Salt canopies form the most spectacular and complex structures in the realm of salt tectonics. In this study, we use two physical models to examine salt-canopy growth and evolution on a salt -detached slope. A series of 14 feeders were seeded in our models and grew upward as passive diapirs. Eventually, these passive diapirs spread as salt sheets, with motion vectors skewed down the imposed regional dip slope. Sutures between individual sheets were bowed in the direction of override and became dis-membered as the canopy system matured. Feeders in the interior of the array faced increasing competition for salt due to draw -down and primary welding. In contrast, feeders on the canopy peripheries faced less competition and rose more vigorously, generating local elevation-head gradients and imparting salt -flow directions that were highly oblique to the regional dip slope. Finally, our model canopies were loaded by prograding sediments. Canopy formation is strongly controlled by the salt budget, among other factors, and our less mature model formed a series of small canopies and isolated salt sheets. During sedimentary loading, this model displayed intrasheet and intracanopy inflation-deflation flow cells as salt was driven downdip. Sutures were further dispersed, and some were everted. Loading of our mature model deflated the originally continuous canopy, driving salt seaward up a series of base-salt ramps to form a shallow distal canopy. Suture fragments were carried all the way to the toe of this shallow canopy.Our more mature model was also shortened before loading, which resulted in canopy remobilization, thickening, and enhanced suture deformation. Salt flow during shortening was channeled by feeders, forming salt streams with orientations commonly oblique

Minibasins are fundamental components of many salt-bearing sedimentary basins, where they may host large volumes of hydrocarbons. Although we understand the basic mechanics governing their subsidence, we know surprisingly little of how minibasins subside in three-dimensions over geological timescales, or what controls such variability. Such knowledge would improve our ability to constrain initial salt volumes in sedimentary basins, the timing of salt welding, and the distribution and likely charging histories of suprasalt hydrocarbon reservoirs. We use 3D seismic reflection data from the Precaspian Basin, onshore Kazakhstan to reveal the subsidence histories of 16, Upper Permian-to-Triassic, suprasalt minibasins. These minibasins subsided into a Lower-to-Middle Permian salt layer that contained numerous relatively strong, clastic-dominated minibasins encased during an earlier, latest Permian phase of diapirism; because of this, the salt varied in thickness. Suprasalt minibasins contain a stratigraphic record of symmetric (bowl-shaped units) and then asymmetric (wedge-shaped units) subsidence, with this change in style seemingly occurring at different times in different minibasins, and most likely prior to welding. We complement our observations from natural minibasins in the Precaspian Basin with results arising from new physical sandbox models; this allows us to explore the potential controls on minibasin subsidence patterns, before assessing which of these might be applicable to our natural example. We conclude that due to uncertainties in the original spatial relationships between encased and suprasalt minibasins, and the timing of changes in style of subsidence between individual minibasins, it is unclear why such complex temporal and spatial variations in subsidence occur in the Precaspian Basin. Regardless of what controls the observed variability, we argue that vertical changes in minibasin stratigraphic architecture may not record the initial (depositional) thickness of underlying salt or the timing of salt welding; this latter point is critical when attempting to constrain the timing of potential hydraulic communication between sub-salt source rocks and suprasalt reservoirs. Furthermore, temporal changes in minibasin subsidence style will likely control suprasalt reservoir distribution and trapping style.

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.

Lateral shortening is expressed in unique ways in salt basins, especially if pre-shortening diapirs are present. We present an overview of previously-published and new physical models and present new 3-D conceptual models that capture the evolution of shortening structures in salt provinces dominated by precursor isolated diapirs (termed isolated-diapir provinces). In such provinces, isolated diapirs form only a minor volumetric component of a sedimentary basin, however, due to the relative weakness of rock salt and their ability to localize strain, during shortening they have a disproportionately large influence on structural development. We find three key mechanical principles govern the processes and structural styles developed during shortening of isolated-diapir provinces. First, salt diapirs shorten before surrounding sedimentary rocks due to their relative weakness, and so form salients in the thrust front during early shortening. Second, diapirs tend to nucleate folds and faults, which radiate out from the diapirs. Third, as diapir walls converge, the roof must shorten. Extrusive salt sheets are expelled through thin roofs, but thicker roofs resist piercement and so tend to undergo complex folding and faulting. As a result of these principles, the first-order controls on the structural styles expressed across a shortened isolated-diapir province are the configuration the diapir array prior to shortening, the connectivity of these diapirs prior to shortening, total strain magnitude, and diapir roof thickness. Second-order controls include the initial cross-sectional and map-view geometry of diapirs, diapir size, and diapir orientation with respect to the shortening direction.

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Intrasalt sediment packages containing siliciclastic sediments, carbonate sediments, or non-halite evaporites such as gypsum or anhydrite are common within most salt sequences. Intrasalt sediment packages may have been deposited before, during, or after salt deposition and be incorporated into the salt by various processes. Understanding the origin and evolution of intrasalt sediment packages may yield important insights into the tectonic and geodynamic history of the basin, and also into the understanding of salt tectonics. Despite the importance of intrasalt sediment packages, currently there is no systematic description of their possible origins and their distinguishing criteria. This work is divided into three parts. The first part outlines the possible origins of intrasalt sediment packages, as well as criteria to determine if they originated as subsalt, suprasalt or intrasalt sequences. The second part examines how sediment packages that originated on top of salt, such as minibasins, can be encased within salt. Four key encasement processes are proposed: a) salt expulsion from beneath a minibasin experiencing density-driven subsidence; b) salt expulsion from beneath adjacent subsiding minibasins; c) salt expulsion associated with lateral shortening; d) override of minibasins by a salt sheet sourced from elsewhere. The third part of the paper presents a case study from the SE Precaspian Basin, Kazakhstan, where, using a borehole-constrained 3D seismic reflection dataset, the proposed criteria are applied to an area with abundant, newly discovered sediment packages within salt.

The SE Precaspian Basin is characterized by an assemblage of Upper Permian to Triassic minibasins. A recently acquired borehole-constrained 3D reflection dataset reveals the existence of abundant intrasalt reflection packages lying in between the Permo-Triassic minibasins. We propose that most of the mapped intrasalt reflection packages in the study area are minibasins originally deposited on top of salt that were later incorporated into salt by encasement processes. This makes the SE Precaspian Basin a new example of a salt province populated by encased minibasins, which until now had been mainly described from the Gulf of Mexico. Identifying salt-encased sediment packages in the study area has been crucial, not only because they provide a new exploration target, but also because they can play a key role on improving seismic imaging of adjacent or deeper stratigraphic sections.

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Salt tectonics is the study of how and why salt structures evolve and the three-dimensional forms that result. A fascinating branch of geology in itself, salt tectonics is also vitally important to the petroleum industry. Covering the entire scale from the microscopic to the continental, this textbook is an unrivalled consolidation of all topics related to salt tectonics: evaporite deposition and flow, salt structures, salt systems, and practical applications. Coverage of the principles of salt tectonics is supported by more than 600 color illustrations, including 200 seismic images captured by state-of-the-art geophysical techniques and tectonic models from the Applied Geodynamics Laboratory at the University of Texas, Austin. These combine to provide a cohesive and wide-ranging insight into this extremely visual subject. This is the definitive practical handbook for professional geologists and geophysicists in the petroleum industry, an invaluable textbook for graduate students, and a reference textbook for researchers in various geoscience fields.