Comparison of Allochthonous Salt Deformation and Sub-Salt Structural Styles, Perdido and Mississippi Fan Foldbelts, Deepwater Gulf of Mexico

By

LIRO, LOUIS M.

Veritas DGC, Houston, TX

3-D prestack depth migration (PSDM) volumes over the deepwater blocks of the Gulf of Mexico allow for quantified evaluation of the styles and extent of allochthonous salt deformation, and its relation to underlying structural culminations. Data evaluated over the Walker Ridge, Keathley Canyon and Alaminos Canyon lease regions display distinct structural trends related both to the position and frequency of paleo source stocks for the allochthonous salt as well as regional fracture zones.

In the Walker Ridge/eastern Keathley Canyon region, allochthonous salt geometry is related to position of paleo source stocks. Allochthonous transport of individual salt “cells” is in the 20 - 50 km range; lateral amalgamation of these salt features gives the false impression of larger individual salt features and greater transport distances. Underlying structures are two-fold; generally symmetric folds of Mesozoic and Paleogene strata are related to the Mississippi Fan Foldbelt and generally decrease in relief (but not necessarily area of closure) to the western limit of Walker Ridge, at the Keathley Canyon Fracture Zone. Salt-withdrawal inversion structures are more numerous and commonly larger than the Mississippi Fan Foldbelt structures.

In the western Keathley Canyon/Alaminos Canyon region, similar allochthonous salt emplacement geometries exist, although identification of paleo source stocks is more problematic and top salt surfaces are more convoluted even though overburden thickness is similar to that observed to the east. Sub-salt structures are high-relief box folds; withdrawal-related features appear less numerous.