长江口现代潮滩表层沉积物磁性特征和自生铁硫化物的分布

Magnetic properties of surficial sediments and distribution of authengenic iron sulfide in modern tidal flat at Yangtze estuary

以长江口崇明岛北支潮滩的3个潮滩为对象,在粒度测量和磁性分析的基础上,揭示了现代潮滩表层沉积物的磁性变化,探讨了磁性矿物、尤其是自生亚铁磁性矿物—硫复铁矿(Fe3S4)在潮滩沉积微相的分布规律及机制。研究结果表明:长江口潮滩表层沉积物的磁性特征由亚铁磁性矿物及超顺磁颗粒(SP)主导。淤积型中高潮滩磁铁矿以单畴(SD)和SP为主,侵蚀型潮滩的中低潮滩则更多假单畴/多畴(PSD/MD)晶粒,反映了水动力的分选及以细颗粒矿物溶解为主的早期成岩作用。此外,最东侧的北四滧港剖面潮上带—高潮滩芦苇带普遍存在自生亚铁磁性硫复铁矿,北堡港和新卫剖面的高潮滩也局部存在硫复铁矿,反映了本区高潮滩—潮上带丰富的有机质及细颗粒沉积物、加上有限的海水淹没时间,是早期成岩作用过程中生成硫复铁矿的主要机制。

The present paper measured grain size and magnetic parameters to examine magnetic prop- erties and the distributions of magnetic minerals, especially the authengenic greigite （Fe3S4） along the tidal flat sections from the northern coast of Chongming island, Yangtze estuary. The results revealed that ferromagnetic minerals and superparamagnetic （SP） minerals are predominant in the surficial sediments. Single-domain （SD） and superparamagnetic （SP） grains prevail in the sediments of high to middle tidal flat from progradational coast. By contrast, the major magnetic feature of middle and lower tidal flat sedi-ments from the regradational coast is dominated by pseudo-single domain/multi-domain （PSD/MD） grains, reflecting the hydrodynamic sorting and dissolution of fine-grained magnetite during the early dia- genesis. Moreover, authengenic greigite occurs generally in the reed zone of supra and high tidal flat of Beisiyaogang section which is located easternmost, while it also exists locally in the high tidal flat of Bei- pugang and Xinwei sections, reflecting that organic matter and fine-grained sedments can generate greigite with the limited inundation time of sea water in the study area.