1080 / 2019-07-13 14:35:36

Magnetic evidence for Yellow River sediment in the late Holocene deposit of the Yangtze River Delta, China

6、海洋地球科学 > 专题5：从流域到深海：沉积物的产生，搬运和埋藏

Sediment source identification is critical to understand delta evolution process and for managing delta environments, particularly for those deltas facing significant fluvial sediment discharge. The Yangtze River Delta (YRD) is a tidal-dominated delta, which can receive marine sourced sediments in addition to fluvial input. However, potential Old Yellow River (OYR) contributions, from when it discharged into the Yellow Sea over the last 1,000 years, remain unclear. Here we present provenance results of three cores from the northern YRD using size-specific magnetic characterization. Each core contains prodelta, delta front and delta plain facies in ascending order. We found that magnetic properties of bulk samples are strongly influenced by particle size and diagenesis, with sediments younger than ~400 years are least influenced by diagenesis, and therefore we focused provenance assessment on this period. Comparison of magnetic properties to potential sources, i.e., Yangtze and OYR sediments, indicates that the northern core received enhanced Yellow River sediment loads over the last 400 years, while the southern core had a dominant Yangtze influence. Such a spatial heterogeneity in sediment source is most pronounced in the fractions less than 32 um. Our results imply that YRD deposits cannot be ascribed solely to Yangtze River inputs. Both riverine and marine-sourced sediments should be assessed when forecasting tidal-dominated delta evolution under a condition of declining fluvial sediment load in the Anthropocene.