末次冰期鄱阳湖西南缘地区的风尘堆积

鄱阳湖湖滨沙山是末次冰期特定气候条件下季风活动所产生的风成沙丘沉积体。在调查鄱阳湖沙山的过程中,发现位于鄱阳湖南部沙山下风方向的丰城-樟树-新余一带岗丘顶部几米厚的第四纪堆积地层,虽然颜色明显偏红,但地层性状及沉积学特征却与北方风成黄土及宁镇下蜀黄土有着很大的相似性。通过对具代表性的新余打鼓岭剖面进行分析,确认其成因系风力搬运而成的粉尘堆积。结合冬季风路径上沉积物粒度的空间变化特征,初步提出鄱阳湖沙山与新余一带风尘红土堆积是在末次冰期特定气候条件下,冬季风作用所形成的风沙-风尘堆积系统。鄱阳湖风成沙丘及其西南缘风尘沉积的发育是晚更新世末期江南鄱阳湖区气候环境恶化的佐证,也是对我国西北地区沙漠-黄土堆积过程的区域响应。

AEOLIAN-DUST DEPOSIT TO THE SOUTHWEST OF THE POYANG LAKE DURING THE LAST GLACIAL AGE

The sandy hills(namely Shashan) on the shore of Poyang Lake were aeolian-dunes formed by winter-monsoon in the last glacial age.In the course of investigating the environment of the sandy hills,the authors found that deposit strata situated to the leeward of the Shashan,were very similar to the northern aeolian-dust loess and the Xiashu loess near the Yangtze River.According to typical study on Daguling section in Xinyu City,they were the aeolian-dust deposit developed in the last glacial age.On the basis of analyses on the features of distribution,material component,sedimentary structure,and spatial change of grain-size and formation age of the Quaternary deposit from Poyang lakeside to Xinyu City,the authors suggested that they should have been the aeolian-dunes and their derivative aeolian-dust system formed by paleo-monsoon in the special climatic condition since the last glacial stage.During the last glacial stage,the continental climate in the south Yangtze River area greatly strengthened and the strong winter-paleo monsoon deflated the Poyang Lake area.It revealed the abundant sands of the lakes and rivers and developed "desertification environment".The coarse sand on the beaches of the lakes and rivers was eroded and gathered near the Poyang lakeside,and formed aeolian-dunes(namely Shashan).While the fine sand and dust material were carried and transported to leeward,and deposited around the Xinyu as the derivative aeolian-dust of the Shashan.The aeolian-dunes near the Poyang lakeside and their derivative aeolian-dust near the Xinyu constitute a special geographic environment system formed by the interaction of atmosphere,hydrosphere and geosphere since last glacial stage in the Poyang Lake area.Their development provided evidence for environment degeneration of Boyang Lake area since late Pleistocene,and is also regional response to the desert-loess deposition in northwest China.