中全新世以来长江口北支环境的演变

从古环境演变的角度,对崇明岛北侧的永隆沙钻孔进行了系统的采样和粒度分析、微体古生物分析、环境磁学分析以及14C测年等。大致恢复长江口北支古地理环境演变的过程,中全新世以来,长江口北支由浅海沉积环境,逐渐演变为三角洲平原环境。但通过环境磁学和微体古生物分析,揭示了在2080~2000 aB.P.,700~625 aB.P.这两段历史时期,长江口北支表现为河口砂坝亚环境和河口河槽亚环境。这两次环境变异事件记录了长江主泓南北迁移的事实。

Evironmental evolvement of the north branch of the Changjiang estuary since middle holocene

The research on environmental evolvement of the north branch of the Changjiang estuary has mainly been focused on the modern aggradation and analysis of the sediment process of the north branch of the Changjiang estuary through the conditions of hydrodynamic, while research work on the evolvement of paloenvironment has been ignored. Many systematic samplings in the profile of the CY core which lies in the north of the Chongming island had been chosen. Based on a comprehensive analyses of the content variation of grain size, the magnetic analysis, the foraminifera analysis and other analyses, it can be found that the environmental evolvement of the north branch of the Changjiang estuary has been found since middle-holocene. This region was located from shallow sea facies tO delta complain facies. But from the ananlyses of magnet and foraminif- era, during 2 080-2 000 aB. P. and 700-625 aB. P. periods, the facies are barrier sand and scoured riverbed. These two events recorded the changes of the Changjiang estuary.