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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) | Year: 2013

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.

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.
Sedimentology | Year: 2013

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.

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 | Year: 2013

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.

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 | Year: 2013

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.

Wang Z.,East China Normal University | Li M.,East China Normal University | Zhang R.,East China Normal University | Zhuang C.,East China Normal University | And 4 more authors.
Holocene | Year: 2011

Development of the Yangtze delta during the late Holocene, and its relationship to human activities in the drainage basin, was analyzed using data from 16 cores collected from distributaries to the prodelta. We used AMS 14C dating and digital elevation model (DEM) data from marine charts from 1864 through 2005 to determine ages and estimate sediment accumulation rates. The results demonstrate that the latest major subaqueous delta front formed within the past c. 0.8 cal. ka and features remarkably high accumulation rates (1-4 cm/yr) in comparison with those of previous delta fronts. We also examined the temporal distribution of grain size and magnetic susceptibility in all 16 cores. Results show soil-derived superparamagnetic (SP) minerals generally occur, and even dominate, in the recent (c. 1.7 cal. ka) Yangtze delta fine-grained sediment, as shown by high values of frequency-dependent magnetic susceptibility (both χFD and χFD%). Rock-derived magnetite dominates generally in the river channel and delta front sand bodies as a result of hydrodynamic sorting, but is also enriched in both fine and coarse-grained sediment formed more recently (c. 0.8 cal. ka), as evidenced by rising values of mass specific magnetic susceptibility (χLF). SP grains were deposited as early as the late Neolithic, possibly indicating local deforestation associated with the use of fire at that time. We suggest major deforestation in the drainage basin started c. 1.7 cal. ka BP, and intensified after c. 0.8 cal. ka BP when both χLF and χFD show the highest values. We therefore conclude that upland deforestation and cultivation as a result of the migration of human populations from northern China since c. 1.7 cal. ka BP resulted in increased sediment discharge of the Yangtze and played an important role in recent delta construction. © The Author(s) 2010.

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.
Holocene | Year: 2015

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.

Wang Z.,East China Normal University | Xu H.,East China Normal University | Zhan Q.,East China Normal University | Saito Y.,Geological Survey of Japan | And 4 more authors.
Quaternary Research | Year: 2010

AMS 14C ages of post-glacial core sediments from the subaqueous Yangtze delta, along with sedimentary structures and distributions of grain size, pollen spores, and dinoflagellate cysts, show an estuarine depositional system from 13 to 8.4cal ka BP and a deltaic system from 5.9cal ka BP to the present. The estuarine system consists of intertidal to subtidal flat, estuarine, and estuarine-front facies, characterized by sand-mud couplets and a high sedimentation rate. The deltaic system includes nearshore shelf and prodelta mud featured by lower sedimentation rate, markedly fewer coastal wetland herbaceous pollens, and more dinoflagellate cysts. We explain the extremely high sedimentation rate during 9.2-8.4cal ka BP at the study site as a result of rapid sea-level rise, high sediment load due to the unstable monsoonal climate, and subaqueous decrease of elevation from inner to outer estuary. A depositional hiatus occurred during 8.2-5.9cal ka BP, the transition from estuarine to deltaic system, caused possibly by a shortage of sediment supply resulting from delta initiation in paleo-incised Yangtze valley and strong tidal or storm-related reworking in offshore areas. The subsequent development of deltaic system at the study site indicates accelerated progradation of Yangtze delta post-5.9cal ka BP. © 2009 University of Washington.

Zhan Q.,East China Normal University | Wang Z.,East China Normal University | Xie Y.,East China Normal University | Xie J.,Shanghai Geological Survey | He Z.,Shanghai Geological Survey
Holocene | Year: 2012

To examine the applicability of C/N and organic carbon stable isotope (δ13C) in studies of the Holocene sea level and freshwater discharge in the large river mouth of Yangtze, we observed the distribution of carbon, nitrogen and δ13C in a late-Quaternary core (ZK9) collected from the present subaqueous delta. We also collected published data of the two proxies for the suspended particulate matter (SPM) and surficial sediments from the lower Yangtze River to the adjacent East China Sea. The results show that the estuarine front is an important boundary for terrestrial and marine contribution of the organic component in the modern sedimentary environment. In the core ZK9, sediments deposited during c. 13-9 cal. ka BP are characterized by high values of TOC (0.54-1.16%), CaCO3 (0.35% on average), and C/N (>12), which reflect an inner tidal estuarine environment dominated by C3 terrestrial organic carbon input. During c. 9-0.7 cal. ka BP, both TOC content (0.57% on average) and C/N ratio (<10) decrease remarkably while TN increases, indicating a lower estuarine or shallow marine environment. An abrupt sea level rise from c. 9 cal. ka BP resulted in a deeper water environment and reduced terrestrial input at the core location. The low δ13C values (-24.23‰ on average) before c. 6 cal. ka BP reflect a dominantly terrestrial source of organic matter associated with increased freshwater discharge into the estuary during that time. The sediments since c. 6 cal. ka BP are characterized by increasing δ13C up to -24.1 to -23.39‰, reflecting more contribution from marine algae as freshwater discharge fell. We suggest that in the Yangtze River mouth the C/N ratio indicates an abrupt sea level rise at c. 9 cal. ka BP, while δ13C is more useful in reflecting freshwater discharge. © The Author(s) 2011.

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