Numerical modelling of stratal architectures resulting from differential loading of a mobile substrate

Abstract

A numerical model is presented in which a viscous layer flows in response to differential loading by deltaic sedimentation. No density effects are considered; the mobile layer and overlying sediments deform solely in response to differential thicknesses of sedimentary overburden. Modelling results include the following key features: (1) sedimentary depocentres are asymmetric and spoon-shaped, with flat-lying shelf strata grading laterally into foreset slope strata at a prograding shelf-slope break; (2) the locus of deformation is controlled by the position of the shelf-slope break; and (3) a displaced bulge of mobile substrate migrates seaward faster than the shelf-slope break progrades. Using viscosities characteristic of natural salt (η = 1016 to 1019 Pa s), the sensitivity of the model to several parameters is examined. Increasing the mobile layer thickness increases the rate of substrate withdrawal in a manner similar to decreasing its viscosity. A shorter sediment transport distance results in steeper depositional slopes and faster substrate withdrawal. Comparison with a Miocene example from offshore Texas demonstrates that structures qualitatively attributed to differential loading can be successfully modelled using reasonable values for sediment supply, relative sea-level rise, and substrate thickness.