Numerical modelling of reverse-density structures in soft non-Newtonian sediments

Abstract

Abstract A numerical code has been used to simulate the flow patterns in geological soft sediments that are driven by buoyancy forces resulting from reverse-density stratification. The aim was to provide a clearer understanding of the different roles of initiating conditions, inertia and rheological behaviour on the morphologies and timing of formation of natural features such as load casts and flame structures. Particular attention was paid to the cuspate form of rising intrusions that is commonly seen in nature but that has proved elusive in most earlier experiments. The numerical results demonstrate that large localised initiating perturbations and inertial influence during flow both tend to cause a decrease in the wavelength of the resulting flow pattern and can, under certain circumstances, serve to promote a cuspate morphology. The use of a relatively low viscosity Newtonian fluid as an approximation of the coarse-grained upper layer coupled with, critically, power-law behaviour in the underlying clayey layer was also found to promote a cuspate form in the rising intrusion.