Magnetic evaluation of sediment provenance in the northern East China Sea using fuzzy c-means cluster analysis

To identify the provenance of fine-grained sediments in the northern East China Sea, various magnetic parameters indicating concentration (magnetic susceptibility, susceptibility of anhysteretic remanent magnetization (χARM), and saturation of isothermal remanent magnetization (SIRM)), mineral composition (S300 = − IRM− 300 mT / SIRM and HIRM (%) = 50 (SIRM − IRM300 mT) / SIRM), and grain size (frequency-dependent magnetic susceptibility (χFD), χARM / SIRM, and S20 = IRM20 mT / SIRM) were measured from surface sediments collected at 98 regularly spaced sites. As an unbiased analytic tool, fuzzy clustering analysis was performed on data from 97 sites except an outlier. Each dataset for each site comprised magnetic parameters representing ultrafine superparamagnetic (χFD), fine single-domain or pseudo-single-domain (χARM / SIRM), and coarse multidomain (S20) fractions, and the relative dominance of low- and high-coercivity minerals (S300 and HIRM (%), respectively). The statistical analysis yielded four clusters, indicating that the sediments in the study area can be differentiated magnetically. Of the magnetic properties of the cluster centers, the most distinctive feature of cluster 1 is a predominance of coarse-grained magnetic minerals (highest S20 value), while the contribution of high-coercivity minerals is highest in cluster 2 (highest HIRM (%) value). Ultrafine- and fine-grained fractions are prominent in cluster 3 (highest χFD and χARM / SIRM values), while cluster 4 has the highest ratio of low- to high-coercivity minerals (highest S300 value). Related to sediment provenance, the sediments of cluster 1 are interpreted to have been derived from the Yangtze River in China. The old Yellow River deposits are the primary source of sediments in cluster 2. Sediments in cluster 3 were probably transported from Taiwan or the Northwest Pacific by the Taiwan Warm Current or the Kuroshio Current, respectively, while Korean river deposits are the most probable sources of sediments in cluster 4.