Basement controls on the downdip transport direction and internal salt structures of the Campeche passive margin foldbelt, southeastern Gulf of Mexico

Abstract:

The Campeche salt province forms a passive margin foldbelt with an updip shelf and slope zone of normal faults and a downdip, deep-water zone of folds, thrusts and salt related structures of mid-Miocene to Recent age. We have integrated shipborne magnetic and 23,600 line-km of pre-stack depth migrated 2D seismic data tied to published wells in order to reconstruct the geometry and dip variations of the top of crystalline basement along which the passive margin foldbelt evolved. The grid of magnetic data constrained with seismic reflection lines allows an improved image of the subsalt top basement surface at a depth of 6-15 km that is more difficult to map from seismic reflection data alone. Crystalline basement is inferred to be deformed Paleozoic rocks that are known from outcrops and deep wells in both Yucatan and Mexico. The magnetic image reveals the 40-55-km-wide and 400-km long marginal rift that has been mapped on seismic reflection data along much of the northern Yucatan margin and localizes the thickest areas of Bajocian salt. The marginal rift sharply truncates northwest-trending Paleozoic orogenic trends which form a planar, northeast-tilted, salt-covered surface. Variations in the Campeche passive margin foldbelt focused along the low of the marginal rift includes: 1) a 200-km-wide, updip, extensional zone of listric normal faults detaching on salt; 2) a 150-km-wide translational zone of folds, thrusts, and canopy; and 3) a 350-km-wide, downdip, contractional zone of salt-cored folds, and break-thrusts. We illustrate how each differently sloped basement segment and resultant original salt thickness is associated with a unique association of salt related structures.