Gravity Spreading Research Articles

Salt-related gravity-driven processes in the Levant Basin, Eastern Mediterranean: Insights from physical modeling

The characterization of salt tectonics and its gravity-driven deformation processes are the key to a better understanding of the structural evolution of salt-bearing rifted margins. Unlike most salt basins that have experienced long-lasting deformation, the Messinian evaporites in the Levant Basin have been moderately deformed, offering the opportunity to study the early stage of salt tectonic deformation. Despite the availability of seismic reflection, borehole and bathymetrical data, some uncertainties still exist about the mechanisms responsible for the deformation and structural features observed in the deep-water Levant Basin. Our study includes physical experiments based on published seismic and structural interpretations conducted in the Levant Basin. Our physical experiments take into consideration the main driving parameters that controlled the development of the deep-water Levant Basin, testing the interplay and impact of gravity gliding and spreading from the Levant Margin, gravity spreading from the Nile Deep Sea Fan, and the influence of the passive buttress of the Eratosthenes Seamount. Deformation was imposed by depositing successive sand lobes and/or by tilting the experimental table. The physical models included a thick viscous silicone layer, analogue of the Messinian evaporitic sequence, overlain by a granular overburden, simulating the brittle clastic post-Messinian succession. Results show that the prominent gravity-driven force affecting the deformation pattern of the deep-water Levant Basin is the gravity spreading from the Nile Deep Sea Fan, whereas gravity spreading and gliding from the Levant Margin affect only the proximal to the margin areas. Additionally, the buttressing effect of the Eratosthenes Seamount and the location of the salt basin pinch-out played an important role in the final deformation pattern of this region of the Eastern Mediterranean.

The role of subduction and gravitational collapse in driving extension in the Aegean Sea

The Aegean domain has experienced lithospheric deformation during continuous northward subduction at the Hellenic trench. Early Cenozoic shortening and thickening were followed by late Cenozoic extension and thinning. Thickened lithosphere, in particular its crust, has excess gravitational potential energy, which is thought to promote orogenic collapse (i.e., gravity spreading). In the Aegean domain, release of this potential energy and collapse of the lithosphere has been proposed as the first-order driver for extension of the overriding plate. Here we show, using dynamically self-consistent analogue experiments of subduction and gravity spreading, that the subducting plate significantly influences overriding plate deformation, despite the overriding plate being positively buoyant. With the introduction of a subducting plate, the trench retreat velocity and overriding plate extension rate increase, which is in contrast with a continuous decline during gravity spreading. In addition, ∼E-W trending normal faults emerge, as opposed to arc-parallel faults trending ∼ENE-WSW to ∼ESE-WNW and arc-normal extensional zones that result from gravity spreading only. Similarly, the subducting plate causes overriding plate displacement to be unidirectional (trenchward), in accordance with the present-day geodetic velocity field, whereas gravity spreading causes a radially outward-directed displacement field. As the decline in trench retreat rate, radial spreading, dominantly arc-parallel normal faults, and arc-normal extensional zones are not observed in nature, this implies that gravity spreading cannot be the sole driver of extensional deformation in the overriding plate. Indeed, the models suggest that subduction-induced mantle flow is the dominant driver of overriding plate deformation because it imposes a basal shear stress on the overriding plate, dragging and extending it trenchward in a unidirectional manner. Our experimental results corroborate earlier studies that highlight the important role of subduction-induced mantle flow in driving overriding plate deformation. Additionally, we find that this role is more pronounced in experiments with a thicker brittle layer.

The effects of subsalt relief on gravity-driven salt tectonics: Results from analogue modelling

