Magnetic properties of particle-sized fractions of sediments in the Changjiang Estuary and neighboring shelf, and its environmental implications

GE Can; ZHANG Weiguo

doi:10.3969/j.issn.1000-5641.2021.02.004

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GE Can, ZHANG Weiguo. Magnetic properties of particle-sized fractions of sediments in the Changjiang Estuary and neighboring shelf, and its environmental implications[J]. Journal of East China Normal University (Natural Sciences), 2021, (2): 30-41. doi: 10.3969/j.issn.1000-5641.2021.02.004

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GE Can, ZHANG Weiguo. Magnetic properties of particle-sized fractions of sediments in the Changjiang Estuary and neighboring shelf, and its environmental implications[J]. Journal of East China Normal University (Natural Sciences), 2021, (2): 30-41. doi: 10.3969/j.issn.1000-5641.2021.02.004

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Magnetic properties of particle-sized fractions of sediments in the Changjiang Estuary and neighboring shelf, and its environmental implications

doi: 10.3969/j.issn.1000-5641.2021.02.004

GE Can^{1, 2, 3
,},
ZHANG Weiguo^{2
,
,}

1.
Zhejiang Institute of Hydraulics and Estuary, Hangzhou　310020, China
2.
State Key Laboratory of Estuarine and Coastal Research, East China Normal University, Shanghai　200241, China
3.
Zhejiang Provincial Key Laboratory of Estuary and Coast, Hangzhou　310020, China

Received Date: 2020-04-17
Publish Date: 2021-03-30

Abstract

Abstract

Twenty-two surface sediments collected from the Changjiang Estuary and neighboring shelf were subjected to particle-size measurements, with the intent of understanding the implications for provenance, transport, and depositional dynamics. The results showed that Changjiang River-derived sediments, relict sands, and Yellow River-derived sediments were the primary sources controlling the magnetic properties of sediments in the study area. The three areas, however, exhibited different spatial distributions. Spatial variations of magnetic parameters, including magnetic susceptibility (χ), saturation isothermal remanent magnetization (SIRM), hard isothermal remanent magnetization (HIRM), and anhysteretic susceptibility (χ_ARM), suggest that sediments from the Changjiang River are transported towards the south and southeast when they move out of the river mouth. According to bi-plots of SIRM versus χ and S-ratio (S_–100) versus SIRM, the > 63 μm fraction is roughly bounded by the 30 m isobaths that separates the Changjiang River sediment from the relict sands on the shelf. The < 16 μm fraction is derived mainly from the modern fluvial sources of the Changjiang and Yellow Rivers; in particular, the Changjiang River-derived sediment dominates the inner estuary and the Yellow River-derived sediment dominates the northern coast of the shelf. The other areas of the shelf are characterized by mixed sources of the < 16 μm fraction, with a majority being Changjiang River-derived sediment. Spatial variations of particle size compositions and magnetic properties reflect the role of hydrodynamic sorting on particle size as well as mineral density; this results in differences in magnetic properties among the sedimentary units as well as the contribution of different sized fractions to the bulk SIRM values. Particle size separation could reduce the effect of particle size on bulk magnetic properties and lead to more precise provenance discrimination. Our results have great potential in the study of geomorphological changes and quantitative source identification in delta environments.
- magnetic properties,
- particle size separation,
- provenance,
- hydrodynamic sorting,
- Changjiang Estuary,
- East China Sea shelf

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References(39)

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