The Grain Size Of Surface Sediments And The Reflection Of Diatoms On Sedimentary Environment In Jinzhou Bay

In this paper,the diatom identification(87 sampling points)and grain size analysis(122 sampling points)were carried out on the surface sediments of Jinzhou Bay sea area in the Bohai Sea,and the distribution characteristics of the dominant species of diatoms and diatom distribution of the substrate sediment species in this study area were calculated and analysed to explore the sedimentary environment in this study area by combining sediment types,grain size parameters,frequency curves,probability accumulation curves and C-M diagrams.A total of 33 genera and 50 species of diatoms were identified in 87 surface sediment samples from the Jinzhou Bay area,and the dominance formula resulted in a total of six dominant diatom species,namely Coscinodisus spp.,Cyelotella striata,Paralla sulcata,Actinocyclus octonarius,Dictycha fibula Ehrenberg,Surirella fluminensis.The dominant diatom species are widely distributed throughout the study area,with some variation in the main distribution ranges of diatoms,with more freshwater benthic and marine cement intertidal indicator species in the eastern part of the inlet and more pelagic indicator species near the shore in the west,with the eastern and western parts of the study area The eastern and western parts of the study area are indicative of the intertidal and subtidal environments respectively.The grain size parameters,outer ocean indicator species,inner bay indicator species,marine cement intertidal indicator species,seawater sand intertidal indicator species and freshwater benthic species content of surface sediment samples from Jinzhou Bay were analyzed by clustering using SPSS 19.0,and the study area was divided into three sedimentation zones by the proximity of sampling points and the characteristics of different diatom species combinations,combined with frequency curves,probability accumulation curves,C-M diagrams The diatom assemblage in Group I sedimentation area was mainly Cyelotella striata-Coscinodisus spp.-Dictycha fibula Ehrenberg,with high content of marine cement intertidal indicator species.The sediment type of this sediment area is dominated by clayey chalk,with small grain size,poor sorting-poor sorting,rich diatom species,less hydrodynamic,more stable depositional environment,and the comprehensive influence of incoming rivers,currents,and tides,the airport artificial island is located near the shore,it disrupts the flow direction of seawater,the hydrodynamic environment changes,the sediment grain size is small,and poor sorting.Due to the obstruction of the movement path of seawater,the freshwater diatoms brought by the river are blocked between the coast and the airport artificial island and cannot spread outward,resulting in freshwater diatoms mainly located on the eastern side of the airport artificial island and distributed along the coast,forming a relatively static and stable intertidal environment.The diatom assemblage types in the Group II sedimentation area are Cyelotella striata-Coscinodisus spp.-Actinocyclus octonarius,Cyelotella striataCoscinodisus spp.-Dictycha fibula Ehrenberg and Coscinodisus spp.-Dictycha fibula Ehrenberg-Surirella fluminensis,the sediment type is sand and chalky sand,coarse sediment grains,moderate to good sorting,simple hydrodynamic conditions,high hydrodynamic intensity,and a large number of pelagic indicator species of diatoms with salinity above 26‰.The study area of this group is more oceanic,and this sedimentation area is a subtidal sedimentation environment with larger sediment grains and stronger hydrodynamics influenced by tidal currents and currents.The diatom assemblage in the sediment area of group III is dominated by Cyelotella striata-Coscinodisus spp.-Dictycha fibula Ehrenberg,and the diatom species are more diverse.The sediment area is located in the northern part of the study area,extending laterally to the east and west ends of the study area,and reaching the coastal area in the east,and the freshwater benthic species and marine cement intertidal species are indicative.In the west,it extends to the offshore sea and shows a certain marine sedimentary environment,and in the north,it is hindered by the tides and currents from the east and west ant islands,and the sedimentary area shows a subtidal sedimentary environment with smaller sediment grains and less hydrodynamic forces influenced by the tides,currents and islands.