Accretionary-Wedge Shortening Ccaused by Advance of the Sigsbee Escarpment, Alaminos Canyon, Gulf of Mexico

Teunis Heyn¹, Martin Jackson², Michael R. Hudec², Bill H. Hart¹, Russell L. Propes¹, Micah D. Reasnor¹, Holly L. Harrison¹, Graham Vinson¹, and William D. Bunting^1
1BP America, Houston, TX
²Bureau of Economic Geology, University of Texas at Austin, Austin, TX

A salt canopy is moving southwest along the eastern margin of the Alaminos Canyon by thrusting sediments in front of the Sigsbee Escarpment. T Two orthogonal Perdido anticlines affect the style of thrusting. Fold 2 trends northeast, and a Baha cross-fold trends northwest. Thrusting began after Fold 2 stopped growing. Differences in the folds and stratigraphy resulted in two distinct zones of imbricate thrusting, both beginning at the Plio-Pleistocene boundary.

Zone 1 (SE) contains imbricated strata that were thin and near horizontal before shortening. This accretionary wedge is narrow and tapers steeply. The wedge rests on a planar, low-angle detachment and is no longer advancing. Shortening was extreme because salt pushed against thin strata that offered little resistance. Behind the wedge, a base-salt flat formed as a thrust during southwestward salt advance over the initial basal detachment of the wedge.

The imbricated section of Zone 2 (NW) was thick when shortening began. A detachment formed along a curved weak unit in the Baha cross-fold. This weak unit comprised Pliocene sediment ponded between the rising Baha dome and Fold 2. The accretionary wedge is wide and tapers gently. Shortening is less, and the detachment is deeper than in Zone 1. Minor buckling above thrusts continues today. Thrust styles in Zone 2 result from resistance supplied by a folded detachment and the greater thickness of the imbricated layer. Normal faults in the crest of Fold 2 coincide with the boundary between the two thrust zones. These crestal faults influenced thrusting by providing lateral ramps and plucked pieces in the accretionary wedge of zone 2.

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