A semi-quantitative method for the reconstruction of eustatic sea level history from seismic profiles and its application to the southern South China Sea

Abstract

A quantitative model is proposed to estimate the magnitude of eustatic sea level fluctuations on the basis of definitions of relative and eustatic sea level. In this model, factors such as erosion, sedimentation, compaction, basement tectonic and loading subsidence, and paleo-bathymetry are considered. To estimate incremental changes in eustatic sea level, we developed methods to solve for the variables involved in the model on the basis of interpretation of seismic profiles. We reconstructed the onlap/offlap points removed by erosion by fitting the effective thickness in areas without erosion with a piecewise-defined function and extrapolating this function to zero thickness. We used decompaction and backstripping algorithms to remove the effect of compaction and to calculate loading subsidence of the basement. Regional data, however, are needed to estimate the paleo-water depths and the tectonic subsidence. For this reason, our methodology is considered semi-qualitative. As an application of this model, an eustatic sea level curve since the Pliocene (5.33 my) was deduced from interpretation of our high-resolution seismic data from the northern Sunda Shelf, South China Sea (SCS). On this curve, 36 fourth order sea level cycles were recognized with periods ranging from 0.08 to 0.29 my. The curve matches well with the smoothed deep-sea stable oxygen isotope curves from benthic foraminifera.