福建九龙江河口潮滩沉积物磁性矿物时空分布特征及其沉积学意义OACHSSCD

Because of the complex hydrodynamic conditions,it is difficult to identify the elaborate characteristics of sedimentary differentiation in estuary tidal flat.The construction of index system of tidal flat sediment differentiation is the basic link to identify the sediment microfacies and to reveal the evolutionary trend of tidal flat.In this study,three sediment cores were obtained from the tidal in the Jiulong River Mouth in three sedimentary environments:upper tidal flat,middle tidal flat and lower tidal flat,and their 137Cs dating analysis,grain size analysis,and room-temperature magnetic measurements were conducted.This study investigates the distribution characteristics of magnetic minerals in tidal flat sediments and their indicative significance for sedimentary dynamics.The results showed that:(1)The tidal flat in the east of Humaozhou Island presents high deposition rate.The sedimentation rate of upper-middle tidal flat is higher than that of lower tidal flat,which is mainly influenced by tidal wave dynamics and vegetation promoting siltation.(2)Fine-grained magnetic minerals SP and SD grains are enriched in upper-middle tidal flat,while coarse-grained magnetic minerals MD and PSD grains are enriched in lower tidal flat,revealing that magnetic minerals of the tidal flat are controlled by hydrodynamic separation.The high values of SIRM/x and S-20mt appear in the magnetic characteristics of the sediments in the upper-middle tidal flat,reflecting the existence of early diagenesis.(3)There is a highly significant difference in xfd％,xARM/x and xARM/SIRM in sediments of the tidal flat.We thus proposed that the combination of these magnetic parameters can be used as potential indicators to distinguish sedimentary facies between upper-middle tidal flats and lower tidal flat in the Jiulong River mouth.This study provides a sedimentological index reference for the study of tidal flat evolution and the identification of tidal flat sedimentary microfacies on a century-to-decade scale.