Examples of Late Shortening of Minibasins and Salt in the Gulf of Mexico (SE Mississippi Canyon) and in ExperimentsDr. Bruno C. Vendeville
Senior Research Scientist
Bureau of Economic Geology
The southeastern Mississippi Canyon area of the northeastern Gulf of Mexico comprises subcircular minibasins bounded by a polygonal network of remnant Louann salt ridges. The ridges started growing during the Late Jurassic and eventually evolved into isolated passive diapirs. The base of most minibasins had grounded onto the base salt by the middle Miocene, with a few inverting to form turtle structures. Both minibasins and salt ridges/diapirs were then remobilized in a compressional regime during mid- to upper Miocene gravity spreading of the prograding clastic margin.
We used seismic
data and physical models to determine how the preexisting minibasins
and salt ridges affect the salt system's response to late contraction.
In models, early formation of minibasins and salt ridges was triggered
by differential overburden deposition. Late contraction was driven by
increasing the regional tilt or applying tectonic compression. Results
indicate that shortening is not accommodated by formation of a typical
fold-and-thrust belt. Instead, shortening preferentially deforms the
preexisting salt ridges and minibasin flanks and drives further diapirism
and lateral salt extrusion. Contractional structures associated with
this tectonic phase include symmetric or asymmetric rejuvenated diapirs,
squeezed diapirs whose pinched-out stems serve as reverse faults, and
detachment folds. Because the minibasins do not move in the exact same
direction or by the same amount and because they can undergo rotation
about a vertical axis, the relative movement between adjacent minibasins
varies significantly and is accommodated by a linked network of contractional,
strike-slip, and extensional structures formed above the salt ridges.