Calculation of denudation amount with Milankovitch cycle method: a case study in Biyang Sag

The denudation thickness of Paleogene—Neogene unconformity in the Biyang Sag has been calculated with the Milankovitch cycle method.The calculation process has been divided into 2 steps.1)Put the strata classification and logging curves of all formations as well as sections and sub-sections into "studies system of cyclostratigraphy"(version 1.0) so as to find the 0.405 Ma period.In this way,the maximum dominant cycle and the sedimentary time for available strata can be calculated.2)Transform the denudation time besides of the above-mentioned sedimentary time for available strata into erosion thickness according to the 0.405 Ma period.It has been concluded that in the center of the sag,only Liaozhuang Formation is denuded.In Anpeng area which locates in the southeast of the sag,the denudation thickness is less than 100m and increases gradually to the west,northwest and northern margin of the sag,and finally exceeds 650m around the missing boundary of Liaozhuang Formation.Hetaoyuan Formation is also denuded near to the sag boundary,mainly 4.1-666.5 m thick,and the total denudation thickness is over 1000m.The known Oil fields in the sag mainly locate in the area with denudation thickness larger than 200m.