Structural Evolution of the Mensa Minibasin, Mississippi Canyon, Northern Deep Gulf of Mexico

Aaron van den Berg, Renaud Bouroullec, and Paul Weimer
University of Colorado. Boulder, CO

The Mensa deep minibasin, in south central Mississippi Canyon, Gulf of Mexico, consists of several structural features that affected its geologic evolution. These are basement; autochthonous and three allochthonous salt deposits of upper Albian, upper Cretaceous and Neogene age; strike-slip faults; and a major “turtle structure” with extensive crestal normal faults. Remnant salt pillows are present throughout the minibasin atop both Albian and Cretaceous allochthonous salt deposits. These salt deposits formed weld surfaces beneath the Mensa gas field.

Analysis of 378 square miles 3-dimensional seismic data, together with wireline logs, and biostratigraphic information, indicates that the structural features evolved during several discrete intervals. From 99 to 24 Ma, an extensive allochthonous salt canopy existed as a bathymetric high that caused a condensed section to develop. From 24 to 15.3 Ma allochthonous salt deposits, of upper Albian and upper Cretaceous age, deformed into six remnant salt pillows. Early evacuation initiated diapirism that created modern salt nappes. Northwest-southeast paleocontemporary strike-slip faulting exerted structural control over the areal extent of Neogene salt canopies and the center of minibasin sedimentation.

From 15.3 to 14.35 Ma, multidirectional evacuation of salt ceased from beneath the Mensa gas field. From 14.35 to 9 Ma, salt evacuated around the flanks of these earlier thick deposits. A result was bowl and trough-shaped, external stratigraphic forms of a turtle structure. This period of salt evacuation permitted wedge-shaped external strata to develop and to onlap the turtle structures to the north and south of the basin.

AAPG Search and Discovery Article #90032©2004 GCAGS 54th Annual Convention, San Antonio, Texas, October 10-12, 2004