Kunshan Wang

Late Quaternary sedimentary environmental evolution offshore of the Hangzhou Bay, East China—implications for sea level change and formation of Changjiang alongshore current

This study focuses on sedimentary environmental changes offshore of Hangzhou Bay, East China, since the Late Quaternary. AMS 14C ages from core CJK10, lithologies, distribution of foraminifera, heavy minerals, and S and Cl elements show a fluvial terrace environment during ∼23.2–11.0 cal ka BP; a littoral to tidal-flat environment during 11.0–10.2 cal ka BP; and a shallow marine environment with a relatively low sedimentation rate (0.1–0.22 cm/a) since 4.3 cal ka BP. High depositional rates (∼1.6 cm/a) from 10.9 to 10.2 cal ka BP resulted from sufficient accommodation space created by rapid sea level rise from −44 m to −33 m, from high sediment delivery by local rivers, and effective trapping of sediments by tidal-flat vegetation. The rate of sea level rise was variable; relatively high from 10.9 to 10.6 cal ka BP (2.1 cm/a), and lower since 10.6 cal ka BP (1.2 cm/a). The Changjiang alongshore current crossed the Hangzhou Bay to form the mud wedge on the inner shelf of the East China Sea later than 9.4 cal ka BP. The CJK10 site was a tide-dominated shelf environment and experienced erosion from approximately 9.4-9.2 cal ka BP to 4.3 cal ka BP. The depositional hiatus was caused by the Changjiang alongshore current, which was relatively weak during 9.4-7.5 cal ka BP and increased in strength during ∼7.5-4 cal ka BP. From ∼4.3 cal ka BP, a large amount of sediment from the Changjiang River was partly deposited on the continental shelf of Hangzhou Bay with some transported southward. Therefore, this study clarifies the history of Changjiang-derived sediment dispersal and deposition, although a detailed record of the changes in the Changjiang alongshore current since 4.3 cal ka BP is difficult to obtain because of the scarcity of evidence.

The distribution and variation of elements in sediments off the Huanghe (Yellow) River mouth

Surface sediment samples collected off the Huanghe (Yellow) River mouth during the period 2007–2009 were analyzed for major and trace element concentrations. Concentrations of 16 elements were measured using X-ray fluorescence spectrometry. Results demonstrate that sediment grain size is the dominant factor controlling the spatial variations of elemental concentrations. Correlation and cluster analyses allowed classification of the study area into four geochemical regions: Regions I and III are characterized by high concentrations of Al2O3, Fe2O3, MgO, Na2O, K2O, Cr, Cu, Mn, Ni, Pb, V, and Zn, and contain fine-grained sediments with mean grain size (Mz)<22 μm; and; Regions II and IV contain mostly coarse-grained sediments, and are characterized by high concentrations of SiO2, Na2O, and Zr. The sediment entering the sea from the Huanghe River and its tributaries is enriched in Ca. Thus, the Ca/Al ratio was used as an indicator of the proportion of sediments in the study area that originated from the Huanghe River. Ca/Al ratios decrease from Regions I and II (located in the nearshore zone of the Huanghe River delta) to Regions III and IV (distributed in the offshore zone of the northern Huanghe River delta, southern and southeastern Laizhou Bay area).

THE COLOR REFLECTANCE FEATURES OF THE SEDIMENTS IN MUD AREA ON THE INNER SHELF OF THE EAST CHINA SEA AND ITS PALEOCLIMATIC IMPLICATIONS FOR RECENT 2 ka: THE COLOR REFLECTANCE FEATURES OF THE SEDIMENTS IN MUD AREA ON THE INNER SHELF OF THE EAST CHINA SEA AND ITS PALEOCLIMATIC IMPLICATIONS FOR RECENT 2 ka

A climatic proxy system is constructed on the basis of the color reflectance data of the core MZ01 using first derivative and factors analysis method,and a high-resolution climatic sequence is established with the support of AMS14C dating data for the past 2 ka.900AD is the key turning-point in the course of climate evolution.Climate became significantly cold with high-frequency but low amplitude temperature fluctuation right after 900AD.In the past 2 ka,the climate in East China has experienced four stages including a cold stage before 580AD,a warm stage between 580 and 900AD,a temperature fluctuation stage between 900 and 1460AD and a cold stage between 1460 and 1880AD.Each stage includes some secondary regional or global temperature fluctuations.

DISTRIBUTION AND SOURCE OF HEAVY MINERALS IN THE SURFACE SEDIMENT OF THE TIDAL SAND RIDGES AREA IN SOUTH YELLOW SEA

A total of 301 surface samples collected in 2008 from the tidal sand ridges area located to the south of the abandoned yellow river subaqueous delta in the south yellow Sea were analyzed for heavy minerals.Some distinct characteristics of heavy minerals are observed in the study area:(1)the high weight content of heavy minerals;(2)abraded mineral grains and iron-stained grain surface;and(3)sharp content variation in dominant minerals from area to area.These characteristics were dependent upon the depositional environment which was featured by strong hydrodynamics,high content of sand fraction,strong oxidation,and quick variation in water depth in the sand ridges area.Common hornblende and epidote dominate.Mica,hematite,limonite,ilmenite and magnetite are recognized as diagnostic minerals.The mineral assemblages suggest that the source would be the dominant factor controlling the distribution pattern of heavy minerals.The sediments of the tidal sand ridges area are mainly from the Yellow River and the Yangtze River.The contribution of other material sources is not obvious.The materials from the Yellow River are widely distributed in the whole tidal sand ridges area.However,its impact gradually becomes weak form north to south.By contrast,the materials of Yangtze River are mainly distributed in the middle and southern parts of the tidal sand ridges area.The distribution of stable minerals,especially zircon could be used to denote the distribution area of the materials from the Yangtze River.The content of heavy minerals and their spatial distribution demonstrate that high oxidation and severe erosion mainly occur in the outer part of tidal sand ridges area.There is no obvious differentiation of mineral composition between the sand ridges and the adjacent areas,showing that sand ridges are in the process of shrinking.The distribution of schistose minerals and weathering index indicate that there might be a path for sediment dispersion from the abandoned Yellow River subaqueous delta to the northeastern of Yangtze River mouth passing through the middle part of the tidal sand ridges area.

Distribution and composition of authigenic minerals in surface sediments of the western Gulf of Thailand

Generation, morphology, and distribution of authigenic minerals directly reflect sedimentary environment and material sources. Surface sediments were collected from the western Gulf of Thailand during 2011–2012, and 159 samples were analyzed to determine detrital minerals. Authigenic minerals, including siderite, pyrite, and glauconite, are abundant whereas secondary minerals, such as chlorite and limonite, are distributed widely in the study area. Siderite has a maximum content of 19.98 g/kg and appears in three types from nearshore to continental shelf, showing the process of forming-maturity-oxidation. In this process, the MnO content in siderite decreases, but Fe2O3 and MgO content increase. Colorless or transparent siderite pellets are fresh grains generated within a short time and widely distributed throughout the region; high content appears in coastal area where river inputs are discharged. Translucent cemented double pellets appearing light yellow to red are mature grains; high content is observed in the central shelf. Red-brown opaque granular pellets are oxidized grains, which are concentrated in the eastern gulf. Pyrite is mostly distributed in the central continental shelf with an approximately north–south strip. Pyrite are mainly observed in foraminifera shell and distributed in clayey silt sediments, which is similar to that in the Yangtze River mouth and the Yellow Sea. The pyrite in the gulf is deduced from genetic types associated with sulfate reduction and organic matter decomposition. Majority of glauconite are granular with few laminar. Glauconite is concentrated in the northern and southern parts within the boundary of 9.5° to 10.5°N and is affected by river input diffusion. The distribution of glauconite is closely correlated with that of chlorite and plagioclase, indicating that glauconite is possibly derived from altered products of chlorite and plagioclase. The K2O content of glauconite is low or absent, indicating its short formation time.

MINERALOGY OF SURFACE SEDIMENT IN THE EASTERN AREA OFF THE RYUKYU ISLANDS AND ITS GEOLOGICAL SIGNIFICANCE

The mineral composition of the bulk samples of the surface sediment in the eastern area off the Ryukyu Islands is studied with X-ray diffraction(XRD).It is found that the sediment consisting of smectite,illite+mica,kaolinite+chlorite,quartz,potash feldspar,plagioclase and calcite,is dominated by quartz,illite+mica,calcite and plagioclase,and kaolinite+chlorite and smectite occupy the second place with potash feldspar occasionally observed.According to the mineral composition,it is deduced that the sediment came from terrigenous,volcanic and biogenic sources.

Sedimentary Facies and Material Source of Core DGKS9617 in the East China Sea

A piston core DGKS9617, recovered from the northern part of the inner shelf of the East China Sea (ECS) is divided into two sedimentary facies: a tidal shallow marine facies (55-850 cm) and a shallow marine facies (0-55 cm). Although the sedimentary environments of its upper and lower parts are different, the provenance of the whole core does not change. The heavy mineral assemblage, the results of the discrimination function of Fe, Mn, V, Cr, Ni, Cu and Zn, the carbonate content and the Ba-Sr-Zn ternary diagram consistently show that the heavy mineral and geochemical characteristics of core DGKS9617 are similar to that of the Yangtze River sediments and that its sediment is mainly provided by the Yangtze River.