Geologic carbon storage (GCS) is a fundamental pillar of carbon management that helps mitigate greenhouse gas emissions and addresses the negative effects of climate change. Viable CO2 storage sites share some of the same elements required for successful petroleum systems. For example, while reservoir, seal, and trap are required, migration pathway and timing are not important for CO2 storage, because rather than withdrawing fluid from a trap, CO2 storage involves injection into a geologic trap. Conceptually, this represents a form of reverse production. Numerous petroleum traps around the world, as well as naturally occurring CO2-producing fields and natural gas storage sites attest that safe, long-term storage is possible. Research over the past two decades identified five methods of Geologic Carbon Storage which have been validated through several demonstration and pilot projects around the world: (1) storage in depleted oil and gas fields, (2) use of CO2 in enhanced hydrocarbons recovery (3) storage in saline formations/aquifers, (4) injection into deep unmineable coal seams, and (5) in-situ/ex-situ carbon mineralization. The greatest volumetric potential for GCS is found in saline aquifers which are present throughout the world’s sedimentary basins.

Hydrostatic or “normal” pressure can be easily visualized as a water column with pressure given by ρgh and any departures classified as abnormal pressure. This is the basis for commonly used hydrostatic pressure depth trends in sedimentary basins that are constructed on assumptions of constant gradients and are datumed at mean sea level or ground level. But the straightforward water column concept does not upscale in a simple way to sedimentary basins where the zones of interest are several thousands of metres below the land or sea surface. Sedimentary basins are heterogeneous, including stacked, confined reservoirs and variations in pore water composition. It is possible to construct pressure‐depth profiles that honour the geology and hydrostratigraphy of a basin and these give different hydrostatic baselines from simple constant gradients hung from familiar local datums such as ground level. Key steps are using a reservoir‐specific datums such as the water table or potentiometric surface relevant to that unit, then building a pressure‐depth trend that represents the pore fluid salinity variation and density profile throughout the reservoir unit. At a given depth, this version of hydrostatic may predict pressures several hundred psi different from a single density gradient hung from a datum local to the well, and exhibit a notched profile reflecting the geological and hydrological stratigraphy. This construct redefines normal and abnormal pore fluid pressures in sedimentary basins. The impacts of this alternative approach to sedimentary basin hydrostatics, even if data are limited and pressure profiles have to be framed probabilistically, extend to many aspects of studying and interacting with fluid systems in sedimentary basins including basin modelling, petroleum systems analysis, well planning and well operations.

Two-dimensional, plane-strain finite element numerical models produce small normal faults similar to those formed during the Oligocene to Miocene of the salt-cored St. Malo anticline in the deepwater Gulf of Mexico. The mechanical stratigraphy used in the models was derived from well data and a rate-independent, elastic-plastic constitutive model with a non-associated flow rule was used to represent the behavior of weak, over-consolidated rocks. Motion of salt is modeled by displacing the base of the overburden from an initially flat configuration to the observed present-day geometry. Model results using dominantly vertical displacement with minor extension (2%) are consistent with observed faulting at St. Malo. Small amounts of contraction (2-5%) in the numerical model suppress normal faulting whereas 2% extension best reproduces the observed structural style. The normal faults develop during elastic-plastic bending and evolve from sub-vertical, plastic mode-I failure zones to dominantly inclined normal faults. Throws of normal faults produced by the numerical models range from 11 m to 123 m. By comparison, the throws observed in the crest of the St. Malo anticline range from 30 m to 300 m. Models only using vertical displacement develop normal faults with >= 50 m throws due to bending; these are below seismic resolution. Only models with >= 2% extension develop normal faults that would be detectible (i.e., throws >= 50 m). A constraint of all the models is that the top of the salt is not faulted. The maximum depth of normal faulting in the models is ca. 900 m below the top of the reservoir. The maximum throws at the top of the reservoir in the models are ca. 30-65 m. Initiation of the normal faults as plastic mode-I failure zones in the numerical models suggests a mechanism that could facilitate early seal breach, even without juxtaposition of stratal leak points.

