Abstract Salt is sensitive to the geometry of the substrate it flows across. We use physical models to investigate the impact of base-salt relief on deformation patterns. First, we investigate early-stage gravity gliding across base-salt relief. Salt flowing onto structural high blocks forms a zone of thickened salt and associated shortening owing to a flux mismatch. On the downdip edge of the basement high another flux mismatch generates a topographic monocline (ramp-syncline basin) with associated extensional and contractional hinges. With multiple base-salt high blocks, this structural pattern was repeated down the entire slope. Laterally discontinuous base-salt relief generated additional complexities such as major rotations of raft blocks and intervening diapirs as salt is channelled around and between base-salt relief. At the allochthonous level, regional dip, salt budget and base-salt relief influence flow patterns. Individual salt sheets spread sub-radially with streamlines skewed down the regional slope. As the canopy coalesced along allosutures, inward flow from the canopy peripheries dominated, driven by more vigorous flow from outer feeders owing to less competition for source-layer salt. Subsequent shortening returned flow patterns to grossly dip-parallel. However, salt flows fastest where it is thickest and thus chains of feeders channel rapid intracanopy flow.

Abstract Compared with the northern Gulf of Mexico, little has been published on the tectonics of its southern equivalent in the Bay of Campeche, especially in English. A middle Miocene change in the Pacific plate kinematics created the southern Mexico Neogene belt. This is locally expressed as four main fold belts underlying most of the study area: the Agua Dulce, Marbella, Marbella Norte, and Catemaco fold belts. Each fold belt contains productive Upper Jurassic and Cretaceous sections and may be part of a much larger fold belt that merges with adjoining fold belts in the Chiapas and Campeche areas. During the final stages of folding, salt was squeezed from diapirs and extruded over the eroded and uplifted fold belts. The extruded salt coalesced to form the discontinuous Sal Somera canopy. The salt canopy or equivalent weld is roughly conformable with the underlying fold belts, indicating that the canopy extruded during the final stage of folding or soon after. Evacuation of the thickest parts of the salt canopy allowed the greatest Pliocene–Pleistocene subsidence and minibasin growth. Three counterregional minibasins formed by seaward evacuation of the underlying salt canopy in the Pliocene–Pleistocene. Counterregional systems dominate the study area, the largest of which forms the seaward boundary of the 100-km-long (62-mi-long) Pescadores minibasin. Some minibasins are floored by the allochthonous salt canopy or equivalent salt weld, others rest directly on the fold belts, and others are more deeply rooted.

Abstract The Santa Ana area in the Bay of Campeche features a complex Neogene interaction of sedimentation, salt-related deformation, and regional tectonics. We synthesized this interaction using three-dimensional seismic data and logs and paleontological data from six wells. These provide a tectonostratigraphic framework for seven Neogene sequence-stratigraphic boundaries between 12.5 and 1.4 Ma. We analyzed these data using seven isochore maps, two restored cross sections, and a geohistory plot. The Neogene history begins with the Agua Dulce fold belt, which formed between 8.0 and 6 Ma. As the Agua Dulce folding waned, at about 6 Ma, extrusive salt blanketed much of the late Miocene fold belt. Sediment loading began to redistribute this allochthonous salt immediately after the discontinuous canopy was emplaced. Thin overburden sags may have originated as synclines during the waning stages of regional buckling, which also gently deformed the base of the salt canopy. After 3.8 Ma, the mean sedimentation rate more than doubled to 0.7 mm/yr (0.03 in./yr) as sediments became trapped against extensional, mostly counterregional, faults. Between 2.6 and 2.4 Ma, mean aggradation rates increased as much as sixfold to 4 mm/yr (0.16 in./yr) as major extension continued. A north block remained partly starved of sediment whereas depocenters formed proximally because of underlying salt evacuation. After 2.4 Ma, mean aggradation rates fell to 1 mm/yr (0.04 in./yr), probably because the shelf break crossed the study area. The boundary between thick distal sediment and thin proximal sediment shifted northward as the shelf edge prograded. Some depocenters merged in depressions in counterregional hanging walls. After 1.4 Ma, the north and west blocks acted as one, tilting seaward and accommodating the thickest strata.