Gravity-driven salt-related deformation on passive margins is commonly interpreted as kinematically-linked domains of updip extension and downdip contraction with an intermediate, undeformed zone of translation. Our study uses analogue models to show how salt flow is affected by the subsalt geometry resulting in complex deformation and the alternation of extensional and contractional domains in space and time in translational salt provinces. In our work, the analogue models incorporate subsalt relief associated with half-graben and graben that are realistic geometries along passive margins and combine the effects of gravity spreading in which deformation is driven by differential sedimentary loading, and an early-stage of gravity gliding induced by basin tilt. This approach allows for analysis of how salt flow and overburden deformation are affected by: (1) smoothly dipping subsalt relief; (2) subsalt relief characterized by half-graben with a gently landward dipping extensional fault; (3) subsalt half-graben connected laterally with a distal symmetric graben. For each of these models, we evaluate: 1) the interplay between slipping deformation corresponding to gravity gliding, gravity spreading mechanisms, and subsalt geometry; 2) the spatial and temporal distribution of salt-related structural domains; and 3) the contrasting styles of salt tectonics for different subsalt geometries. In addition, some of the experiments have been repeated considering thicker salt and pre-kinematic overburden and different sedimentation rates. We show that the structures of the subsalt relief variably resist salt flow producing flow mismatch. This variable resistance controls the orientation of the extension and contraction supra-salt structures. Salt surplus and contraction occur over landward dipping base-salt ramps, and a zone of salt depletion and subsidence limited by extensional and contractional hinges occurs over the basinward dipping base-salt ramp. Variations in width and the dip of these base-salt ramps result in stronger flow mismatches and deformation complexity. We also discuss variations in salt flow profile in response to the gravitational forces that drive deformation, allowing a good first-order approximation of viscous salt flow at a regional scale that can be directly compared to examples from various salt-bearing continental margins, particularly the relatively less understood but extremely economically important distal domains of Brazil's Campos and Santos basins.

Kinematic Response of Subaerial Salt Diapirs to Geomorphic, Tectonic and Climatic Regimes: Insights From Space‐Based Observations in the Western Kuqa Fold‐Thrust Belt, NW China

AbstractEphemeral subaerial salt diapirs are gravitationally unstable and vulnerable to climate and tectonic activity due to the rheology and incompressibility of rock salt. Quantifying the kinematics of subaerial salt and clarifying the role of tectonics, surface processes, and climate in reshaping the surface salt morphology provides an invaluable opportunity to explore the interactions between Earth’s spheres on a much shorter timescale. With diverse exposed salt diapirs and potential motions, the Kuqa fold‐thrust belt (KFTB), NW China, represents an optimum natural laboratory to understand subaerial salt kinematics. Here, we integrated ascending and descending geometries of Sentinel‐1 synthetic aperture radar images with optical remote sensing data, seismic profiles, digital elevation models, and meteorological records to explore the potential correlation between subaerial salt motions and geomorphic, tectonic, and climatic factors. Using the interferometric synthetic aperture radar technique, we observed a maximum of 25 mm/yr in vertical and 40 mm/yr in horizontal surface salt deformation in the KFTB from 2014 to 2020. Our findings demonstrate a gravity spreading dominant system, where topography exerts a primary control on the surface displacement patterns of salt structures, while weather variables influence deformation mainly by softening salt and facilitating gravity‐driven salt flow.

Structural architecture and evolution of eastern Mississippi Canyon, northern gulf of Mexico

3-D, depth-migrated seismic data are used to evaluate the structural architecture and evolution of eastern Mississippi Canyon, northeastern Gulf of Mexico. The W-dipping base of the Louann salt is mostly unfaulted, such that basement faults did not influence Late Jurassic to Recent deformation. Instead, the suprasalt evolution was driven by a combination of lateral (gravity-driven) and vertical (differential loading) forces that varied in importance and direction over time. Salt movement was initiated in the Late Jurassic by SW-directed, convergent gravity gliding on an arcuate margin. This resulted in both contractional thrust faults and folds and dome-and-basin structures that set up the initial configuration of minibasins, salt plateaus, and early diapirs. The minibasins evolved as either turtle structures or expulsion-rollover structures, with the distribution of the two defining a convergent Mesozoic paleo-slope and age-equivalent basin floor. Gravity-driven deformation waned and differential loading gradually became more important during this time. The relative interplay between the two drivers reversed again during the Miocene due to a combination of progressive welding of the Louann salt and an eastward shift of Miocene deltaic shelf edges updip of the study area. The latter triggered SSE-directed gravity spreading, with most of the resultant extension and contraction located in more proximal and distal areas, respectively. The study area was mostly in the translational domain, which was bounded by a zone of sinistral strike-slip deformation downdip of the lateral edges of the deltaic depocenters. Miocene salt structures defined two provinces: a proximal domain characterized by counterregional feeders and basinward-flowing salt sheets; and a distal domain with vertical feeders and radially-spreading allochthonous salt. The boundary between the two marked the Miocene toe of slope. Lessons derived from the study area can be applied to help understand the more complex structures and evolution farther west in the northern Gulf of Mexico.

