AGE OF THE VERMICULATED RED SOIL IN JIUJIANG AREA,CENTRAL CHINA

There is a wide distribution of the vermiculated red soil in the middle and lower reaches of the Changjiang River.A preliminary study of the Changhongdadao profile in Jiujiang City was carried out in this paper.In the profile,the strata can be divided from the bottom upwards into fluvial sandy gravel,horizontally vermiculated ferruginous red soil,vertically vermiculated red soil,red clay and eolian Xiashu loess,3.3m,4.5m,5.9m,3.6m and 4.1m thick respectively.The boundary between the Brunhes normal zone and the Matsuyama reversed zone is know from magnetostratigraphic study to occur in the middle part of the vermiculated red soil bed at a depth of 12.9m and the Jaramillo normal subzone in the ferruginous vermiculated red soil bed at a depth of 15.1m to 16.1m.The average sedimentation rate is calculated by Cande and Kent's palaeomagnetic age model and by thermoluminescent dating and hence the age of bed boundaries.The results show that the ferruginous vermiculated red soil was deposited during 1.232-0.869MaBP,the vermiculated red soil during 0.869-0.392 MaBP and the red soil during 0.392-0.101MaBP.
The sedimentary sequence in the Changhongdadao profile indicates a periodic climate change of about 0.4Ma.It is consistent with the tectonoclimatic cycles as revealed by the tectonic layers in the Loess Plateau and the Qinghai-Tibetan Plateau and the change of the earth's orbital eccentricity.