Sedimentary records of the Yangtze Estuary over the past 70 years and their implications for provenance

Abstract

The Yangtze River is the largest river in southern China. In this study, the two sediment cores (CM-A and NH-C) taken from the Yangtze River Estuary were analyzed for 210Pb and 137Cs dating, major and trace elements, rare earth elements (REEs) and grain size of sediments. The results showed that the sedimentary ages of CM-A and NH-C cores were 37 and 64 years respectively. Then the major and trace elements in the sediments of the Yangtze Estuary were derived from terrigenous clastic materials. The chemical index of alteration (CIA) in the two cores ranged between 57 and 70, 66 and 73, respectively, reflecting the low to intermediate intensity of chemical weathering in the provenance area. The abundance of heavy minerals, grain size in hydrodynamically sorted, and chemical weathering have less effect on REE chemistry in the core CM-A, as well as the source of sediments in the core CM-A can be identified. By comparing the geochemical elements of sediments from the Yangtze River Basin, The provenance of sediments in the upper reaches of the Yangtze River might be similar to those of core CM-A sediments. Combined with A-CN-K and La-Th-Sc ternary diagrams and source discrimination diagrams of REEs parameters, it was presumed that the samples were influenced by K metasomatism, and originated from the same source area, and the granodiorite was the most probably source rock of these samples. Therefore, the upper reaches of the Yangtze River are considered to be the main source area of the sediments core CM-A.