The response of salt layers to extensional faulting inferred from growth stratal patterns: an HCA numerical approach

The complex interplay between normal faulting and gravity-driven salt migration, is widely recognised as a major factor controlling the architecture and evolution in many passive margin environments. The feedback relationships linking the two factors makes the unravelling of their specific contributions a very difficult task. Growth strata patterns provide a powerful tool to unravel the evolution of fault-fold geometry, even in such complex tectono-sedimentary environments. We used the Hybrid Cellular Automata (HCA) forward modelling algorithm to simulate the evolution of sedimentation through time in response to both extension and salt tectonics. The HCA algorithm is a numerical, hybrid methodology between the cellular automata (CA) and the finite element method (FEM) philosophies. It allows to simulate layered rock units by creating a mesh consisting of a very large number of semi-independent cells. Syntectonic sedimentation is achieved by properly adding new cell strata on top of the structure with the proper link to the existing mesh. The use of the HCA method in a forward modelling approach allowed us to recognise the individual contributions of salt doming and fault activity in the present day distribution of the sediment thickness along a sector of the southern Atlantic passive margin. In particular, modelling the internal architecture of offshore geosesmic sections, indicates the occurrence of two major extensional events that triggered distinct salt migration episodes.