兰州地区晚第三纪磁性地层与古环境意义

he absolute depth of Gaolan Hill section in Lanzhou is 240m totally， 422 paleomagnetic samples were collected with 0.5m intervals in the section. Thermal demagnetizer and cryogenic magnetometer were used to systematically measure the magnetic remanence from room temperature up to 500℃ with 50℃ step in order to dertimime magnetostratigraphy of the Gaolan mountain section. In the result, the trait of Magnetic polarity of Gaolan mountain section is that 2 long negative Polarity Subchron are in both sides and 4 short positive Polarity Subchron are inside. It is identical with Gilbert Chron. The magnetostratigraphy age span of the Gaolan mountain section is from 6MaB.P. to 3.5MaB.P. .On the basis of the analysis of the Magnetic polarity boundary ages and sediment rate correspondingly, the bottom age of Wuquan conglomerate of Lanchow area is about 3.5MaB.P.,which provide geological evident for the Qinghai-Tibet Plateau uplift events in the 3.6MaB.P.; Eolian sequence accumulation is occurred from 7 MaB.P. at least. Ancient monsoon climate and western aridification had been formed. The age is identical nearly with the bottom age of eolian sequence accumulation in Loess Plateau.