Spatial variation of the magnetic properties from the yangtze river subaqueous delta deposits and their implications for erosion/deposition study

Delta deposits show great spatial heterogeneity in erosion and depositional patterns. Magnetic properties of sediments are sensitive to the sediment source, hydrodynamics, and early diagenesis and, therefore, can indicate spatial heterogeneity in an efficient way. In this paper, four cores (ca. 2 m in length) from the subaqueous Yangtze River Delta were subjected to environmental magnetic, organic carbon, and sulfur analyses. In combination with particle size analysis and dating results, this paper discusses the spatial variations of magnetic properties and their implications for indicating erosion/deposition patterns. Our results show that hydrodynamic sorting plays an important role in the magnetic property variations. In general, ferromagnetic minerals are enriched in fine-grained sediments in young deposits (<350 a), resulting in higher magnetic susceptibility (χ). The Yangtze River subaqueous delta deposits exhibit a weaker sulfate reduction, as revealed by carbon, sulfur, and sulfur isotope characteristics. Such a feature is similar to that reported from Amazon delta deposits. Sediment age and sedimentation rate affect the degree of diagenetic alteration, and therefore, the spatial and temporal variations of magnetic properties. Cores distant from the modern depo-center show a greater diagenetic alteration of magnetic properties. Magnitude of χ, diagenetic zonation of χ, and the depth of the ferruginous to sulfidic boundary can reflect the spatial pattern of erosion and deposition in deltaic deposits.