| Nantong of Jiangsu Province is located at the Yangtze River paleo-incised-valley. The Holocene deposits there record environmental evolution history and paleoclimate information, and therefore received wide attention. In this study, core NT was obtained from Nantong, Jiangsu, which covers the period of Holocene according to AMS14C dating. Rock magnetism was carried out on samples from core NT. In combination with analysis of particle size, geochemistry, heavy minerals, X-ray diffraction (XRD), diffuse reflectance spectroscopy (DRS), scanning electron microscopy (SEM) and AMS14C dating, this paper analyses magnetic properties of core NT, its influencing factors and discusses its environmental implications.1. Core NT shows marked downcore variations in particle size. According to stratigraphic correlation, core NT can be divided into the following facies in ascending order:tidal channels facies (U1), tidal flat-estuary facies (U2), tidal sand ridge facies (U3), prodelta facies (U4), delta front facies (U5) and tidal flat facies (U6), respectively. It shows a relative complete cycle of transgression and regression.2. Magnetite dominates magnetic properties of core sediments, antiferromagnetic minerals contribute significantly in tidal flat facies. In certain layers, higher SIRM/χ, S-300 and S-100 values indicate the presence of greigite, which is confirmed by SEM analysis.3. The geochemical composition and heavy minerals analysis suggest significant variations in sediment sources. However, it has minor impact on magnetic properties.4. Particle size plays an important role in the variation of magnetic properties. Mean size and fraction coarser than 64μm are positively correlated with magnetic susceptibility (x) in most layers, which suggests that magnetic minerals are mainly enriched in the coarser sand fractions.5. Post-depositional secondary changes also have an impact on magnetic properties in sediments. The occurrence of greigite prove remarkable influence of early diagenesis. Enrichment of antiferromagnetic minerals in tidal flat sediments is caused by pedogenesis. The difference of magnetic properties in different tidal flat facies indicates different sedimentary evolution process during the early and late Holocene, i.e., retrogradation in early Holocene (U2) and progradation in late Holocene (U6), respectively.6. The response of magnetic minerals to post-depositional secondary changes can be used to qualitatively reflect pedogenesis time and climate conditions in the tidal flat of Yangtze delta, are the depositional rate and sedimentary units transition. It is an effective method for stratigraphic division. |
PDF Full Text Request