Palaeoenvironmental Evolution of Subaqueous Yangtze Delta Inferred From Sedimentary Records

Characteristics and Environmental Indications of Grain Size and Magnetic Susceptibility of the Late Quaternary Sediments from the Xiyang Tidal Channel, Western South Yellow Sea

“…The magnetic susceptibilities are relatively high and significantly fluctuating, which is related to the fact that the magnetic minerals are mainly enriched in the coarse-grained components and is further indicative of the tidal estuarine marginal bank and river bed environments under the high sea level and the influence of relatively strong hydrodynamics during the warm period of MIS 7. The results of previous studies show that the Changjiang River-derived sediments are relatively coarse in grain size and relatively high in magnetic susceptibility, and the magnetic minerals are mainly enriched in the coarse-grained sediments [12,13,20]. The characteristics of the grain size and magnetic susceptibility of core 07SR01 sediments in this stage are similar to the above-mentioned features.…”

“…Variations in the grain size and magnetic susceptibility of sediments in the river-sea interaction area could indicate environmental changes [4][5][6][7][8][9][12][13][14][15][16]50]. In addition, the above analyses show that the grain size and magnetic susceptibility of core 07SR01 sediments responded well to the changes in sedimentary environments.…”

“…Therefore, magnetic susceptibility rapidly became an important proxy for environmental changes, and it has received wide attention and been applied in the environmental studies of loess, lakes, and deep seas [11], while it has been applied later in the studies of estuaries, coasts, and deltas, where the sea-land interactions and sedimentary environments are complex and varied, but good research results have also been achieved. For example, Jia et al and Zhang et al [12,13] found that the magnetic susceptibility of estuarine core sediments can indicate the strength of hydrodynamics to a certain extent, indirectly reflecting the evolution of sedimentary environments, and a high value of magnetic susceptibility indicates stronger hydrodynamics, while a low value indicates weaker hydrodynamics. Ge [14] studied the magnetic susceptibility of core QC 2 sediments in the South Yellow Sea, showing that the variation characteristics of magnetic susceptibility basically reflect the variation pattern of climatic environments, i.e., the magnetic susceptibility increased relatively in the warm and humid period and decreased relatively in the cold and dry period.…”

Response of Shallow Gas‐Charged Holocene Deposits in the Yangtze Delta to Meter‐Scale Erosion Induced by Diminished Sediment Supply: Increasing Greenhouse Gas Emissions

“…From the perspective of stratigraphy and lithology, shallow gas originates from muddy facies corresponding to Holocene TST and HST sediments. Sediment cores from different regions of the subaqueous delta indicate that the total organic carbon content in sediments throughout the Holocene from the TST to the HST is generally 0.5% or higher (Wang, 2011;Wang et al, 2012;Zhan et al, 2011;Zhang, Jin, et al, 2015;Zhang et al, 2011), which is above the threshold value for gas generation (Rice & Claypool, 1981). Although the masking effect hinders the identification of deeper gas horizons, most Holocene sediments below the gas front are likely gas-charged.…”