Study On The Paleogene System Formation Sequence Stratigraphy And Depositional System In Qinnan Depression Of Bohai Sea

Based on the theories of continental sequence stratigraphy and sedimentology,this paper examines the sequence stratigraphy,sedimentary system,lithofacies paleogeography and source-reservoir-cap assemblages of Paleogene in Qinnan depression by means of logging,seismic and otherdisciplines.On the basis of a single well and seismic sequence stratigraphy analysis,calibrated by drilling VSP,using wells and seismic,recognise seismic sequence interface,and using geochemical data,logging data,paleontological data,Fischer graphical method to compiled the study area Paleogene deposition of lake level change curve.Developed Qinnan Paleogene sequence stratigraphy program that in the upper 4^thmember of Shahejie Formation is divided into two second-order sequences,Dongying group will be divided into three third-order sequence,Shahejie Formation I.Sec is divided into a three third-order sequence,third member of Shahejie Formation is divided into two third-order sequence.According to the single-well drilling core observation and analysis of sedimentary system,combined seismic facies analysis,logging curve shape,establish the research area sedimentary facies and seismic facies identification,identifying the main sandy sedimentary system type.Qinnan depression Paleogene identified several sedimentary facies,such as alluvial fan,braided river delta,fan delta,lakes,carbonate platform.Among them,the main development in Shahejie are large fan delta,braided river delta,shallow-semi-deep lake sediments.Dongying group developed large braided river delta,shallow to semi-deep lake sediments,locally developed small fan delta.According to the principles of map compilation,the task and the purpose of the study,This paper makes Sequence-based lithofacies and paleogeography mapping of the Paleogene strata in the study area,by making use of system tracts as the basic mapping unit.And based on the “single factor analysis and comprehensive mappingmethod”,and considering the various factors such as structural components of rock,sedimentary structures,palaeontological features and characteristics of well logs which can reflect the sedimentary environment,this paper makes some sequence-based compilation diagrams on sedimentary facies of Paleogene in Qinnan depression.A detailed description of the different system tracts facies characteristics and evolution of ancient land division.Summed up the third sections of the Shahejie sequence characteristic is a short distance from the internal provenance basin sediments,deep lake-large semi-deep lake area,but only in the gentle shallow lake edge development;Shahejie group A,Sec.sequence with three sections of the Shahejie are same sedimentary characteristics,and further expand the basin area,mainly in the area sag semi-deep lake sediments,shallow lake at the edge of a gentle slope development;steep developed fan delta;gentle developed braided River Delta,the portion developed carbonate deposition.Member 3 of Dongying Formation also inherited the characteristics of the underlying layer of sedimentary sequence,deeper lake area expanded significantly;steep developmental fan delta,braided developmental gentle river delta and shallow lake sandy deposition.The sediment source of Second section Dongying sequence and places farther away from the main basin;sedimentary filling phenomenon obviously,depression and the periphery of raised areas developed large-scale multi-braided river delta,shallow sag area developed semi-deep lake sediments.