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Salt Diapirism Generated by Shortening and Buckle Folding


Vendeville, Bruno C.1, Virginie Gaullier2 (1) Université de Lille 1, Villeneuve d’Ascq Cedex, France (2) Université de Perpignan, Perpignan, France


Seismic data from the Gulf of Lions show a series of large piercement diapirs at the downdip end of the system, in a region otherwise dominated by salt-cored folds. Can short­ening or buckle folding lead to the formation of piercement diapirs? Piercement to the sur­face requires that the average density of the overburden exceeds the density of salt. For clas­tic sediment, this requires a thickness of 3750 m, a computation that varies depending on which compaction curves are used. It is thus difficult to imagine early piercement to the sur­face through a clastic overburden. Could shortening provide an answer? In salt-cored buck­le folding, salt originally flows into the fold cores, and then is later forced back out as the fold tightens. However, if the synclines are grounded, there is no salt layer for the salt to flow back into. Continued tightening of the folds forces salt to rise up as it would in a diapir reju­venated by shortening. This can lead to piercement, even if the overburden is less dense than the salt. Grounding of synclines is favored in a simple shear scenario, where the over­burden is shortening more than the salt.