In the sub-Alpine chains of Haut Provence, SE France, a very well-exposed Mesozoic sequence showing rapid thickness and facies changes associated with Jurassic and Cretaceous extension on the margin of the Ligurian Tethys has been deformed by ‘Alpine’ compression which occurred from the Late Cretaceous to the Pliocene. Although the geology has been very well known for decades, aspects of the structure remain enigmatic and cannot be explained by either Mesozoic extension or Alpine shortening alone. We infer that some deformation resulted from salt tectonics. A completely overturned, highly condensed Jurassic section near Barles village resembles the elevated roof of a Triassic salt body in a deep-marine basin. This carapace became overturned as a flap in the Middle Jurassic when salt broke out at the seafloor and overran the inverted flap as an allochthonous extrusion, comparable to those in the deepwater Gulf of Mexico or Angola. Later, Alpine compression exploited the weakness of the salt sheet as the Digne Thrust moved over the inverted flap. Although the flap is in the footwall of the thrust, evidence of soft-sediment deformation and other anomalous structures within the flap suggest that it did not originate as an overturned footwall syncline.
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.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.