Modern Sedimentary Environment Research On The Radial Sand Ridges Off Jiangsu Coast

Based on Folk classiifcation method, four type of surficial sediment can be found in the studyarea, they are: sand, silt-sand, sand-silt and silt. The surficial sediment on ridges is sand orsilt-sand, while the surifcial sediment in channels is mainly sand-silt, A large patch ofsilt exist between the radial sand ridges and the abandoned Yellow irver estuary. Thevariation of particle spectra of sediment in study area indicate it is a mixing product ofseveral peaks, which may have different provenance due10complex sedimentaryhistory. To reveal the scdimcni Iran sporting mechanism between abandoned Yellow""river delta and radial sand ridges, End Member Model and grain size trend analysismodel have been employed to distinguish the '"dynamic subpopulations" in surfacesediment particle spectra and to determine the possible sediment transporting pathway.Th"e results reveal four "dynamic subpopulations (HM1to HM4) and two reversesediment transporting directions: a northward transport tend from the radial sandridges to mud patch, and a southward transport trend in the deep water area out ofmud patch. Combined with the published hydrodynamic information, the transportingmechanism of dynamic populations have been discussed, the main conclusion is: thetranspotring of finer subpopulations EMI and EM2are controlled by the^anticlockwise residual current circulalion" forming during tidal cycle, which favor anorthward transporting trend and the forming of mud patch on the north of radial sandHdgcsT while the transpotring of coarser HM3is mainly controlled by wind drivendritf in winter, which favor a southward transporting direction.During a cruise of May list to June4th in200S, water sampling and in situgrain size distribution detecting (by a L1SST-100X) have btxn deployed at411bitesin the area of radial sand ridges local off JiangSu coastline of China. Mainly based onthe data of suspended sediment concentration (SSC) and in situ suspension particlespectra, the characteristic and mechanism of sea bed sediment resuspending anddiffusion in this area have been analyzed. The main conclusions are summarized as below:(1) in this area, the predominant characteristic of SSC spatial distribution isthe existence of turbid plume along coastline which extend from abandoned YellowRiver estuary to the the center area of radial sand ridges like a belt.(2) the suspendedmatters in this turbid plume is predominantly consisted of inorganic particles from seabed, which grain size is usually less than60u m.(3) the forming of this belt liketurbid plume is more likely attribute to ihc restriction of suspension seaward dUl'usingin tidal cycles,(4) in the area outside the turbid plume, the SSC decrease sharply dueto weak hydrodynamic conditions and coarser sea bed sediment. Only the fineparticles in sea bed sediment can be resuspended, In some cases, the surfacescdimcnl on sand ridges is too coarse lo be resuspended and the suspend matters inwater column above these sand ridges are transported from adjacent channels byconvection.Four kinds of sedimentary faces have been ickruinol in the stratum of radialsand rid"ges area:"ridge top f"ace,"ridge slope face,"shallow water channel face*,and "deep water channel face"c. The transverse remotion of ridges dedue ansuccessively emerging of lour faces in stratum, which display a up-coarser trend oflithology. We also can find this kind of 'Yidge transverse ermotion sequence" in thestratum of mud patch between abandoned Yellow River estuary and radial sand ridges,which has been eroded on the top and covered by mud layer of several ten centimetcn;.The existence of eroded sand ridges sequence in stratum of mud patch indicate thearea of sand ridges may extend more northward before1855than present, whenYellow River still debounched into Yellow Sea and can supply enough coarsesediment for sand ridges.As a method of inferring net sediment transport pathway from spatial distributionof grain size parameters, the Grain Size Trends Analysis {GSTA) has been employedwidely in cases of marine geology studiesonce. In this paper, based on the cpt of''d"ynamic populations^a one dimension suspended sediment transport modal hasbeen established to deduce the formation of grain size trend in the net sedimenttransport directionod. The result show thai:if the hydrynamic energy level decreasingalong sediment transporting direction, two kinds of grain size trend can form successively in the transporting directionï¼› whereas, if the hydrodynamic energyincreasing along sediment transport direction, three kinds of grain size trend can formsuccessively at most. The speed of hydraulic dynamic energy enhancing/attenuationcan obviously change the GST distribution along transporting path, Higher speed canenable the GST transform complete in shorter distance. The value of kurtosis has thesame variation trend as Std and can be more sensitive to mixing ratio changing,theerfore, better ersult can be gained if we replace the Std with kutrosis in GSTA.