Analysis On The Characteristics Of Paleo-lake In Paleogene In Jiyang Depression

Jiyang Depression is one of largecontinental faulted-depression lake basins in eastern China.Lots of works have been performed in the depressionfrom the view of sedimentology and petroleum geology,but few studies have been carried out on water characteristics of paleolake and paleobiocoenosis.In this paper,the data of cores,logging andseismicwere used and the analysis methods ofpaleontology and geochemistry were combined with.Based on the division and contrast of Paleogene sequence stratigraphy in Jiyang depression,the paleoecology and water characteristics of paleolake were studied,and the sedimentary environment evolution process of Paleogene was analyzed.The results are concluded as follows:(1)The sequence boundaries wererecognized by using cores,logging and seismic data.The strata of lower third Member of Shahejie Formation to Dongying Formation were divided into six secondary sequences and their characteristics were described.The controlling factors were analyzed with the view of the climatic conditions,deposition rate and tectonic movement.(2)The evolution of biocoenosis and sedimentary environments of six sequences wererecoveredby using dominance diversity.The paleoclimate characteristics of the sequences were analyzed by using palynological and geochemical methods.According to the characteristics of ichnology,thePaleogenepaleo environment model of Jiyang depression is established.(3)The water characteristics of paleolake,such as paleosalinity,Eh,pH,water depth,temperature,wereanalyzed using elements geochemical data.(4)The environmental characteristics and evolution rules of paleolakesin different depressionsand sequences in Jiyang depression weresummarized.This study could provide theoretical foundation for the paleolake environments and sedimentology,and haspractical significance for theexploration of oil and gas in Jiyang depression.