Seismic Structural Analysis of Deep-Water Perdido Foldbelt, Alaminos Canyon, Northwest Gulf of Mexico

Van S. Mount, John Suppe

The Perdido foldbelt is located at the base of the continental slope in the northwestern Gulf of Mexico. Seismic data in the Atwater Canyon region, southwest of the Sigsbee escarpment, indicate that the Perdido foldbelt is at least 80 km wide and consists of large (8 km wide) flat-topped anticlines involving predominantly the 6-km thick Jurassic through Paleogene deep Gulf stratigraphic section. Deformation of Holocene sediments indicates active compression. All 62 Perdido foldbelt lease blocks acquired in OCS Sale 112 (August 1987) are located in water deeper than 1.2 km (4,000 ft); seven are in record water depths over 3 km (10,000 ft).

Process-based structural concepts and interpretation techniques developed in overthrust belts have been applied to compressive structures observed in seismic data from the Perdido foldbelt. Fault-bend fold concepts are used to interpret fold shapes, which tightly constrain the fault geometry at depth. Interpreted fault geometry beneath the Perdido foldbelt consists primarily of long flats and short low-angle (< 25°) ramps. Three types of fault-related folds (fault-bend, fault-propagation, and box folds), as well as interference between structures, are imaged in the Perdido foldbelt.

Compressional deformation in a deep-water depositional environment has led to incorporation and preservation of syntectonic growth sediments into the structure of the foldbelt. Simultaneous sedimentation and growth of thrust-related anticlines produces distinctive fold shapes that are key to proper deep seismic interpretation. Time-transgressive angular disconformities are widespread in the Perdido foldbelt because of nondeposition over the uplifted parts of thrust-related folds.

Conventional exploration interpretations commonly show diverging high-angle reverse fault geometries in the imaged strata. Fault-related fold interpretations are superior because they balance, quantitatively predict deep structure not imaged in the seismic, provide information on the timing of deformation, and imply a unique kinematic model, which may be important for understanding oil migration.

AAPG Search and Discovery Article #91030©1988 AAPG Annual Convention, Houston, Texas, 20-23 March 1988.