青藏高原碰撞—隆升阶段班戈县恐弄拉地区古近纪盆地演化特征浅析

Basin Evaluation Features Discussion of Paleogene in Collision-uplift Stage in Kongnongla Area of Bange County,Tibet Plateau

新生代,青藏高原进入陆内造山及其后的整体隆升阶段,据此形成一系列山间断陷盆地,此时期盆地充填古新—始新统牛堡组沉积,即早中期为冲积扇—河流相沉积环境;中期为湖泊三角洲相沉积环境;中—晚期为淡水湖泊相沉积;晚期为陆内盐湖相沉积。通过对牛堡组沉积相的分析,可以提供剥蚀区与沉积区的空间分布情况,间接反映研究区的古地理面貌,故而进一步探讨古近纪盆地演化历程,即由初陷期半封闭型河湖盆,向深陷期开放型湖盆,至收缩期封闭型湖盆的演化过程。同时也从侧面反映构造演化的发展及沉积盆地响应过程与古气候的耦合关系。

In the Cenozoic era,Tibet entered intracontinental orogenic and later uplift stage,so a series of intermountain fault basin formed,the basin filled sediment in Niubao formation of Paleocene-Eocene,the early-middle stage is alluvial fan-fluvial facies sedimentary environment,the middle stage is lake delta facies sedimentary environment,the middle-late stage is fresh lake facies sediment,the later stage is interior lake facies sediment. By analyses the sedimentary facies of Niubao formation,the spatial distribution of denuded zone and depositional zone are known,it reflects the paleogrographic landforms of the target area indirectly,then the basin evaluation process in Paleogene is discussed： semi-closed lake basin in the early sag stage,open lake basin in deep sag stage and close lake basin in contraction stage. Meanwhile,it reflects the coupling relation of structural evaluation,depositonal basin responding process and ancient climate.