Shouye Yang

A review on the provenance discrimination of sediments in the Yellow Sea

The Yellow Sea has been extensively studied for the understanding of dispersal patterns and limits of sediments from neighboring countries including China and Korea. Although sedimentological, mineralogical, and geochemical approaches have been tried to solve the problems, especially including the identification of sediment sources in and around the Yellow Sea, the published results are not enough for understanding them. Suggestions on sediment origins, budgets, sediment accumulation rates, mineralogical, and geochemical compositions are not coincident to each other and sometimes even controversial; for example, conflicts on the distribution patterns of smectite and calcium carbonate, the provenance of the southeastern Yellow Sea mud and sedimentation rates in there, the ratios of V/Al and Mn/Al in Korea and China river sediments, the origin of Ba and Pb in sandy sediments of the northeastern Yellow Sea, and so on. Various geochemical indicators from the literature for the provenance discrimination in the Yellow Sea are reviewed here in depth, and corresponding discussions are described separately. Research topics for the future study, also, are suggested for the proper access to the understanding of the origin and dispersal patterns of the Yellow Sea sediments, especially focusing on the geochemical approaches. D 2003 Elsevier Science B.V. All rights reserved.

The rare earth element compositions of the Changjiang (Yangtze) and Huanghe (Yellow) river sediments

Thirty-four samples from the Changjiang and Huanghe were analyzed to characterize their rare earth element (REE) compositions. Although REE concentrations in the Changjiang sediments are higher than those of the Huanghe sediments, the former are less variable. Bulk samples and acid-leachable fractions have convex REE patterns and middle REE enrichments relative to upper continental crust, whereas flat patterns are present in the residual fractions. Source rock composition is the primary control on REE composition, and weathering processes play a minor role. Grain size exerts some influence on REE composition, as demonstrated by the higher REE contents of clay minerals in sediments from both rivers. Heavy minerals contribute about 10^20% of the total REE in the sediments. Apatite is rare in the river sediments, and contributes less than 2% of the REE content, but other heavy minerals such as sphene, allanite and zircon are important reservoirs of residual REE fractions. The Fe^Mn oxides phase accounts for about 14% of bulk REE content in the Changjiang sediments, which could be one of the more important factors controlling REE fractionation in the leachable fraction. 6 2002 Elsevier Science B.V. All rights reserved.

Stratigraphy and paleoenvironmental changes in the Yangtze Delta during the Late Quaternary

The Yangtze Delta area may be subdivided into paleo-valley and paleointerfluves of the last glaciation. The postglacial transgressive sedimentary cycle (PTSC) on the front zones of the paleointerfluves is composed of marsh-nearshore and barrier-lagoon, shallow marine and nearshore-tidal flat units, with a basement in stiff clay. The PTSC in back zones of the paleointerfluves consists of lacustrine-marsh deposits. The PTSC in the incised valley contains river channel, floodplain-estuary, estuarine-shallow marine and deltaic units, with an erosional surface at its bottom. The stiff clay and the erosional surface constitute the PTSC lower boundary. The stiff clay, consisting of a paleosol, experienced deposition alternating with pedogenesis during the falling of sea-level during δ18O stage 3; ongoing pedogenesis in the sea-level lowstand of δ18O stage 2; and early diagenesis after paleointerfluve inundation by the sea-level rise of δ18O stage 1. The climate during the paleosol formation was temperate with more than 500-mm a−1 rainfall and frequently fluctuating groundwater. The Yangtze River incised its course during falling sea level of stage 3, and a huge incised valley was formed during the sea-level lowstand (stage 2). The filling of the incised valley took place during the postglacial sea-level rise, and delta formation occurred at a late stage of PTSC development.

Distribution, enrichment and source of heavy metals in surface sediments of the eastern Beibu Bay, South China Sea

Sixty-nine samples of surface sediments (0-5 cm) recovered from the eastern Beibu Bay were analyzed for TOC and heavy metals to examine the element distribution pattern and potential pollutant sources. The sediments in the study area are characterized by variable heavy metal concentrations that are comparable with those of the surrounding regions. Obvious positive correlations were observed amongst the concentrations of Zn, Cr, Pb, Cd, Cu and the clay contents, suggesting that fine clay particles are important carriers of trace metals in the sediments. Hg and As show a considerable/low positive correlation with TOC, indicating that organic matter may play a discernible role in the sediment chemistry. Cd contamination was detected in the north of the study area primarily due to the input of phosphate fertilizers carried by rivers. In comparison, Zn, Cr, Pb, and partly Cu are predominantly sourced from lithogenic components, and Hg and As are mainly from organic matter related to anthropogenic input.

Chemical weathering of the loess deposits in the lower Changjiang Valley, China, and paleoclimatic implications

Abstract Loess deposits (Xiashu Loess) are widely distributed in the lower Changjiang Valley, East China, and are considered to be of eolian origin with a similar provenance to the well-documented loess of north-central China. The Xiashu Loess is characterized by strong dissolution of carbonate, and considerable weathering of some silicate minerals, especially plagioclase. Chemical mobility of Ca>Sr>Na>Mg was observed in the Xiashu Loess sediments, whilst most transition metals are relatively enriched. Chemical index of variation (CIA) and element ratios of K/Na and K/Ca record several paleoclimate events in the lower Changjiang Valley during the mid-late Quaternary, corresponding with isotopic records in deep-sea sediments. East China might be governed by stronger summer monsoons than north-central China during interglacial periods of the mid-late Quaternary, which may somewhat obscure the record of winter monsoons during glacial periods.

