Deformation Styles of Allochthonous Salt Sheets during Differential Loading Conditions: Insights from Discrete Element Models

The growth history of allochthonous salt sheets and the subsequent deformation and formation of overlying roof geometries (e.g., roho and counterregional salt systems, and salt wall and minibasin formation) has been explored in the past using geometric restorations of seismic interpretations, as well as, physical and numerical models. However, there are still many fundamental questions about the physical and mechanical controls of these processes. Physical models produce realistic three dimensional (3-D) geometries but are difficult to probe for stress and strain field changes during deformation. The majority of numerical models have employed 2-D finite element methods that treat both the salt and its overlying sediments as viscous materials – precluding brittle deformation that must occur during deformation of the sediment layers.

In this study, I use the Discrete Element Method (DEM) to simulate the growth and evolution of allochthonous salt sheets in both 2-D and 3-D. My work attempts to answer the question of how different salt sheet geometries (e.g., length, thickness, preexisting basement structure) and loading conditions (e.g., sedimentation rates, slope angle, and horizontal loading) change the emergent salt structures and their accompanying roof deformation styles. Initial results show that low sedimentation rates, high basal slopes, and thicker salt sheets create weak roof configurations that result in greater downslope extension of both the salt and sediment layers. Extension is accommodated by listric roho type faults. Counterregional faults did not develop into counterregional salt systems due to the weak nature of the sediment particle configuration. Contact bonding has been introduced to strengthen the sediment layers and allow salt particles to exploit weakened fault zones for the formation of salt walls, diapirs, and canopies.