Explanation for Differences in Deepwater Salt Tectonics Between the North-Central and Northwestern Gulf of Mexico
Michael R. Hudec
Bureau of Economic Geology, The University of Texas at Austin, University Station, Box X, Austin, TX 78713
Salt geometries in the deepwater northern Gulf of Mexico change dramatically across the Brazos transfer fault, attributed to differences in basement structure. The area to the west of the Brazos transfer has a 3–4-km-high step at the limit of oceanic crust (LOC), a basement high beneath the upper slope (the East Breaks basement high), and a nearby zone of cratonic uplift (the Llano uplift/San Marcos arch). By contrast, areas to the east of the Brazos transfer feature a 0–2-km-high step at the LOC, no basement high beneath the upper slope, and a more distant zone of cratonic uplift. To the west of the Brazos transfer fault, seaward salt flow was limited by (a) the dam formed by the high-relief step at the LOC, and (b) limits to salt supply imposed by the East Breaks basement high. Cenozoic uplift of the nearby Llano uplift tilted the margin, forming the Perdido foldbelt at the downdip end of the deep salt layer. Rising folds of the Perdido foldbelt blocked seaward advance of the Sigsbee canopy, allowing salt in the canopy to thicken dramatically. On the east side of the Brazos transfer, salt advanced much further out onto oceanic crust because the LOC step was lower, and because the absence of an intrabasin high meant that much more salt was available to feed the advance. Cenozoic tilting of the margin was less severe and the uplift was further away, producing a broad and diffuse foldbelt. The absence of large-relief folds at the seaward end of the system allowed the Sigsbee canopy to flow seaward unimpeded.
AAPG Search and Discovery Article #90158©2012 GCAGS and GC-SEPM 6nd Annual Convention, Austin, Texas, 21-24 October 2012