We report quantitative results from three brittle thrust wedge experiments, comparing numerical results directly with each other and with corresponding analogue results. We first test whether the participating codes reproduce predictions from analytical critical taper theory. Eleven codes pass the stable wedge test, showing negligible internal deformation and maintaining the initial surface slope upon horizontal translation over a frictional interface. Eight codes participated in the unstable wedge test that examines the evolution of a wedge by thrust formation from a subcritical state to the critical taper geometry. The critical taper is recovered, but the models show two deformation modes characterised by either mainly forward dipping thrusts or a series of thrust pop-ups. We speculate that the two modes are caused by differences in effective basal boundary friction related to different algorithms for modelling boundary friction. The third experiment examines stacking of forward thrusts that are translated upward along a backward thrust. The results of the seven codes that run this experiment show variability in deformation style, number of thrusts, thrust dip angles and surface slope. Overall, our experiments show that numerical models run with different numerical techniques can successfully simulate laboratory brittle thrust wedge models at the cm-scale. In more detail, however, we find that it is challenging to reproduce sandbox-type setups numerically, because of frictional boundary conditions and velocity discontinuities. We recommend that future numerical-analogue comparisons use simple boundary conditions and that the numerical Earth Science community defines a plasticity test to resolve the variability in model shear zones.

Reconstructing continental paleocrustal thickness is important for estimating tectonic accommodation, constraining three‐dimensional basin geometry during early rifting phases of extensional margins and predicting the distribution of thick crustal sills that may block the global ocean and create restricted basins. We test an inverse kinematic method for modeling paleocrustal thickness by inverting the final bulk crustal structure produced from high‐resolution thermo‐mechanical models of lithospheric extension. The inverse kinematic method assumes pure shear, includes simple rules based on geodynamic models and field observations and requires displacement boundary conditions and the prescription of a transition from rigid to nonrigid deformation. The inverse pure‐shear method produces a history of bulk crustal thickness that closely matches the forward models provided that the width of the rift zone is narrow during the later phases of continental extension when crust undergoes hyper‐extension. We also observe that the width and surface trace of large‐scale (LS) shear zones observed in the thermo‐mechanical models coincide with inflection points and large gradients in inverted nonrigid velocity field. Our results demonstrate that if displacement boundary conditions can be constrained and the transition from rigid to nonrigid deformation defines a narrow rift zone during hyper‐extension then relatively simple kinematic rules can be used to invert present‐day bulk crustal structure for paleocrustal thickness, bulk lateral strain and aspects of upper crustal shear zone geometry from extensional systems with nonlinear rheology, structures dominated by simple shear in the upper crust, depth‐dependent extension and asymmetric crustal thinning.

Two-dimensional plane-strain numerical experiments illustrate the effects of variable evaporite viscosity and embedded frictional-plastic sediment layers on the style of salt flow and associated deformation of the sedimentary overburden. Evaporite viscosity exerts a first-order control on the salt flow rate and the style of overburden deformation. Nearly complete evacuation of low-viscosity salt occurs beneath expulsion basins, whereas significant salt is trapped when viscosity is high. Embedded frictional-plastic sediment layers with yield strength partition salt flow and develop transient contractional structures (folds, thrust faults and folded faults) in a seaward salt-squeeze flow regime. Multiple internal sediment layers reduce the seaward salt flow during sediment aggradation, leaving more salt behind to be remobilized during subsequent progradation. This produces more seaward extensive allochthonous salt sheets. If there is a density difference between the embedded layers and the surrounding salt, then the embedded layers fractionate during deformation and either float to the surface or sink to the bottom, creating a thick zone of pure halite. Such a process of 'buoyancy fractionation' may partially explain the apparent paradox of layered salt in autochthonous salt basins and pure halite in allochthonous salt sheets.

Finite element modeling of contractional fault-related folding with critical state mechanics concepts reveals fundamentally different behaviors at two levels, depending on (1) mechanical stratigraphy and (2) initial fault geometry. Deviatoric plastic strain rate and strain patterns show that ‘strong’ layers, like normally consolidated sandstone or overconsolidated shale, develop strain localization in form of narrow plastic shear bands. ‘Soft’ layers like normally consolidated shale fail to develop localizations and respond by diffuse, distributed plastic strain. Inter-layered overburdens display both deformation modes. Models with listric thrust fault seeds develop basement-cored anticlines in the hangingwall that are characterized by locally tensile stress regimes within overall compressive regional stress fields. The anticline crests of these models show evidence for strain softening. By contrast, anticlines emerging in detached fault-related fold models are subject to locally compressive stress regimes, consistent with the applied far-field shortening. These anticline crests strain-harden during deformation. Stresses resulting from the finite element models deviate from stress estimates based on integrated densities. The discrepancy is small for basement-involved models but significant for detached style models, suggesting that stress predictions based on integrated densities may be inaccurate for contractional systems. First-order predictions of plastic deformation suggest that footwall synclines in basement-involved fold styles may host reservoirs with relatively poor quality owing to horizontal and vertical compaction. Anticlines found in detached deformation styles are bounded by compactive domains whereas the crestal regions are less affected by volumetric plastic deformation thus producing relatively better reservoir quality.

The phenomenon of rocks moving under their own means has always fascinated both scientists and nonscientists alike. The 2006 AAPG Hedberg Conference on Mobile Shale Basins was held in response to a need to gather industry and academic communities in a common forum to address the very existence of mobile shales. Stimulating and informative discussions at that Conference led to this special volume on shale tectonics. AAPG Memoir 93 documents shale tectonics from a variety of basins around the world, including the southern Beaufort Sea; the Krishna-Godavari Basin, India; eastern offshore Trinidad; offshore Brunei; and along the westernmost portion of the Mediterranean Sea. The book also provides information on the petrographic framework, behavior, geometries, and geodynamic models of shales. Publication of this Memoir coincides with a growing interest in shales as hydrocarbon reservoirs, and will add to the body of literature that significantly addresses both extrusive and intrusive shales.

Having established the first-order controls of the three primary salt tectonic structural styles of the Scotian Basin in paper 1, in this paper (paper 2) we investigate and show that many unexplained structures can be attributed to more complex initial geometries of the autochthonous salt basins than the simple rectangular shapes used in paper 1. Basement highs modify and reduce the efficiency of salt evacuation during sediment aggradation followed by progradation. Low-angle taper (similar to 3 degrees) of the basin edge slows Poiseuille flow and allows for trapping of salt beneath distal salt sheets. Seaward basement step ups do not necessarily hinder salt flow, and basement step downs can localize diapirs. Midbasin salt sheets can emerge when basement blocks as high as the salt is thick divide a basin into two subbasins. Deep salt basins that form above basement lows are efficiently evacuated. Weak overburden sediments augment the formation of salt sheets. Citation: Albertz, M., and C. Beaumont (2010), An investigation of salt tectonic structural styles in the Scotian Basin, offshore Atlantic Canada: 2. Comparison of observations with geometrically complex numerical models, Tectonics, 29, TC4018, doi:10.1029/2009TC002540.

Three primary salt tectonic structural styles of the Scotian Basin are compared with plane strain finite element models in order to investigate their origin. Here, we focus on simplified model salt basins with initial rectangular cross-sectional geometries and follow their evolution in the context of tectonic and parametric thermal subsidence and under various sedimentation regimes. Structural style A, an open-ended roho system with a synkinematic wedge, is reproduced by models including deltaic progradation and seaward spreading/gliding of sediments above a salt detachment. Structural style B, a linked salt tectonic system with landward regional normal faults and allochthonous salt sheets climbing seaward over Late Cretaceous and Paleogene strata, is shown to be a consequence of early aggradation followed by progradation. Structural style C is characterized by salt diapirs and intervening minibasins and is reproduced by models with Rayleigh-Taylor instabilities requiring compaction driven density inversions, weak sediments, and initial perturbations of the overburden-salt interface. Citation: Albertz, M., C. Beaumont, J. W. Shimeld, S. J. Ings, and S. Gradmann (2010), An investigation of salt tectonic structural styles in the Scotian Basin, offshore Atlantic Canada: 1. Comparison of observations with geometrically simple numerical models, Tectonics, 29, TC4017, doi:10.1029/2009TC002539.

The Perdido Fold Belt (PFB) is a prominent salt-cored deep water structure in the northwestern Gulf of Mexico. It is characterized by symmetric, kink-banded folds of a similar to 4.5 km thick prekinematic layer and its vicinity to the extensive Sigsbee Salt Canopy. We use 2-D finite element numerical models to study the evolution of the PFB as a gravity-driven fold belt both in a local context and in the context of the larger-scale passive margin, influenced by adjacent allochthonous salt structures. We show that parameters such as overburden strength, salt geometry, or salt viscosity determine timing, extent, and location of the modeled fold belt. Simplified models of the Gulf of Mexico show that toe-of-slope folding is a viable mechanism to develop diapirs in the deep salt basin and to delay folding of the distal overburden. In this scenario, the PFB likely represents the terminal folding of a much larger, diachronously formed fold belt system. Citation: Gradmann, S., C. Beaumont, and M. Albertz (2009), Factors controlling the evolution of the Perdido Fold Belt, northwestern Gulf of Mexico, determined from numerical models, Tectonics, 28, TC2002, doi:10.1029/2008TC002326.

In Sawmill Canyon, located near the eastern margin of the Tuolumne batholith, central Sierra Nevada, California, a series of petrologically and structurally complex, magmatic sheeted zones intrude older granodioritic units (Kuna Crest and equigranular Half Dome) and in one case truncate these units along a sharp contact. These sheeted zones (a) consist of numerous batches of (now frozen) magma, (b) display clear outward growth directions, (c) were actively deforming during and after emplacement resulting in magmatic folds, faults and multiple magmatic mineral fabrics, and (d) are the location of numerous, but localized magma flow structures (schlieren-bounded tubes, troughs, megacryst-rich pipes) and instabilities (load casts, flame structures, slumps, diapirs, ridge and pillar structures). Geochemical data indicate that the sheeted zones largely consist of magmas derived from the Half Dome granodiorite with some late Cathedral Peak granodiorite pulses, and with fractionation and flow sorting forming widespread layering in the above structures.We interpret these sheeted zones to record the pulsing of magma during propagation and expansion of opening-mode (Mode I), submagmatic fractures at the margins of large blocks of older, fairly solidified magmatic pulses that were subsequently removed from the present crustal level. Elsewhere in the Tuolumne batholith we see similar features suggesting that a “recycling” process, i.e., the breaking off of older parts of the magma chamber and incorporation into younger intrusive units, occurred in this batholith. This recycling removed a significant portion of older units and resulted in the formation of sheeted zones and local instabilities in this batholith. Finally this recycling is one process responsible for transfer of zircon crystals between units and for obscuring whole-rock geochemical signatures.

Finite strain analysis in the northern (Piute Meadow pendant (PMP)) and eastern (Saddlebag Lake pendant (SLP)) host rock pendants of the Tuolumne Intrusive Suite (TIS) reveals plane strain geometries in the pendants and a steep strain gradient in the SLP. Average regional z-axis shortening in both pendants is ca. 43% and increases to ca. 70 and 85% in the SLP within ca. 100m to the pluton contact. Microstructures in the SLP adjust to increasing temperatures and partial melting near the margin. Beyond the pluton margin, weakly elongate quartz grains with lobate grain boundaries, patchy to sweeping undulose extinction, deformation bands, and incipient subgrains are consistent with low-temperature dislocation creep. Towards the margin, quartz grain boundaries become increasingly irregular and display “chessboard” patterns indicating high-temperature dislocation creep. Grain size is markedly smaller near the margin and despite large finite strain grains do not show evidence for crystal-plastic deformation. Cuspate strain-free interstices are interpreted to mimic former anatectic melt. Outcrop-scale migmatization, coincidence with abruptly increasing finite strain, and microfracturing towards the margin implies that fracture-induced mechanical grain size reduction may have triggered the transition to melt-assisted granular flow, ultimately resulting in drastic rheological weakening.

The Rieserferner Pluton was emplaced at a depth of 12-15 km into steeply dipping, greenschist-facies mylonitic rocks of the Austroalpine basement, just south of the Tauern Window (Eastern Alps). Intrusion occurred during north-south-directed shortening and east-west horizontal extension in front of the rigid Southern Alpine Indenter. The regional strain field is transpressive, with a strong coaxial component, and is characterized by east-west stretching. Tonalitic melt ascended through a feeder channel preserved in the steep southern part of the Rieserferner Pluton, within and adjacent to the steep mylonitic foliation of a major shear zone, the Defereggen-Antholz-Vals (DAV) Line. Melt ascent was perpendicular to the north-south shortening direction in the country rocks. Magma emplacement involved melt-induced hydro-fracturing to form a subhorizontal, tabular pluton that protruded northward from the DAV Line into the previously folded country rocks. During the late stage of emplacement, buoyant upwelling of the partly recrystallized magma induced doming of the pluton roof as well as vertical ductile shortening of the directly overlying country rocks. Magma pressure therefore locally exceeded the lithostatic pressure. Thermal modeling constrains the maximum time for doming and solidification of the pluton to have been 32,000 yr. The wavelength of the domes in the pluton roof indicates the viscosity contrast between country rock and partly crystallized tonalite in the pluton to have been at least 100:1.

In this paper we model coupled spatial and temporal changes in stress and temperature to calculate dislocation creep strain rates in host rock associated with spherical magma chamber expansion with and without material removal by stoping and/or assimilation. Given a constant magma-chamber pressure of 100MPa, we show that stress and temperatures in the host rock range from 100 to 10MPa and 800 to 300°C, respectively. Using a flow law for dislocation creep of wet quartzite with recently calibrated parameters, maximum dislocation creep strain rates on the order of ca. 10−10s−1 occur only close to the pluton margin. Despite the simple geometry relative to real plutons, the models yield several thought-provoking predictions. If the outer portions of the pluton are allowed to cool, a wide thermal and structural aureole forms. Maintaining the liquidus temperature in the entire pluton allows for rapid aureole deformation, resulting in a narrow thermal and structural aureole, because the deformation outpaces heat conduction. Dislocation creep strain rates in the inner portions of aureoles are extremely sensitive to pressure changes only, potentially resulting in large transient variations in strain rate under isothermal conditions. Evidence for elevated strain rates in pluton aureoles may not be preserved in host rock aureoles if solidified pluton participates in the deformation or it may be completely removed.

Finite strain analysis and thermal modeling of magmatically folded leucocratic dikes in the Mount Stuart Batholith, Washington and the Tuolumne Intrusive Suite, California, yield strain rates in the range of 10(-2) to 10(-13) s(-1). Compared to published regional strain rates (10(-13) to 10(-15) s(-1)), wallrock strain rates associated with dike-fed expansion (10(-7) s(-1)), and rates resulting from numerical modeling of crystal-plastic creep in aureoles (10(-11) s(-1)), our fast rates are several orders of magnitude higher.Field and microstructural observations suggest that multiple material transfer processes, including rigid rotation, ductile flow, cracking, and potentially melt-assisted granular flow operated in the aureoles to accommodate emplacement of these two plutons. Calculated durations of pluton construction and bulk shortening in the aureoles indicate that aureole deformation requires only slow, long-term strain rates of 10(-14) s(-1). Thus our local fast strain rates indicate that aureoles may be characterized by pulsating high strain rate surges. We suggest that magmatically folded dikes in these and other pluton aureoles around the world may be used as evidence for fast host rock strain rates during pluton emplacement.