AGE OF THE VERMICULATED RED SOIL IN JIUJIANG AREA,CENTRAL CHINA
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摘要: 长江中下游地区广泛发育网纹红土。本文对九江长虹大道剖面进行了初步研究。该剖面地层自下而上可分为河流相冲积砂砾石、以发育水平状网纹为特征的铁质网纹红土、以垂向网纹为特征的网纹红土、红色粘土和风成下蜀黄土,分别厚3.3、4.5、5.9、3.6和4.1m。磁性地层研究结果,布容正向极性带/松山反向极性带的界限出现于网纹红土层中部,距顶深部12.9m处;贾拉米洛正向极性亚带出现在铁质网纹红土层中,距顶深度15.1-16.1m处。根据CandeandKent古地磁极性年表的模式年龄和热释光年龄,计算出沉积速率,进而计算出各层的界限年龄。结果表明,铁质网纹红土沉积于1232-869kaBP;网纹红土大约沉积于869-392kaBP;红色粘土沉积于392-101kaBP。九江长虹大道剖面代表了该地区从河流沉积、铁质网纹红土、网纹红土、红色粘土到风成黄土沉积的演变过程,并显示出准0.4 Ma的周期变化。这与黄土高原、青藏高原构造层和地球公转轨道偏心率变化所反映的准0.4 Ma构造气候旋回基本一致。Abstract: 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.
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Key words:
- vermiculated red soil /
- geologic age /
- periodic climate change /
- Jiujiang
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