Application of a dual‐lithology, depth‐dependent diffusion equation in stratigraphic simulation

A process‐based dynamic‐slope approach is incorporated in a two‐dimensional (2D) stratigraphic basin simulation software. It is based on the classical topographical diffusion concept, but in contrast to previous models it predicts down‐slope sorting of two grain‐size classes (here sand and mud). The effect of compaction is included in the mass balance, as well as arbitrary depth‐dependent transport coefficients (difrusivities). Each lithology will have its own transport‐coefficient function, which can be tuned to predict realistic lithology dispersion (e.g. trapping of sand in shallow‐marine environments). The set of partial‐differential equations is solved numerically by using a fully implicit finite difference method, applying a Newton iteration scheme on the non‐linear equations. Simulations show that the mass balance due to compactional effects is taken care of. A case from a technically quiescent margin demonstrates, as commonly observed in nature, that the sand fraction increases on the alluvial plain when accommodation space is limited. In the marine part, sand‐rich coarsening‐upward sequences form during progradation, while a condensed and partly erosional maximum flooding surface (MFS) forms during transgression. The MFS is associated with very shaly lithology, a feature that is observed both in field work and on geophysical well logs. If compaction and isostasy modelling are included in this case, the overall architecture is altered. The deposits become proximal, and the timing of maximum regression, etc. is modified. Alternatively, if the time span of simulation is doubled, the result is lower slope angles and increased penetration distance of the sediment wedge into the ljasin. Thus, it is demonstrated that a process‐based dynamic‐slope approach with lithology sorting is a rich alternative to more geometrically based models when the formation of large‐scale stratigraphic architecture is investigated.