The analysis of sedimentary base level is the key to the identification and correlation of isochronostratigraphic units.The qualitative or semi quantitative baes level curves could be constructed based on the analyses of seismic data and well logs.(1)The onlap curve that represents baes level changes could be obtained by the correlation of differential subsidence

decompaction and stratigraphic restoration based on the identification of basin margin onlap

coastal onlap and marine onlap in seismic sections.(2)Milankovitch cycles could be identified through spectral technique of well logs;accommodation curve reflecting base level cycles could be established by means of corrected Fischer plot.Sedimentary base level curves obtained by different analysis techniques of seismic sections and well logs in North Tarim show good consistency

and they could be in the analyses of sequence stratigraphy

determination of sequence orders

correlation of interwell strata units and the study of tectonic and depositional histories of a basin.