The south of Bodong sag is abundant in oil and gas resources, but its exploration lacks significant breakthrough, which might be due to unclear understanding of T20, the interface of neogene and paleogene strata. This paper determined and characterized the T20 sequence boundary applying regional control, single well analysis, classification and comparison, combined with seismic and logging data. The results show that the T20 sequence boundary should be raised to a set of weak amplitude wave group according to ancient biological, lithologic composition and stratigraphic contact relationship. The surface boundary was characterized by toplap, and located at the top of retrogradational parasequence set; meanwhile, ancient biological population and quantity were changed between the upper and lower strata. The surface characteristics were different from that of the other areas because of the difference in lithology and lithofacies between the upper and lower strata of the T20 sequence boundary.

paleontological characteristics  /  lithologic composition  /  parasequence set  /  Bodong sag