APPLICATION OF DEPOSITIONAL BASE-LEVEL CONCEPT IN SEQUENCE STRATIGRAPHIC DIVISION, CORRELATION AND LITHO-STRATIGRAPHIC TRAPS PREDICTION

Depositional base-level cycle controls the development and evolution of sequence stratigraphy.Different from that in sea basin,the depositional base-level in continental basin is not sea-level or lake-level but river depositional equilibrium profile.During depositional base-level cycles,the sediment volume into different facies varies correspondence with its accommodation and that leads to the variation of sediment stacking patterns and symmetries of stratigraphic cycles.This provides scientific basis for sequence division and correlation.Correct chronostratigraphic correlation should be that of rocks to rocks,rocks to surfaces or surfaces to surfaces according to sediment volumetric partition.During depositional base-level cycles,the variation of accommodation controls the development of source rock,reservoir rock and cap rock in different system tracts and the forming of unconformity and various litho-pinch out. This is the basis of strata-lithologic traps prediction.In this paper,taking Songliao basin as an example,five principal types strata-lithologic traps and their particular formation conditions and distribution were analysed in the basin.