Reconstruction of Oligocene Lake Level Change through Onlap Points: A case from Liaozhong Depression,Bohai Bay Basin

Standard sequence involve HST,TST,FSST and LST.Through analyzing the features of onlap points in the systems of standard third-order sequences,the onlap points of a standard sequence can be divided into five kinds,which are onlap points of LST,onlap points of TST,onlap points of early HST,onlap points of late HST and onlap points of FSST;and bring forward the way of inverting lake level change history by counting onlap points in the sequence.Use this method,which can be used in conjunction with the features of stratigraphic section in Liaozhong depression,the Bohai Bay Basin;on the basis of dividing third-order sequences,count the onlap points and plot a coastal process curve and a lake level eustasy extent curve,and divide Oligocene into four lake level eustasy cycle,then,through contrasting the vertical variation of drilling sediment,we find that the lake level is highly confident curve,it also proves that the way of inverting lake level change by counting onlap points is practicable in the study of continental paleolimnology.