Influence of provenance and hydrodynamic sorting on the magnetic properties and geochemistry of sediments of the Oujiang River, China

We present the results of environmental magnetic, granulometric and geochemical analyses of sediments of the Oujiang River, China. The aim of the study was to assess the influence of hydrological sorting and sediment source on sediment composition from upstream down to the river mouth. The results reveal that the sedimentary magnetic properties are dominated by ferrimagnetic minerals. In the fluvial reach, the proportion of imperfect antiferromagnetic minerals is relatively high due to strong soil chemical weathering in a subtropical climate. From upstream down to the river mouth, the proportion of ferrimagnetic minerals increases consistently, and the magnetite becomes finer-grained as a result of hydrological sorting. In the tidal reach, the sediments consist of a mixture of fluvial and marine-sourced sediments derived from the Yangtze River as a result of the strong tidal influence. A combination of the demagnetization parameter S− 100 mT and element ratios (Fe/K and Al/Mg) enables the discrimination of the sediments of the fluvial reach from those of the tidal reach. Due to the rock types and subtropical weathering conditions in the catchment, the sediments of the Oujiang River are significantly different to those of the Yangtze River. Our results potentially contribute to the study of the provenance of the muddy sedimentary deposits in the inner East China Sea. They demonstrate that sediment sorting has a significant effect on bulk magnetic properties and geochemical compositions during transport from source to sink. In addition, magnetic and geochemical characterization of sized fractions of sediment can provide more reliable information regarding sediment source tracing.