Shale mobility: From salt-like shale flow to fluid mobilization in gravity-driven deformation, the late Albian–Turonian White Pointer Delta (Ceduna Subbasin, Great Bight, Australia)

Large offshore depocenters above a weak detachment level (either salt or shale) can undergo gravity spreading and/or gliding. The gravitational systems (e.g., gliding deltas) are classically composed of an updip domain affected by extensional listric normal faults and a downdip domain affected by toe thrusts. While the role of salt in such systems is a classic tectonic process, the role and mechanical behavior of mobile shale levels in shale-prone gravity-driven systems are increasingly questioned. A three-dimensional seismic data set in the Ceduna Subbasin (Australia) displays the late Albian–Turonian White Pointer Delta (WPD) as having an unusual diversity of shale-cored structures. The early flow of shale resulted in depocenters showing wedges, internal unconformities, and shale diapirs and ridges, while fluidization of shales underneath a significant burial resulted in mud volcanism, secondary radial fault sets, and collapse features beneath the Campanian–Maastrichtian Hammerhead Delta, which lies above the WPD. Massive shale mobilization, together with downdip shortening and distal margin uplift, localized a major thrust in the core of the basin, ending the downward-propagating failure of the WPD. Mobilization of thick shale intervals, either as salt-like flow or mud volcanism, appears to have been a key process in the deformation, which should be considered at large scale for worldwide gravity-driven deformation systems.

Shale mobility: From salt-like shale flow to fluid mobilization in gravity-driven deformation, the late Albian–Turonian White Pointer Delta (Ceduna Subbasin, Great Bight, Australia)

Abstract Large offshore depocenters above a weak detachment level (either salt or shale) can undergo gravity spreading and/or gliding. The gravitational systems (e.g., gliding deltas) are classically composed of an updip domain affected by extensional listric normal faults and a downdip domain affected by toe thrusts. While the role of salt in such systems is a classic tectonic process, the role and mechanical behavior of mobile shale levels in shale-prone gravity-driven systems are increasingly questioned. A three-dimensional seismic data set in the Ceduna Subbasin (Australia) displays the late Albian–Turonian White Pointer Delta (WPD) as having an unusual diversity of shale-cored structures. The early flow of shale resulted in depocenters showing wedges, internal unconformities, and shale diapirs and ridges, while fluidization of shales underneath a significant burial resulted in mud volcanism, secondary radial fault sets, and collapse features beneath the Campanian–Maastrichtian Hammerhead Delta, which lies above the WPD. Massive shale mobilization, together with downdip shortening and distal margin uplift, localized a major thrust in the core of the basin, ending the downward-propagating failure of the WPD. Mobilization of thick shale intervals, either as salt-like flow or mud volcanism, appears to have been a key process in the deformation, which should be considered at large scale for worldwide gravity-driven deformation systems.

Salt geometry in the Central Basin of the Nova Scotia passive margin, offshore Canada based on new seismic data

This study describes the structural architecture of the central portion of the Scotian Basin and focusses on Mesozoic salt deposition and deformation linked to magma-rich rifting. BP acquired a high-quality 3D seismic survey called the Tangier survey and built a detailed velocity model with RFWI (Reflection Full Waveform Inversion) and tomography. This has allowed for high resolution seismic imaging of target sedimentary reservoirs but also for the first time, imaging of the complex crustal architecture along the central part of the Nova Scotia margin. We evaluated the regional basin architecture and salt tectonic evolution in context of Late Triassic and Early Jurassic rifting followed by passive margin gravity spreading. An exploration well (Aspy D-11) was drilled based on the 3D seismic interpretation and penetrated halite, carnallite and anhydrite salt in an allochthonous salt sheet. Basement is thought to have rifted during deposition of interlayered halite, shale, carnallite and anhydrite. Carnallite may have precipitated from enriched brines that formed at the more distal (southern) end of an elongated seaway of rifted basins which began opening first in the North in the Late Triassic and propagated southward towards Florida (e.g., Jansa, 1980; Jansa and Tucholke, 1986; Roberts and Bally, 2012). Water flowed southwards from Tethys along a chain of complexly interconnected areas of rifted basins. Flow of seawater along Nova Scotia is interpreted to have been southward along a widening and progressively subsiding region of rifts possibly as dynamic elevation associated with the CAMP (Central Atlantic Magmatic Province) dissipated southward much like what occurred in the Central South Atlantic and Gulf of Mexico (GoM) (e.g., Quirk et al., 2013; Morgan et al., 2020; Pindell et al., 2020; Pindell and Heyn, 2022). Brine was enriched along the seaway by evaporation, causing deposition of the most-soluble salt components furthest south along the sequence of basins. The presence of weathered basalt in salt and SDRs on the seismic supports magma-rich Mesozoic rifting and suggests that heating of brine pools may not have been exclusively caused by the sun, but that hydrothermal systems probably contributed to heating and the precipitation of Carnallite.

