Diachronous Growth of Fold Limbs from the Mad Dog Anticline: Implications for Base-Salt Deformation in the Atwater Fold Belt

Michael R. Hudec
Bureau of Economic Geology, The University of Texas at Austin, Austin, TX

Restoration of a cross section across the Mad Dog anticline, Green Canyon area, northern Gulf of Mexico, shows that the two limbs formed at different times by different processes. The southeast limb formed during late Miocene-Pliocene shortening of the Atwater foldbelt. However the northwest limb formed by salt withdrawal after shortening had ceased.

Most of the salt expelled from the deep salt layer beneath the northwest limb of the fold moved up into the Mad Dog salt sheet that lies over the top of the fold. This indicates that some feeders connecting the deep layer to the shallow salt sheet must have remained open after shortening stopped. The presence of one or more open feeders has important implications for mapping feeder-flank traps in the area.

Late salt expulsion deformed the base of the Mad Dog salt sheet in conformance with subsalt sediments. If late expulsion is widespread, it would have important implications for subsalt mapping in areas with poor subsalt seismic data. In particular, it suggests that base-salt structure may not be entirely a product of salt-sheet emplacement. Thus, lows in the base of salt mapped as salt-ascension zones may instead be synclinal folds.

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas