Analysis Of Sedimentary Environment Characteristics Of Boreholes In The Eastern Plain Of The Dayang River Area Of Eastern Liaoning

The Liaodong Peninsula is located on the east coast of the Eurasian continent and borders the Yellow Sea to the east.It is sensitive to the transgression and regression of climate change.As one of the main rivers in the peninsula,the sedimentary strata of its alluvial plain can well represent the changes of the sedimentary environment at that time.In this thesis,the neritic sediment（DYH borehole）since the early Upper Miholocene in the alluvial plain on the east bank of the Dayang River in the eastern Liaoning area was taken as the research object.（1）The DYH borehole is mainly composed of clay silt,silt and silty sand,the upper clay part is mainly silt,clay and clay silt,indicating that the hydrodynamic force is weak;the lower sand and gravel part is mainly sand and silt.Sand,indicating strong hydrodynamics.The upper clay part of the sediment frequency curve shows a significant unimodal shape,and the overall particle size is relatively fine,reflecting that the hydrodynamic force is weak at this stage and the depositional environment is relatively stable;the lower sand and gravel part is multimodal,with significant coarse kurtosis.The probability accumulation curve is in a three-segment form,with the jumping component as the main component.The sorting of the moving and suspended components is better than that of the jumping component.The hydrodynamic conditions of the core show a gradually weakening trend from bottom to top.The upper clay part of the particle size parameter showed narrow kurtosis,nearly symmetrical and positively skewed,and the lower part of the gravel layer had a sand content of 50%or more,showing broad kurtosis,multiple skewness,and poor overall sorting.The research core contains three endmember components.EM1 and EM2 are fine-grained components,representing the fine-grained substances carried by weak water flow deposition.The content is higher in the DYH 1～4 stage and distributed in the uniform suspension area;EM3 is the coarse-grained material.The granular component,which increased significantly in the DYH 5stage,was distributed in the mixed region of rolling and suspended matter,indicating this hydrodynamically strong alluvial deposition.（2）The main elements of the constant elements in the study of drilling are SiO₂and Al₂O₃,with an average content of 54.95%and 18.86%,respectively.The content of major elements increased and decreased in stages with the change of depth,which was in line with the general law of soil-forming process.The selected element index CIA also has a good correlation with the A-CN-K diagram,Sa,Saf,residual coefficient,ba,alkali withdrawal coefficient,Rb/Sr,and the weathering intensity from the bottom to the top of the core shows strong-weak-weak-strong-weak trend.The A-CN-K triangle diagram shows that the elements Ca and Na are leached to a certain extent in the section,the plagioclase is weathered and decomposed,and the montmorillonite is seriously leached,which is consistent with the overall change of CIA,and the entire core belongs to moderate weathering sedimentary environment.（3）Deciduous tree pollen and shrub and grass pollen were the main sporopollen combinations in this section,with an average content of 47.19%and 30.73%.The sporopollen assemblage zone reflects that the warm-humid sedimentary environment gradually changed to dry and cold,and the content of the freshwater species Bisporaceae began to increase significantly from the stage III（95～169cm）,indicating that the seawater retreated from the eastern plain of the Ocean River at this time,and the original transgressive area was The freshwater lacustrine environment is basically formed,and the sedimentary environment has changed significantly,which is presumed to be a global volatility regression.Based on the above indicators and research data,it is inferred that the DYH borehole was formed during the early Middle Holocene（8～2.5 ka B.P.of the Dagushan Formation）during the global high sea surface period of 7～6 ka B.P.In the fluctuating regression so far,the core has formed an obvious transition from the gravel layer to the clay layer,and the depositional environment has changed from warm and wet to dry and cold.