Extrapolating the Original Positions of Removed Onlap-Offlap Points Using a Piecewise-Constructed Model of Effective Stratal Thickness

The shift of onlap offlap points is a critical factor in sequence stratigraphic analysis and charting sea level curves. Onlap offlap points, however, are easily removed due to tectonic uplift, eustatic sea level fall, and so on. How to recover the original positions of removed onlap and offlap points has still been a pending problem. In this paper, we presented a piecewise constructed function model to depict the lateral changes of stratal thickness along a dip section. It is assumed that the thickness of a stratum decreases exponentially from its maximum towards basin margin, and thins linearly on areas adjacent to the onlap offlap points. Using this model, the positions of removed onlap and offlap points can be extrapolated by fitting the thickness data in non removal areas. This approach is used in the study of the Pliocene to Pleistocene strata on the northern Sunda Shelf, South China Sea, and the results are to our satisfaction.