Abstract Successful hydrocarbon exploration has produced a surge of interest in salt basins in the last 15 years. This attention, combined with advances in seismic data acquisition and processing, has revolutionized our understanding of salt tectonics. However, the wealth of information is also a glut. Conventional mechanisms for spreading knowledge through the geological community, such as papers and presentations, are woefully inadequate for handling the volume of information that now exists. It is difficult for interpreters newly assigned to salt basins to learn what they need to know, or for experienced salt interpreters to keep up with advances in the field. One solution to this problem is to try to merge the current understanding of salt tectonics with modern information technology. We are constructing a digital atlas of salt tectonics called The Salt Mine. The Salt Mine is an HTML-based, interactive atlas of salt structures and associated sediment geometries. When complete, the atlas will contain hundreds of images of salt structures from around the world, together with captions that discuss the processes illustrated. All images are grouped into structural styles, based on a geometric classification rather than on their mode of origin, which is often contentious. Images include field exposures (outcrop views, geologic maps, aerial photographs, and satellite images), seismic sections, geologic cross sections, conceptual sketches, and animations. In addition, the atlas will showcase hundreds of the best examples from the Applied Geodynamics Laboratory’s collection of physical and numerical models. Images in The Salt Mine can be located using five different methods: keyword search, geographic location, structural style, geometric classification tree, and a table of contents. In addition, three forms of help are available: list of references, glossary of salt tectonics, and a user’s guide. The goals of this effort are to provide novices in salt tectonics with a comprehensive guide that assumes no previous knowledge and to offer more-experienced workers a ready source of analogs and alternative interpretations.

Abstract The 500-km-long Sigsbee Escarpment overlies the leading edge of a salt-canopy system in the northern Gulf of Mexico. The escarpment separates the lower slope from the abyssal plain. Bathymetric relief of the escarpment ranges from 300 to 900 m, suggesting that the canopy is still advancing although it is almost everywhere buried beneath a roof comprising hundreds of meters of Pliocene–Holocene-age sediments. Existence of such a roof means that the canopy cannot be advancing by extrusion. Interpretations of the Sigsbee salt canopy have previously drawn attention to thrusts that root into the leading edge of the salt. These thrusts are inferred to accommodate intrusive advance of the salt allochthon over the abyssal plain. Based on our interpretation of 3D pre stack depth-migrated seismic data over a 48-km segment of the Sigsbee Escarpment, we propose accretionary advance as an additional hypothesis for salt sheet intrusion. In most of the study area, Pleistocene abyssal-plain sediments form an internally thrusted accretionary wedge in front of, and below, the leading edge of the salt canopy. As the salt and its siliciclastic roof advance, new thrusts break progressively farther out into the undeformed abyssal plain, increasing the cross-sectional area of the wedge. Because the footwall wedge contains synkinematic sediments, shortening decreases upward, so the upper reflectors of the accretionary wedge are more continuous than the lower ones. Stacking of imbricate thrusts backfolds the base of the salt sheet. By this means, salt flats can become distorted to form apparent salt ramps. The Sigsbee accretionary wedge has features in common with convergent-margin accretionary wedges, which are roughly ten times wider and advance faster. Potential geohazards are posed by the existence of currently shortening, or formerly shortened, accretionary wedges overridden by advancing salt sheets.

Abstract Deep-water structures in southern Gabon are among the best imaged in the world. Our 30-km-long study area in the Anton Marin–Astrid Marin blocks runs obliquely through the northern part of the Congo Fan. The study area is entirely covered by high-quality 3D seismic data. It spans the complex transition between the landward extensional domain and the basinward contractional domain. Both domains detach on Aptian salt. We use seismic sections and dip-corrected isochron maps to illustrate and analyze the following processes. Control of thrust location by precursor anticlines and diapirs: a regular wavelength of the early Albian gentle precursor anticlines nucleated linear, regularly spaced thrust faults; the location of precursor passive diapirs caused some thrust faults to curve to intersect with the diapirs, linking them into the overall contractional network, which includes lateral transfer zones. Thrusting that verged consistently seaward: most other salt-based thrust belts have less systematic vergence; we attribute the consistent vergence to the high frictional resistance of the salt detachment because it had been thinned by expulsion of salt into diapirs before thrusting began. Landward propagation of thrusting : during the late Cretaceous and Paleogene, thrusting propagated updip through the formerly translational domain because of the buttressing effect of older thrusts downdip of the study area. In the study area, distal thrusts and diapirs were still shortening while more proximal thrusts began shortening. Extrusion of salt sheets under compression: as thrusting culminated, the precursor passive diapirs were compressed to extrude salt; extrusion continued until the diapirs were finally squeezed shut, more or less coevally across the thrust belt in the study area.