乌兰布和沙漠形成时代的初步判定及意义

根据乌兰布和沙漠和沙漠北部出露的剖面记录，初步确认了全新统风成砂沉积层的划分，并据此作14C测年分析，认为全新世风成砂至少形成于2个时期：早全新世，14C年龄为距今7255a之前;晚全新世，14C年龄为距今2255或2630a以近，两期风成砂之间则是一个湖沼广泛发育的时期，乌兰布和沙漠形成时代的初步判定，至少可以认为在人类大规模开垦的汉代之前沙漠就已形成，且已经历了风成砂一湖沼的变化过程，说明沙漠的形成仍是以自然因素为主的过程，人类活动影响只是一个叠加于其上的因素．

A STUDY ON FORMING TIME OF ULAN BUH SANDY LAND AND ITS MEANNING

Based on the profile at the North part of Ulan Bub Sandy Land, layer of eolian sand is devided and its 14C date is determined. It is stated that the Holocene eolian sand formed in two stages at least: one epoch is in early Holocene, 14C date is before 7 255 a B. P., another is inlate Holocene, 14C date is after 2 255 or 2 630 a B. P.. Between two layer of wind drift sand, there is a lake and swamp evolution stage. So the forming time of Ulan Bub Sandy Land is deter mined at the stage before Han Dynasty, when human had not opened up the ground. The evolution process of the sandy land is based on natural factor mainly, and Ulan Bub Sandy Land is not a manmade desert.