Flip-flop salt tectonics
This paper describes a common type of salt wall found in extensional regimes which possess the characteristics: cover strata truncated against both flanks; an asymmetric appearance in cross-section caused by normal fault-related growth patterns; and at least one unconformity and onlap surface separating strata which are tilted in opposite directions. This type of structure evolves by a process known as flip-flop salt tectonics starting with a roller where a normal fault detaches down one flank of the embryonic salt body. The structure grows as salt flows towards the low-stress zone below the crest of the footwall causing it to swell and tilt backwards until it becomes gravitationally unstable, until the cover strata on one or both sides welds out or until the salt emerges at surface. Further growth is then accommodated by switching to a new counter-dipping fault that detaches on the opposite flank of the salt body leading to a flip in hanging-wall/footwall polarity marked by an unconformity and onlap surface. The salt body continues to grow beneath the new footwall, causing partial inversion of the old hanging wall. Additional switches may occur, leading to tall flip-flop structures until the source of salt is depleted.