西北干旱环境始于何时

WHAT TIME WAS BEGUN ARID ENVIRONMENT IN THE NORTH-WEST OF CHINA

湖泊、黄土、沙漠及动植物群等第四纪发展历史表明,西北现代干旱环境并非始自第三纪末第四纪初,而是从距今1.4～1.2百万年的第四纪中期开始,其原因在于青藏高原及西北诸大山系上升的年青性与加速性。

Quaternary history of lakes, loess, deserts, Vegetation and paleo-fauna ete.makes known that arid environment in the North-West of china was begun at middle stage of Quaternary period(1.4-1.2M.Y.B.P),was not begun from last stage o(?) Tertiary periodto early stage of Quaternary period.The cause lie in young and guicking quality of the upliftof the Qinghai-Xizang Plateau and high mauntains in the North-West o(?) China.