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As the largest river of China, the Yangtze River transports large amounts of sediments to the adjacent oceans. Provenance of these ancient marine sediments can only be deciphered when the source-to-sink process of modern sediments in the Yangtze River is fully understood. Many methods have been used to study the provenance of river sediment and an environmental magnetic method is applied in this study because of its fast, nondestructive advantages. Magnetic properties of suspended particulate matter (SPM) along the Yangtze River were measured to provide a holistic understanding about magnetic properties of sediments in this river and its controlling factors. The results indicate that the dominant magnetic mineral in SPM is magnetite, with a small contribution of hematite and goethite. Significant spatial variation was observed in most of the magnetic parameters, which primarily reflects the distribution of major geologic units along the drainage area of the river. Anthropogenic influences are also recorded in the magnetic parameters. The Three Gorges Dam results in a dramatic decrease of magnetic minerals in the downstream reaches, since its construction in 2003. In addition, small variations in magnetic properties of SPM are found along water depth, together with a clear seasonal shift at Datong station. This seasonal variation of magnetic properties of SPM is driven by variability in both hydrology and source contributions. This complicates the use of magnetic parameters for provenance studies. Magnetic properties of sediments in rivers are capable of tracing provenance areas, but caution must be taken into account. [ABSTRACT FROM AUTHOR]

This study examines the effects of hydrologic sorting and mixing of sources on the Sr-Nd isotopic compositions of suspended sediments at different water depths. The samples were collected from three layers (surface, middle and bottom) at Datong hydrological station of Yangtze River during the flood season of 2010. Our results show that, Sr/Sr values decrease from surface to bottom, ranging from 0.730332 to 0.720857. ɛ(0) values range from −14.75 to −10.09, with surface sediments being the most negative. The isotope composition at the middle layer can best represent the mean isotopic composition of the total suspended sediments transported by a river. It is believed that the stratification of Sr-Nd isotope is attributable to mixing of sediments from different sources due to hydrological sorting. Sediments from the upper stream are found to be coarser, and tend to contribute more to the lower water column. Although Sr-Nd isotope is a well acknowledged tool to trace sediment provenance, the current study suggests that the grain size of the samples and the sampling locations should be taken into consideration when applying this method to provenance study. [ABSTRACT FROM AUTHOR]

Volcanic rocks, black shales, calcareous sandstones and cherts occur in the Wufeng and Longmaxi formations, which cross late Katian through Rhuddanian exposed along the northern and central part of the Yangtze block, South China. The evidence provided by radiolarite occurrences, sedimentological features and immobile elements indicate that the silica in these rocks is sedimentary and not of hydrothermal origin. Precursors of chert were deposited on a continental margin, or in a deeper basin on the shelf, during blooms of radiolarians and times of decreased clastic input. Interbedded volcanic tuffs of rhyolitic to andesitic composition suggest the presence of a continental volcanic arc to the east–southeast. The large regional extent of bentonites documents explosive volcanicity resulting in silica saturation of waters, leading to high bioproductivity and radiolarian blooms. Deepening of the sedimentary environment is most probably the result of orogenesis generated by an accretion of the Cathaysia Block to the Yangtze Block during the Ordovician–Silurian transition. Increasing water depth together with a decrease in clastic input contributed to the development of the radiolarian cherts in the basin. [ABSTRACT FROM AUTHOR]