The rise and fall of diapirs during thin-skinned extension revisited

Physical modelling and observations from seismic sections led to a conceptual model for the rise and fall of salt diapirs during thin-skinned extension, published by Vendeville and Jackson in 1992. Their conceptual model considers an initially tabular two-layer salt–overburden system that is deformed by thin-skinned extension during synkinematic sedimentation, and comprises the formation of turtle structure anticlines bound by passive diapirs and mock turtle anticlines above falling diapirs. The present paper revisits this conceptual model’s underlying mechanism by means of coupled continuum–discontinuum model studies in a ‘numerical sandbox’. The results obtained generally tend to support the conceptual model and show that, with a non-compacting overburden, only a buoyant viscous substratum and a significant amount of extension will lead to the formation of mock turtle anticlines. These numerical results are however at variance with the expectations of the conceptual model, in that salt-cored turtle structure anticlines are found frequently, a feature attributed to the tabular initial geometry of the turtle structure horsts. Analytical squeeze-flow models are used to clarify the mechanical genesis of salt-cored turtle structures and can explain why initially bowl-shaped basins are less prone to develop residual mounds of salt at their base than basins with a tabular geometry.