A study on the relationship between biostratigraphy and sequence stratigraphy in several designated global boundary stratotypes shows that the best way may be to take the GSSP at a point coincident with the base of the first widespread Leading Group biozone above the first flooding surface (FFS) of the relevant third-order sequence.It is suggested that the first flooding surface of the sequence should be an important reference criterion for the selection of GSSP.As the base of the first widespread Leading Group biozone chosen for the definition of GSSP could not be lower than the first flooding surface of the referred sequence,the latter surface may be an important criterion for the recognition and correlation of the chronostratigraphic boundaries.