浅谈长江和黄河河口沉积物磁性特征及其对物源判别的指示

Magnetic properties of sediments from the Changjiang and Huanghe River Estuaries and implication to provenance discrimination

对采自长江和黄河河口的7个沉积物样品(28个子样)进行了磁性测量并进行对比研究,结果表明:长江口沉积物的亚铁磁性物质含量高于黄河口,磁性强于黄河口;两河口沉积物的磁性特征均受亚铁磁性矿物的控制,以假单畴PSD-多畴MD晶粒为主,并存在一定量的超顺磁颗粒SP,不同的是长江口存在着更多的单畴颗粒SD;两河口的细粒级沉积物(<0.063 mm)磁性均强于粗粒级沉积物(> 0.063 mm),但黄河口细粒沉积物显示了更突出的磁性特征,表明黄河口沉积物的磁性物质更多地富集于细粒组分中;沉积物磁性特征与其所含的轻矿物类型和含量关系不大,相反,重矿物才是影响沉积物磁性特征的主要物质。沉积物的母岩、粒度、水动力条件和流域风化条件等因素影响着沉积物磁性特征。基于长江与黄河沉积物磁性参数的显著差异,建立了χ-χARM和SIRM-SOFT物源判别图,初步探索了环境磁学指标在物源判别中的应用,对中国东部海域沉积物的物源研究具有一定意义。

The magnetic properties of 7 sediment samples(with 28 subsamples) collected from the Changjiang and Huanghe River Estuaries were measured and compared. The results show that in the Changjiang River Estuary the magnetic intensity of sediments are stronger and the contents of ferrimagnetic substances are higher than that in the Huanghe River Estuary. The magnetic characteristics of sediments in the two estuaries are dominated by ferrimagnetic minerals. Pseudo-single domain(PSD) and multi domain(MD) particles are predominant in ferromagnetic crystal grain. Meanwhile, there are some superparamagnetic particles(SP). The difference is that there are more single domain particles(SD) in the Changjiang River Estuary.The magnetic intensities of fine-grained sediments(< 0.063 mm) are stronger than those of coarse-grained sediments(>0.063 mm) in both estuaries, but the fine-grained sediments in the Huanghe River Estuary show more prominent magnetic properties, which indicates that the magnetic properties in the Huanghe River Estuary are supremely rely on the contribution of fine-grained sediments. The magnetic properties of sediments are generally not related to the light minerals. On the contrary,heavy minerals are the main substances affecting the magnetic properties of sediments. The magnetic properties of sediments are influenced by the factors such as parent rock, grain size, hydrodynamic conditions and weathering conditions of the basin.Based on the conspicuous differences of magnetic parameters between the sediments of the Changjiang River and the Huanghe River, the χ-χARM and SIRM-SOFT provenance discrimination diagrams are established and the application of environmental magnetic indicators in the provenance discrimination is preliminary studied, which will benifit the study of sediments provenance in the East China Sea.