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兰州地区位于黄土高原和青藏高原的过渡带,其第三纪地层对研究风尘沉积发育和青藏高原隆升都有着特殊的意义.本研究以0.5 m间距对兰州盆地皋兰山剖面240 m的晚第三纪地层进行古地磁样品采集,古地磁样品共计422个;以50℃为间隔从室温至500℃用热退磁仪和超导磁力仪完成了皋兰山剖面样品的系统热退磁和剩磁测量.结果表明皋兰山剖面上部地层的实测极性柱出现2个负极性大段中间夹着4个正极性小段,其特点与Gilbert时的典型特征完全一致,并且两端未完全出露的正极性分别与Chron2A.3n和Chron3An.1n相对应,最终确定皋兰山剖面的年代为6～3.5 Ma.由此推断,皋兰山剖面顶部的五泉砾岩形成大约开始于3.5 Ma,五泉砾岩底界年代的确定,为青藏高原的A幕运动提供了地质证据.皋兰山剖面深度602 m处出现由河湖相砂岩向以风成红粘土为主常夹有薄层砂岩的地层转变,通过岩性地层及年代的推断,兰州地区的风尘序列堆积发育的年代至少为7 Ma,与黄土高原风尘序列堆积底界8～7 Ma基本一致,说明了兰州地区与黄土高原在风尘序列堆积过程中具有统一性.
The Lanzhou region is located in the transitional zone between the Loess Plateau and the Qinghai-Tibet Plateau, and its Tertiary stratigraphy is of special significance for studying the development of dust deposits and the Qinghai-Tibet Plateau uplift. In this study, Paleomagnetism samples were collected in the Tertiary stratigraphy, a total of 422 paleomagnetic samples were collected. Thermal demagnetization and remanence of the samples from Gaolan Mountain section were completed by thermal demagnetization and superconducting magnetometer at room temperature from 50 ℃ to 500 ℃. The results show that there are 4 positive polar segments in the middle of the positive polarity column in the upper strata of Gaolan Mountain section, which are characterized by exactly the same characteristics as those of Gilbert, and are not completely exposed at both ends The positive polarity corresponds to Chron2A.3n and Chron3An.1n respectively, and the Gaolan Mountain section is finally confirmed to be 6 ~ 3.5 Ma in age, which indicates that the formation of Wuquan conglomerate at the top of Gaolan mountain section starts at about 3.5 Ma and Wuquan gravel The determination of the age of the subterranean boundary provided geological evidence for the movement of A in the Qinghai-Xizang Plateau.The formation of the sandstone at the depth of 602 meters at Gaolan Mountain changed from fluvial-lacustrine sandstone to aeolian red clay Through the rock Stratigraphy and age, the age of dust accumulation sequence in Lanzhou is at least 7 Ma, which is basically the same as that of the 8-7 Ma at the bottom of the dust accumulation sequence in the Loess Plateau, indicating that Lanzhou and the Loess Plateau have a unified Sex.