3D stratigraphic modelling of the interaction of marine and land processes

In order to investigate the interaction of marine and land fluvio-deltaic processes we have developed a fast yet representative model with a coupled fluvio-deltaic drainage network module and a marine sedimentation module. The focus of the model is on sediment dynamics and stratification on geological timescales (1000 years and longer), therefore the routines represent only those processes relevant on geological time scales. The algorithms are implemented in the overall architecture of a 3D stratigraphic model, which allows us to evaluate the resulting stratigraphy. The fluvio-deltaic setup is based on subgrid parameterization and is capable of producing convergent and divergent channel networks. The channel network is assumed to be stable, yet avulsions are allowed to develop out of randomly instigated crevasses. Channel stability is modelled one dimensionally by calculating the flow and sediment transport at prospective avulsion nodes. Marine sedimentation and erosion is represented by, longshore currents, river jets and wave influence. Hypopycnal plumes and longshore currents are integrated in one potential flow routine, thus allowing rapid calculation. Wave generation and propagation is modelled independently. The wave-current interaction allows reworking of previously deposited sediments, and consequent resuspension. The sediment dispersal of the resuspended load is assumed to occur exclusively due to longshore currents, as the effective velocity vectors of the waves are mostly orientated crosshore. Previous modelling efforts have shown that, under fully time-invariant forcing changes in avulsion frequency are correlated with the number and length of distributary channels, which are in turn related to alternating phases of progradational and aggradational delta development. This fluctuation in sediment transport results in changes of sediment flux (i.e. storage-and-release events) to the marine basin and ultimately the morphology of the delta front and prodelta. Additionally marine processes such as waves and longshore currents influence the morphology of the delta. Wave reworking may remove nearshore deposits or block potential outflow routes, which will in turn influence the progradation of the delta and consequently the fluvio-deltaic channel network.