Sequence-stratigraphic dynamics: Variations of genetic stratigraphic units driven by basin subsidence

摘要

Rapid basin subsidence can cause the stacking of all strata deposited within a third-order eustatic cycle in a backstepping pattern. However, such extreme changes in stratal stacking patterns remain unexplored due to the lack of case studies. In this study, we first introduce the concept of sequence-stratigraphic dynamics based on previous achievements, and investigate the normal variations of genetic stratigraphic units of a third-order cycle driven by basin subsidence using mathematical simulations and a case study. We have established a dynamic equation and a system for the evaluation of the variations in genetic stratigraphic units based on which 6 potential driving mechanisms and 36 genetic unit variations, including 2 extreme variants of normal and reverse, were identified. The results confirm that third-order cyclic sea level change (Rsea-level), generalized basin subsidence (Rbase), and the sediment supply (Rsediment) drive the changes in the stratigraphic architecture. However, the variations of genetic stratigraphic unit are driven by the residual basin subsidence rate (Rbase - Rsediment). The stratal stacking pattern depends on the ratio of sediment supply rate to the residual accommodation rate (Rsea-level + Rbase - Rsediment). Sequence-stratigraphic dynamics are applicable to all basins, and may lend themselves as a theoretical basis for wider stratigraphic correlations.