区域动力学环境与演变、中生代原盆恢复、该地区进一步油气勘探及青藏高原隆升的环境效应研究,具有重要的、不可替代的意义。目前对于该盆地的形成演化,特别是盆地的后期改造、形成的区域动力学环境和构造属性涉及较少,尚有一系列关键问题有待进一步研究解决。通过野外地质调查与典型剖面观察及实测,基本查清并分析总结了盆地现今古近系-新近系的分布、岩性组合、地层厚度、物源变化、沉积环境演化、前新生界的分布及其与古近系-新近系的接触关系等基本沉积地层特征。认为在寺口子期,盆地由多个相互连通或不连通的小断陷所组成,至清水营期,盆地范围逐步加大,并在红柳沟期发育到鼎盛时期,全区基本上已经为彼此相通或相连的较大型湖盆群,干河沟期盆地北迁,范围缩小。选取固原寺口子剖面,利用磁性地层学研究方法,通过高密度采样和实验测试,结合与本区已有的地层古生物、区域地层和磁性地层学等相关研究的对比分析,综合研究认为宁南盆地的第一套沉积.寺口子组的地层年龄为47.9Ma-29.4Ma B.P.,即寺口子组的地层时代为中始新世-早渐新世,宁南盆地与鄂尔多斯盆地周缘诸新生代断陷盆地的发生具有同步一致性。将古近纪-新近纪地层卷入或构成的断裂、褶皱、不整合接触等地质构造变形作为研究对象,分析了其构造要素、形成时期、变形期次和变形强度等主要构造研究内容,认为盆地现今以≤20km~2的小规模的等轴、开阔-平缓褶皱为主要特征,总体受到南西至北东方向的挤压,与青藏高原的隆升、扩展直接相关。盆地南部的地层接触关系以微角度不整合或和断层接触为主,在盆地中北部,与下伏前新生代地层以超覆接触关系为主。根据对盆地不同地区地震、地质剖面的分析,揭示了在现今,盆地北部新生代地层沉积表现出明显受张性正断层和断陷的控制的结构构造特征,盆地南部新生代地层分布在挤压缩短了的断陷或呈残留的断楔体之中,盆地中部新生代地层的结构构造特征大致介于二者之间。对盆地原始沉积-构造环境的恢复结果,并结合古近系-新近系分布区的地质构造变形特点及后期改造特征,表明现今的盆地面貌是遭受强烈后期改造的结果,改造的基本特征是南早北晚、南强北弱,原始盆地沉积范围明显大于今盆地残留地层沉积展布。在新生代早中期,宁南盆地的沉积作用与鄂尔多斯地块其它同期地堑一样,也是在张性断陷中进行的,彼此形成的区域动力学环境相似。综合上述研究认为,宁南盆地的沉积构造演化历经始新世-渐新世初始断陷、中新世早中期鼎盛时期和中新世晚期分割萎缩三个阶段。在前两个阶段,宁南盆地与鄂尔多斯地块周缘诸断陷盆地的发生、发展有许多相似之处。中新世晚期以来,宁南盆地受到青藏高原隆升扩展的明显渐至强烈的影响,其构造背景由发育时期的拉张逐渐变为挤压,沉积构造演化与诸断陷盆地明显分异,盆地遭受强烈的反转改造而渐趋消亡。更多还原

【Abstract】 The Ningnan Basin Group is the sediment body without basin shape by the late reformation,whichMainly located at the south of Ningxia province.The spread area generally refers to the Tertiary which isMassively uncovered and distributed in the south of the Yin Chuan basin.Most of the strata is red,scattered and ruleless.It has important position for its geography and geotectonics.The residual basin adheres to the southwest of the Mesozoic Ordos basin to the east and the northeastern horn of the Tibet Plateau to the west,which echos the Cenozoic faulted basins in the neighboring area of the Ordos basin at a distance,and is the most immediate response to the uplift of Tibetan plateau.Hence,the study on the formation, evolution and disappear of the Ningnan Basin Group is crucial and irreplaceable to the Cenozoic reformation and the regional geodynamic environment of the Ordos Basin,the recovery of original Mesozoic basin,the oil-gas exploration in this area,as well as the uplift of Tibetan plateau.Many predecessors haveMade exploratory research on the Cenozoic in Ningnan area,but the period they have studied is limited and the work is also relatively simple.The study of the formation,evolution and late reformation of the basin is rarely,especially the regional geodynamic environment and tectonic attribute of the Cenozoic basin’s formation.So there are still a series of problems should be further resolved.The characteristics of distribution,lithologic characteristic,sedimentary facies, environment evolution of current Tertiary and the characteristics of pre-Tertiary distribution and its contact with Tertiary have been identified through the three geological sections measured and other field sections investigation.It can be considered that during the Sikouzi period,the basin is composed by a number of interconnected or disconnected small fault depressions,the lake basin gradually increases at the Qinqshuiying period,and reaches to its peak at the Hongliugou period when the region has been basically connected to each other or become a larger group of lack basins,then the basin area become reduction at Ganhegou period.The 15 polarity and 14 anti-polarity records of Sikouzi have been gained by theMagnetostratigraphy method,which can be well compared with the standard polarity sequence.Multidisciplinary analysis indicate that the time-limit of Sikouzi group which is the first set of Ningnan Cenozoic sedimentary strata is from 47.9Ma to 29.4Ma B.P.namely in the Eocene and Early Oligocene.Moreover,the analysis and comparison is Made with the predecessors’ study in this area.It is considered that the deposition of Tertiary is in the tensional fault subsidence the same to the other fault subsidence of Ordos block in this period which is controlled by normal faults.After researching and analysis the geological structure,such as fracture,fold, unconformity contacts and inversion structures,is involved or formed by the Tertiary.It is considered that the Ningnan basin and peripheral Cenozoic faulted basins of Ordos block formation and development in the similar dynamic environment and the occurrence with a synchronous consistency,through the uniform contrast of the basins linked with regional,and research and analysis the unity and differences of tectonic evolution and activity of each other.The uplift and expansion of the Qinghai-Tibet Plateau has been strongly affected this area in Late Miocene.The development and evolution of Ningnan basin is obvious differentiation with the other peripheral faulted basins.The basin gradually disappearing by the reversal reformation.The intensity of reversal is weaker in the north than south,and the time is earlier at the south than north.更多还原