Seismic onlap curves

which was called by P.R.Vail et al"the curves of relative changes of sea level"

have been used in correlating continental sequences.This extensive useage

however

sounds doubtful to us owing to the following facts:1.There are 3 kinds of continental basins according to their (water) interconnection with ccean.Water surface in two out of the three kinds

the drainage basins and interior basins

are controlled by the elevation of overflow and climatic conditions respectively.The border basins

i.e.

the sole kind that has water surface rising and falling synchroniously with sea levcl

can be considered as peripheral parts of sea basins

and not really continental ones.2.The onlap points of continental deposits might float within a very wide elevation range

thousand meters above

beneath

or about the lake surface.3.It is more difficultto distinguish normal(coast)onlap and abnormal ones(under-water and areal onlaps)in seismic sections of non-marine sequences than in marine sequences

and may cause lots of confusions.We suggest that onlap curves can not be taken as the curves of relative changes of lake level

not to mention their appliction in correlation of non-marine sequences.It is unreliable to use the similarity of seismic onlap curves to deduct the connectivity between onlap basins.