Study On Northern Liaodong Bay Modern Deposition

The Bohai sea, composed of Liaodong bay, Bohai bay, Laizhou bay, the central basin and Bohai strait, the average depth of18m, through the Bohai Strait interchange sea water and energy with Yellow Sea. Since the last deglaciation periods, sea water re-cover the original land of Bohai deposition to form:a large underwater delta of the Yellow River, Luan River, Liaohe, the scale of Liaodong shoal tidal sand ridge along the Liaodong Bay15m depth shallow-scale mixed the discrete distribution tidal sand ridges monomer, NE-SW extension of the central basin argillaceous sediments District. Study area is20m water depth to shallow130km X100km the waters range of northern Liaodong Bay:northern part is Liaohe (China’s seven major rivers) and other river estuaries, developmental sizable intertidal and extends to about30m deep lines near the region’s the underwater river deltas; eastern and western along the coast to the harbor bedrock coast, the eastern coast of the underwater distribution of ancient coastal residue deposition area; Seabed terrain rendering of the study area from the coast to the bay central tilt trend, which both sides of the East and West tilt steeper; tidal range in the study area (maximum tidal range more than5m), a strong trend (2-3nmail), glacial length (the longest180days), land-ocean interaction strength is very strong. Predecessors have been carried out related research, but the historical investigation precision is not high, the survey is not comprehensive regional coverage, the small number of sample tests, sample test content is not comprehensive systems perspective concern emphasis on land and in the coastal zone, and more rarely detailed study of the impact of human activities on the offshore sedimentary and the suspension of the role and impact of modern sedimentary area of research. The paper comprehensively relying on "China’s coastal marine environment, a comprehensive survey and evaluation" CJ01the blocks Al investigations District1:50,000scale investigation of sediment, water, core sample data and Liaoning Province,"908Liaoning Province Coastal Zone Survey" tidal flat core sample data, the full range of particle size, detrital minerals, macroelement and microelement, the water (temperature, salinity and density), suspension (mass concentration and volume concentration),210Pb radioactive dating test analysis, to carry out a regional fine deposition distribution characteristics of modern sedimentary material sources, modern human activities affecting record suspension transport, the modern estuarine sediment dynamic process research, the basic conclusions of the following five major areas:(1) The average compositions of silt and sand are more than80%in regional sediments, mainly sandy silt and silty sand sediment types. The northwest nearly Xiaoling River estuary, between5-10m water depth, seabed sediments (silt) is finest, while seabed sediments (sand) in the southeast direction subaqueous sand ridge is the most coarse. Marine hydrodynamics, submarine geomorphological features and matter source are closely related to the distribution of seabed sediments. In addition to the southeast coast of sandy residue deposition is less affected by the modern material supply, the vast majority of marine sediment source is dependent on input of the rivers surrounding the gulf, especially the four rivers in the northern part.(2) In the seabed surface sediments, light minerals accounted for97.1%, and as major mineral, feldspar’s average content is59.8%, quartz29.3%. Highly unstable components of heavy mineral, mineral assemblage amphibole-epidote-garnet stone-tremolite, and K-feldspar and sphene are characteristic minerals in the region. The study area is distinguished from other Bohai areas with the high content of K-feldspar and hornblende.(3) In compositions of macroelement, the average SiO2and Al2O3content are up to67.47%and12.45%, followed by metal element content, TiO2, P2O5and MnO among the last three are less than0.58%. Element composition analysis shows that terrigenous coarse clastic and biological coarse clastic are the major factor controlling the distribution of elements. Heavy metals content relative higher, and distribution law in line with the granularity control law. Each measured metal remaining higher correlation with Al, reflecting the influence that the input material is near and terrigenous.(4)210Pb and137Cs dating reveals the northern intertidal deposition rate and deposition process. Tidal flat sedimentation is sensitive highly to the loads from river. Since the1980s, the deposition rate decreased significantly, and even some parts appear deposition and erosion interactions. The subaqueous delta deposition process is basically stable, and material supply and deposition rate of the test results reflect not show large fluctuations, remained at the level of2～6mm/a.(5) The suspension concentration distribution since estuary outward diffusion presents more obviously, and the underlying concentration is much higher than the surface. Tidal current and sea surface wind field increases the concentration of the suspension, especially in shallow water and the southeast coastal waters. Salinity28‰for the sector, the mass concentration of the suspension and turbidity showed varying degrees of linear relationship. Site volume concentration and mass concentration distribution are similar, flocs and biological components in seawater relative lower, the underlying suspension higher, and Liaohe diluted water front in the estuary obviously. In Liaohe undersea valley and Liaohe estury, site average particle size is coarse, about1-5Φ, the other area to5-7Φ.At an unprecedented density of stations, obtain research data uniform coverage throughout the northern Liaodong Bay, with full information, an adequate number of samples, credible analytical test methods, then the water, sediment and cores can reflect truly on the distribution and characteristics of suspensions, particle size, detrital minerals, geochemistry, deposition rate. By comprehensive in-depth study, there is a newer understanding in three aspects:(1) In the differentiation from the sediment distribution and power, refine and update the modern sedimentary characteristics of northern Liaodong Bay. Around the gulf circulation, in the central part of western study area, is typical clayey silt fine-grained sedimentary distribution area. Residual deposition area in eastern and western bay, and underwater valley remain coarse-grained sedimentary characteristics. The terrigenous detrital mineral power differentiation characteristics, and heavy metal enriched in the fine sediment are in line with the modern sedimentary characteristics.(2) River control weakened and influx control enhanced is notable features of sedimentary environment change in northern Liaodong Bay. Sudden drop in the amount of river water and sediment resulting decrease in material supply, and rivers in northern and eastern regions diluted water diffusion limit of suspended transport distance, the proliferation of detrital minerals diminished capacity to reduce the heavy mineral fractionation capacity, surface fine sediment again suspension handling reducing in situ deposition rate, and the original river affective deposition zone gradually trend by tidal deposits.(3) Human activity is an important factor of change and remodeling northern Liaodong Bay the modern deposition pattern and deposition. Severe reduction of river water and sediment input to build a reservoir sluice; reclamation activities to reshape the coast’s natural shape and spatial distribution pattern, limits the ability of shallow coastal waters during the modern sedimentary, indirect effects of the changes in deposition rate, detrital minerals dynamic fractionation and enrichment and diffusion of heavy metal elements.