宁夏卫宁盆地晚新生代沉积序列与环境演变研究

The north eastward growth of the Tibetan Plateau is involved in important scientific problems about lithospheric dynamics of the plateau and has important theoretical and practical significances. Zhongwei-Zhongning basin is located in the arc tectonic mountains in the northeastern margin of the Tibetan Plateau, which is the newest deformation front area in the northeast edge of the plateau since the late Cenozoic. There had strong tectonic deformations, basin sedimentary sequences and sedimentary environment evolutions recorded rich orogenic belt uplift informations. So, it is an ideal area for the plateau rising process research. This project intends to start from the Neogene sedimentary strata and morphostructure, and to choose the typical Neogenic stratigraphic sections for field measurements and system sampling tests. It will invert the stratigraphic deposition phases and the evolution process of sedimentary environment in the western margin of the Niushou mountain by comprehensive analysis of the sedimentology features, magnetic stratigraphies, biostratigraphies, deposition phases and tectonic sequences in Zhongwei-Zhongning basin. The Project will investigate the tectonic properties and evlution history of Zhongwei-Zhongning basin and abstract the informations of tectonic activities around the orogenic belt. In the end, this reasearch will reveal the evolution of the arc tectonic mountains formation in the north eastward of the Tibetan Plateau, and provide scientific basis for the studies of the plateau growth and lithospheric dynamics through the comprehensive analysis of the arc tectonic mountains.

青藏高原北东向扩展和隆升是涉及高原隆升动力学机制的重要科学问题，具有重要理论和现实意义。卫宁盆地位于青藏高原东北边缘的弧形构造山地，是晚新生代以来高原东北边缘最新变形前缘区，构造变形强烈，盆地沉积序列和沉积环境演变过程记录了丰富的造山带隆升信息，是开展青藏高原北东向扩展和隆升过程研究的理想地区。本项目拟从新近纪沉积地层和构造地貌入手，在牛首山西缘选择典型新近纪地层剖面实测并系统采样测试，通过对卫宁盆地沉积学特征、磁性地层、生物地层、沉积相和构造层序的综合分析，反演牛首山西缘地层沉积相和沉积环境演变过程；通过对盆地内阶地等层状地貌面时代和变形规律的研究，探讨卫宁盆地的构造属性和演化历史，提取周围造山带的构造活动信息。最终通过对四列弧形山地的综合分析，揭示青藏高原东北缘弧形山地形成演化规律，为青藏高原隆升过程和动力机制研究提供科学依据。

宁夏中南部断陷盆地区是青藏高原北东向扩展影响的最新变形区，盆地内厚层古近系-新近系沉积序列忠实记录了四列弧形构造带的构造活动和区域沉积环境演变过程，也是开展青藏高原隆升和北东向扩展过程及其动力学机制等科学问题研究的良好载体。然而，由于缺乏对各组地层年代格架的准确厘定及区域古地理格局的重建，严重制约了认识的深入。. 项目重点对牛首山断裂带新田-白马剖面红柳沟-干河沟组进行了实测和系统的磁性地层学研究,明确了红柳沟组岩石地层单元界面的标志岩性，建立了沉积序列和年代标尺。研究表明红柳沟组厚1020米，形成于18.57-8.97Ma；干河沟组厚567.5米，形成于8.97-3.0Ma。依据红柳沟组界面标志岩性，重新厘定了香山-天景山断裂带贺家口子剖面清水营组、红柳沟组地层序列和年代标尺，确定清水营组形成于22.92 - 16.62Ma；红柳沟组形成于16.62 - 7.83Ma。根据两个剖面中沉积速率的变化，确定牛首山断裂带在18.8 Ma、15.2 Ma、8.7 Ma和5.2 Ma，香山-天景山断裂带在20.1 Ma、17.3 Ma、15.2 Ma和7.7 Ma发生活动强烈。利用重矿物鉴定和碎屑锆石U-Pb年龄示踪方法分别对牛首山断裂带和香山-天景山断裂带古近系-新近系各组地层、卫宁盆地及周边各级水系主要河流阶地堆积的物源进行了分析，结果表明自晚始新世寺口子组至上新世干河沟组堆积时期，盆地沉积明显受断裂带活动控制，且盆地沉降中心自固原地区向北逐渐迁移。第四纪期间的地貌格局已基本定格，大型水系沿山间分布，构造运动未明显改造地理格局。. 宁夏中南部断陷盆地区的古近系-新近系沉积地层、断裂带的活动时序还是区域古地理格局和沉积环境的演变过程，均表明自晚始新世寺口子组开始沉积以来，随时间的推移，表现出由南向北不断发展的规律变化，其演化过程受青藏高原阶段性隆升和向北东扩展作用的控制。