Research On The Method Of Land And Sea Change In Liaohe Estuary In Recent Centuries

The Liaohe River Delta has experienced a large-scale retreat process in the past100 years.In order to investigate the feasibility of using the Electric Conductivity method?EC?to study the change of land and sea in Liaohe estuary area,8 drill holes were drilled in the Liaohe Delta plain,and the lithology,particle size analysis and pH testing and EC testing.Through the ²¹⁰Pb and ¹³⁷Cs dating,the deposition rate of the borehole was obtained by combining the previous studies.The relationship between EC and pH and clay content was discussed.The boundary between the land-continent phase and the continental phase in the Liaohe estuary area was proposed.According to the historical map,The effectiveness of the EC method in restoring land and sea changes has been obtained.The main understandings are as follows:?1?Dividing the land-sea transitional-continental phase with a specific EC value,lacking wide applicability.The EC division limit should be an interval value.In the Liaohe estuary area,the boundary between the sea-land transitional facies and the continental facies is 0.40⁰.70mS/cm.?2?EC and pH in the sedimentary environment of the marine-continental transition phase,R²=0.42⁰.82,there is a significant negative correlation;R² is low in the continental environment,and the correlation is not obvious.The sea-land transition phase environment with high EC value has a neutral to acidic pH.the closer to the modern coast,the stronger the negative correlation between EC and pH.?3?There was no significant correlation between EC and clay content in the marine-continental transitional facies and continental strata,indicating that EC has little to do with the clay content.?4?In the Liaohe estuary area,each hole experienced a sedimentary process of sea receding,indicating that the evolution process of the marine-continental transitional-continental phase is widespread in the Liaohe estuary plain.The average average deposition rate of LH24 pores is about 1.06 cm/a,and the age of EC is changed from sea-land transition to continental phase in about 1810.The borehole is located on the ocean side of the 1800-year-old coastline in the evolution map of the Liaohe estuary,which began to accept terrestrial sediments after 1800.The LH56 hole EC results are also confirmed by historical data,which verifies the accuracy of the ancient map.