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.
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