后沙峪凹陷第四纪高精度地层格架及地质意义

High Precision Stratigraphic Framework of Quaternary and Geological Significance in Houshayu Sag

通过对后沙峪凹陷ZK19钻孔自然伽马测井曲线进行旋回地层分析,以古地磁测年数据为年龄锚点,建立了后沙峪凹陷第四纪0.1 Ma年精度的年代标尺,为后续研究后沙峪第四纪的构造演化、气候变化提供了精细的年龄标定。通过对钻孔ZK19开展沉积相分析,将地时与沉积相分析相结合,讨论本区第四纪以来的沉积演化,以及沉积环境对第四纪新构造运动的响应。分析表明,钻孔中识别出的两次浅湖沉积,沉积时间分别为2240~2152 ka,1784~1475 ka,分别对应了早更新世早期的西山强烈上升时期和早更新世中期的青藏运动B幕,北京地区构造以北东向断裂活动为主导。根据后沙峪凹陷浅湖相的消亡时间,确定后沙峪凹陷的形成时间大概2080 ka。晚更新世以来,北东向断裂表现为整体运动,两盘差异不大,后沙峪地区主要为曲流河的沉积环境。

Through cyclic stratigraphy analysis of natural gamma logging curve of borehole ZK19 in Houshayu depression,and taking paleomagnetic dating data as age anchor,the age scale of Quaternary in Houshayu depression was established,and it provided a fine age calibration for the follow-up study of the Quaternary tectonic evolution and climate change of Houshayu depression.By the combination of geotime and sedimentary facies study,the sedimentary facies of borehole ZK19 was analyzed to discuss the sedimentary evolution since Quaternary and the response of sedimentary environment to Quaternary Neotectonic Movement.Two stages of shallow lake deposits in the borehole are identified in 2240~2152 ka and 1784~1475 ka respectively,corresponding to the strong-uplifting period of Xishan in early Pleistocene and the Qinghai-Tibet movement B in Middle Early Pleistocene,then the geologic structures in Beijing area is dominated by the north-east trending faults.According to the extinction time of shallow lacustrine facies in Houshayu depression,the formation time of Houshayu depression is defined in nearly 2080 ka.Since the late Pleistocene,the NE trending fault has been moving as a whole,with little difference between the two sides,and the Houshayu area is mainly in the sedimentary environment of meandering river facies.