A systematic technique for sequential restoration of salt-related extensional structures incorporates Airy isostasy to quantify both the loading subsidence and the change in water depth during any time interval. The results are used to generate paleo-sea-floor templates for restoration and to reconstruct evolving salt and sediment geometries. Paleobathymetries calculated by the restoration technique are compatible with paleobathymetric environments derived from biofacies analysis of benthic foraminifers sampled in five wells along a reflection seismic profile from western Eugene Island, offshore Louisiana, northern Gulf of Mexico. Furthermore, both aggradation and progradation rates measured from the restorations are consistent with regional depositional patterns. The results demonstrate that the restoration method adequately determines paleobathymetry and sea-floor paleotopography. Restoration of multiple sections can provide a framework for the estimation of sediment transport and deposition geometries and facies development.

The frontal fold of the deep-water Mississippi Fan foldbelt is used to investigate the relationships between folding and faulting in detachment folds. Seismic coverage shows the entire three-dimensional geometry, from termination to termination, and the deformation history as recorded by asymmetric growth strata on fold limbs. The fold is a salt-cored detachment fold cut by reverse faults on both limbs. Its three-dimensional geometry is complex, consisting of four separate culminations, each associated with a distinct fault or fault segment. Consequently, profile geometries vary significantly, but unsystematically, along strike. Data analysis and structural restoration suggest a three-stage evolution during Mio-Pliocene shortening: (I)preexisting, en-echelon salt pillows served as buckling instabilities for the initiation of detachment folds that experienced relatively minor lateral propagation during growth and linkage; (2) an increase in shortening rate was accommodated by break-thrust folding; and (3) the faults became inactive upon a decrease in shortening rate, such that further fold amplification occurred by rotation and uplift of the backlimb. There is a direct correlation between fold and fault geometries, and abundant evidence indicates that the geometries of individual fold segments dictated fault geometries. (C) 1997 Elsevier Science Ltd.Rowan, M. G

The Perdido fold belt is a frontier petroleum exploration province located in deep waters of the northwestern Gulf of Mexico. The anticlines are northeast-southwest-trending, symmetrical to asymmetrical, with concentric folds usually bounded on both flanks by steep reverse faults. The folds are interpreted as detachment-folds cored by autochthonous Middle Jurassic Louann Salt, The fold belt overlies rifted transitional crust characterized by northeast-southwest- trending basement highs and northwest-southeast transverse structures that;controlled the original salt thickness and subsequent fold geometry. Upper Jurassic-Eocene strata were folded during the early Oligocene (36-30 Ma), with deformation possibly continuing into the earliest Miocene, Postkinematic sediments gradually buried the folds, with younger strata progressively onlapping the highest structures. Some folds were reactivated during the middle Miocene, and a late phase of broad uplift during the Pliocene-Pleistocene is attributed to loading of the Louann Salt by the advancing Sigsbee salt nappe. The Perdido fold belt marks the basinward margin of a complex, linked system of gravitational spreading above salt, Updig Paleogene sedimentary loading and associated extension were accommodated downdip primarily by salt canopy extrusion. The 5- 10% shortening and folding occurred only after canopy feeders were evacuated and closed off. Subsequent loading and deformation were concentrated at higher, allochthonous levels.