--> Abstract: Superposed Deformation and Structural Control of Salt Breakout in Radially Expanding Canopies, by Tim P. Dooley, Martin P. Jackson, and Michael R. Hudec; #90078 (2008)

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Superposed Deformation and Structural Control of Salt Breakout in Radially Expanding Canopies

Tim P. Dooley, Martin P. Jackson, and Michael R. Hudec
Bureau of Economic Geology, Jackson School of Geosciences, The University of Texas at Austin, Austin, TX

The Sigsbee Escarpment in the northern Gulf of Mexico represents the 750-km-long leading edge of an advancing salt canopy. Seismic and bathymetric data show that it comprises several lobes fed by numerous salt diapirs below the salt canopy. We built physical models of lobate salt sheets that initially pinched out against a landward-inclined base-salt ramp. These lobes and their thin overburden roofs then expanded radially by gravity spreading, while being fed by pulsed salt supply. During expansion, salt sheets increased in radius and perimeter, creating a complex superposition of structures in their roofs in the following sequence. (1) Concentric extensional fabrics form near the diapiric feeder during initial spreading. (2) These extensional zones then shortened while surmounting the base-salt ramp. (3) After surmounting this ramp, the roof again extended as the salt lobe expanded over the abyssal plain. (4) The roof then shortened again wherever sedimentation hindered the salt sheet advance. (5) Radial grabens produced by perimeter expansion, were later reactivated as oblique-slip faults that allowed differential advance of salt lobes. These radial structures localized extrusive breakouts from the salt canopy. With slow sedimentation, small lobes of escaped salt expanded rapidly before joining to form auto-sutures between them. In contrast, rapid sedimentation buried and inhibited advance of the leading edge of the salt sheet. This created prominent frontal fold belts and inflated the salt sheet until it broke out again farther landward where the roof was thinner and higher. Repeated cycles of burial and breakout created buried salt wings.

 

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