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Shanghai, China

Liu Y.,East China Normal University | He Z.,Shanghai Geological Survey | Wang Z.,State Key Laboratory of Estuarine and Coastal Research
Frontiers of Earth Science

We measured the magnetic properties of core ZK9 from the subaqueous Yangtze delta to examine the mechanisms and possibility of using magnetic proxies for the sedimentary environmental evolution controlled by the Holocene sea level. The results showed that low values of most magnetic parameters occurred and pyrite formed in the estuarine sediments during c. 10.5-8.4 cal ka BP, reflecting the predominant early diagenesis in a tidaldominated depositional environment when the sea level rose rapidly. Sharp increases in the values of χ ARM (susceptibility of Anhysteresis Remanent Magnetisation), χ ARM/χ, χ ARM/SIRM (Saturation Isothermal Remnant Magnetisation) and HIRM (Hard Isothermal Remnant Magnetisation) occurred immediately above the transitional zone from estuarine to deltaic system of c. 8.4-5.9 cal ka BP, which imply accumulation of single-domain magnetite and anti-ferromagnetic minerals. These magnetic properties indicate the enhanced freshwater processes at the core site as a result of the relatively stable sea level and the associated delta progradation since c. 5.9 cal ka BP. Therefore, magnetic proxies of χ ARM and HIRM are useful to identify the maximum flooding surface. In addition, the intertidal-subtidal sediment of c. 13.2-10.5 cal ka BP had high values of χ, SIRM and HIRM, reflecting the features of a coastal environment. The sharp decline of the above parameters from c. 10.5 cal ka BP indicates possibly an event of rapid sea level rise. © 2013 Higher Education Press and Springer-Verlag Berlin Heidelberg. Source

Wang Z.,East China Normal University | Zhan Q.,Shanghai Geological Survey | Long H.,Ocean University of China | Saito Y.,Geological Survey of Japan | And 4 more authors.
Journal of Quaternary Science

We used accelerator mass spectrometry (AMS) 14C-dated sediments of the Holocene basal supratidal flat to upper tidal flat facies in 11 cores on the southern Yangtze delta plain to reconstruct relative sea levels of 8.5-8.0 cal ka BP. Three cores were further AMS 14C dated and used to examine the evolution of sedimentary geomorphological environments in response to the rapid sea-level rise during the early to mid-Holocene. Results demonstrate relative sea-level rise of around 30mm a-1 from 8.5 to 8.3 cal ka BP and around 10mm a-1 from 8.3 to 8.0 cal ka BP. Retrogradation from supratidal to lower tidal flat environments occurred in response to the rapid sea-level rise at 8.5-8.3 cal ka BP, and aggradation from middle to upper tidal flat occurred at 8.3-7.9 cal ka BP. Further retreat of the tidal flat at 7.9-7.2 cal ka BP implies a mean sea-level rise rate exceeding 5mm a-1 at this time. We suggest that the rapid relative sea-level rise during 8.3-8.5 cal ka BP and subsequent slower rise caused drastic changes in the coastal zone and that these changes are key phenomena for understanding the coastal response to future sea-level rise. © 2013 John Wiley & Sons, Ltd. Source

Chen T.,East China Normal University | Wang Z.,East China Normal University | Wu X.,East China Normal University | Gao X.,East China Normal University | And 2 more authors.

Measurements of magnetic properties, total organic carbon (TOC) and total sulphur (TS) were performed on recent tidal flat sediments from the Feng-Xian (FX) and Bei-Bu-Gang (BBG) areas of the Yangtze coast and on Holocene tidal flat sediments from core SL67 from the southern Yangtze delta plain, China. The results indicate that greigite has likely formed in the recent upper and middle tidal flat sediments of cores FX and BBG, which are enriched in TOC and TS. Greigite is also present in association with pyrite in the early to middle Holocene saltmarsh and tidal flat sediments of SL67. The abundance of greigite in the early Holocene basal saltmarsh sediments of core SL67, along with the extremely low values of TS/TOC, suggest the presence of either a limited sulphate supply from seawater or a major terrestrial source of organic matter that decomposed slowly. The presence of greigite in mid-Holocene lower tidal flat sediments that contained low amounts of TOC indicates an upward diffusion of CH4 and H2S from the underlying upper tidal flat sediments. A comparison between the sediments of core SL67 and those of the modern tidal flat suggests that early diagenesis (including selective dissolution and pyritisation) continued after the sediments were buried during the Holocene, resulting in the depletion of soil-derived superparamagnetic (SP) particles and the enhanced magnetic properties because of authigenic greigite. However, antiferromagnetic magnetic minerals have not been altered by early diagenesis. Thus, magnetic parameter hard isothermal remanent magnetisation (HIRM) which preserved the primary magnetic signals reflects fluctuations in the detrital mineral input to the core site and records a two-stage 8.2 ka cooling event. © The Author(s) 2015. Source

Wang Z.,East China Normal University | Jones B.G.,University of Wollongong | Chen T.,East China Normal University | Zhao B.,Shanghai Geological Survey | Zhan Q.,Shanghai Geological Survey
Quaternary Research (United States)

The distribution of marine-influenced oxygen isotope stage (OIS) 5 to OIS 1 sediments was examined in several late Quaternary boreholes from the southern Changjiang (Yangtze) delta plain, China, using different dating methods including OSL, U-series, AMS 14C and paleomagnetism. Results demonstrate that coastal and estuarine deposition during OIS 5 and OIS 3 occurred throughout the study area. However, Holocene transgressive sediments were absent on the Taihu block. The burial depth of intertidal to subtidal sediment deposited during OIS 5e records 30-80m subsidence caused by sediment compaction and tectonic movement since that time. However, coastal sediments formed during the late phase of OIS 3 were buried to a depth of ca. 6-15m in the Taihu Lake area, while the burial depth increased eastward to ca. 45-60m on the coastal plain. This phenomenon, combined with the distribution of Holocene marine strata, indicates at least 25-30m uplift of the Taihu block since the end of OIS 3. We suggest that this uplift was mainly caused by the differential subsidence due to substantial amount of post-glacial deposition by the Changjiang and Huanghe Rivers on the continental shelf of east China marginal sea. © 2013 University of Washington. Source

Wei T.,East China Normal University | Wei T.,University of Leeds | Peakall J.,University of Leeds | Parsons D.R.,University of Hull | And 3 more authors.

The nature of three-dimensional flow in submarine channel bends is poorly understood, largely due to the absence of detailed data from natural channels. Herein, data from density-driven flows in a large reservoir on the Huanghe (Yellow) River are presented showing the spatio-temporal variation of flow around a subaqueous bend. The data demonstrate for the first time that reversed helical flow, relative to that found in river channel bends, can occur from the centrifugal forcing of flow, even when the Coriolis force acts in the opposite direction. The data also suggest that reversed helical flow fields in submarine channels may be more frequent than currently estimated, notably for bends where Coriolis and centrifugal forces combine in the same direction. In addition, this study provides the first field evidence suggesting that sinuous submarine channels can exhibit an asymmetry in helical flow orientation between left and right-turning bends, which will have major implications for the morphodynamics of submarine channels, their resultant patterns of sedimentation and, ultimately, the distribution of depositional units across submarine fan systems. © 2013 The Authors. Journal compilation © 2013 International Association of Sedimentologists. Source

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