Discrimination of geochemical compositions between the Changjiang and the Huanghe sediments and its application for the identification of sediment source in the Jiangsu coastal plain, China

Concentrations of 25 elements in the fine-grained fraction (6 63 Wm) of bottom sediments of the Changjiang and the Huanghe were determined to characterize the geochemical compositions of each riverine origin. Most of the elements, except for alkali and alkaline earth elements (Na, Ca, Sr and Ba), are highly enriched in the Changjiang sediments compared to those in the Huanghe sediments. Differences in source rocks and weathering mechanisms between the two drainage basins are the major factors controlling those compositional characteristics. The provenance index of core sediments from the northern Jiangsu coastal plain, calculated with nine elements with distinct compositional differences between both river sediments, indicates that the Changjiang had prevailed in the coastal plain sedimentation during the early stage of Holocene, while the Huanghe dominated over the area during the late Holocene. However, neither of the signatures of the modern Changjiang- and Huanghe-derived sediments is remarkable in the present-day coastal plain. 5 2002 Elsevier Science B.V. All rights reserved.

IS CHEMICAL INDEX OF ALTERATION (CIA) A RELIABLE PROXY FOR CHEMICAL WEATHERING IN GLOBAL DRAINAGE BASINS

The chemical weathering of silicate rocks in continents as an important sink of atmospheric CO2 is of great significance for global environmental change. Rivers play a key role in earth surface processes and are regarded as the most important carrier of terrigenous materials into the sea. The chemical index of alteration (CIA) has been widely used as a proxy for chemical weathering in sediment source area. In this paper, the CIA values of suspended particulate matters from 44 rivers worldwide are recalculated. The CIA values vary significantly, with the highest average value occurring in African rivers and the lowest in North American rivers. The correlation analyses suggest that on a global scale the CIA is sensitive to land surface temperature, latitude at river mouth and soil depth in the drainage basins, but poorly correlated with drainage area, precipitation, average elevation and runoff. However, the CIA of the rivers draining east China are closely related to temperature, precipitation, latitude and runoff, primarily reflecting the dominant control of monsoon climate on chemical weathering in the catchments. It is therefore unrealistic to find a simple law of regulating chemical weathering in continents. The CIA actually reflects the integrated weathering history in the drainage basins and therefore, caution should be taken while using it as a direct and quantitative proxy for evaluating the intensity of instantaneous chemical weathering in continents.

Heavy metal enrichments in the Changjiang (Yangtze River) catchment and on the inner shelf of the East China Sea over the last 150 years

Compositions of heavy metals including Cu, Zn, Cr and Pb in three sediment cores recovered from the lower basin of the Changjiang (Yangtze River) and the inner shelf mud of the East China Sea were analyzed by traditional X-ray florescence (XRF) and XRF Core Scanner. This study aims to investigate the accumulation of heavy metals in the fluvial sediments and to decipher the influence of anthropogenic activities within the large catchment over the last 150 years. The data suggest that the heavy metals, especially Pb and Zn, show obvious enrichments in concentrations since 1950s, and the small and consistent variations of heavy metal concentrations before 1950s can represent geochemical background values. After removing the grain size effect on elemental concentrations, we infer that the sources of heavy metals predominantly come from natural weathering detritus, while human contamination has increased over the last half century. The calculations of both enrichment factor and geoaccumulation index, however, indicate that the pollution of these heavy metals in the fluvial and shelf environments is not significant. The rapid increase in human activities and fast socioeconomic development in the Changjiang catchment and East China over the last five decades accounts for the enrichments of heavy metals in the river and marine sediments. The inner shelf of the East China Sea, as the major sink of the Changjiang-derived fine sediments, provides a high-resolution sediment archive for tracing the anthropogenic impacts on the catchment.

Characteristic and paleoenvironmental evolution of subaerial tidal sand body in Subei coastal plain

The subaerial tidal sand area in the northern Jiangsu Province (Subei), stretching from Dongtai towards east with a fan shape, is an early developing stage of radial sand ridges distributed in the South Yellow Sea. Since 5000–6000 a BP, after the Holocene transgression maximum in the northern Jiangsu Province, subaqueous tidal sand bodies were exposed and changed into land gradually. The environmental magnetism analysis shows that subaerial tidal sand strata are formed by the convergent-divergent paleo-tidal current field. The sediment source of tidal sand strata came early from the Changjiang River and late from the Yellow River. Sea floor erosion by tidal currents also served as an important sand source. Drilling cores and ground-penetrating profile show that there exists no probability of sand supplying directly by a large river through the apical area of tidal sand ridges either on land or in the sea. Fluvial deposits supplied the tidal sand bodies by alongshore transportation, which corresponds to the conclusions obtained by the analyses of provenance and paleocurrent field.

REE geochemistry of suspended sediments from the rivers around the Yellow Sea and provenance indicators

Rare earth element (REE) compositions of the suspended sediments from the rivers around the Yellow Sea were different in that Korean river sediments (Han, Keum and Yeongsan Rivers) yield stronger fractionations than Chinese river sediments (Changjiang, Huanghe and Yalujiang), shown by obvious enrichments of LREE (light rare earth element) relative to UCC (upper continental crust). Variations of source rock compositions in the drainage basins are responsible for the differences of REE compositions between the river sediments. REE fractionation parameters including (La/Yb)UCC and (Gd/Yb)UCC as well as the ratios of La/Sc and Th/Sc can be treated as proper proxies for identifying the Chinese river sediments from those Korean river matters, and furthermore, for studying the provenances and paleoenvironmental changes of the marginal seas of China.