Integration of satellite gravimetry, multispectral imagery and digital elevation model for investigating crustal deformation in the Niger Delta Basin

Remotely acquired gravity data from satellite gravimetry is integrated into the study to investigate crustal deformation in the Niger Delta Basin. The Niger Delta Basin is a well-documented example of a passive margin delta that has gravitationally deformed. The gravity-driven deformation has not been fully understood, and new trends may be emerging. In this study, we assess and delineate structural deformation and sediment accumulation of the Agbada and Akata stratigraphic sequences within the basin's prograding clastic wedge. This was done through the integration of data from the Gravity Recovery and Climate Experiment (GRACE) mission, Landsat 8 satellite imagery, and the Advanced Land Observation Satellite (ALOS) World 3D-30 m (AW3D) DEM. The methodology workflow incorporated gravity modelling from GRACE data, lineament extraction from Landsat imagery, and drainage network analysis from the AW3D DEM. The Niger Delta Basin as seen on the gravity models depicts large-scale block faults with a well-defined graben structural topography. This eventually shows that the basin is dominated by growth faulting with differential subsidence. The predominant directions of the mapped lineaments are in the N-S and W-E directions. With over 18,500 lineaments, the W-E direction is marginally the dominant direction of the two predominant directions. Many linear structures such as shear zones and fractures which have different orientations and directions characterise the study area. Also present are the minor N-S fractures which are attributed to brittle deformation and sets of NE-SW and NW-SE trends, produced by transcurrent movements as the structural framework of the Nigerian basement complex are dominated by the NE-SW lineaments. However, the complexity in the structural geometry and thrusting sequences in the Niger Delta shows the patterns of growth structure and imbricate thrusting. The structural pattern also exhibits outward radial gravity spreading of dip-orientated, extensional structures that include delta slope radial grabens and tear faults. Radial spreading has likely increased the segmentation of Niger Delta regional depo-belts in the N-S direction. It is observed that most of the structural deformations in the basin are syn-formational, evolving at the same time as sediment deposition.

Thin-skinned extensional salt tectonics, counterregional faults, and the Albian Gap of Brazil

Thin-skinned extension detached on salt is mostly well understood. Faults may dip basinward or landward (counterregional) and intersect the top salt or equivalent weld at cusps/rollers. The polarity of faulting may switch over time, and with sufficient extension, the oldest suprasalt strata separate into rafts with intervening younger depocenters. Salt may break through extensionally thinned overburden to grow as passive diapirs, which can widen during ongoing extension but collapse if the salt supply cannot keep pace with extension. Counterregional normal faults are the most debated structures as they may form by: extension, with the footwall moving basinward relative to the hanging wall; or progressive basinward salt expulsion but only vertical movement of the overburden. Extensional counterregional structures are characterized by: (i) strata that predominantly thicken into the bounding structures, but with areas of basinward thinning due to fault/salt geometry and displacement transfer; (ii) highly elongate plan-view geometries; and (iii) the presence of coeval distal translation and contraction. The most controversial counterregional system is the Albian Gap of the Santos Basin, Brazil. We use the criteria above to argue that it formed by post-Albian thin-skinned extension, with little/no extension during the Albian. This contrasts with the Campos Basin along strike to the NE, where Albian and later extension were accommodated on basinward-dipping faults, and is explained by the rift architecture and consequent base-salt dip. The Aptian salt dipped basinward in the Campos Basin and extension was therefore triggered by Albian gravity gliding. However, the base salt dipped landward over a large area of the northern and central Santos Basin, so that Albian gravity gliding was minimal and Late Cretaceous progradational loading drove gravity spreading and the development of the counterregional system. Accommodation for sediment within the Albian Gap was provided in part by stretching and consequent thinning of the underlying salt.

Lava Dome Morphology and Viscosity Inferred From Data-Driven Numerical Modeling of Dome Growth at Volcán de Colima, Mexico During 2007-2009

Magma extrusion, lava dome growth, collapse of domes, and associated pyroclastic flow hazards are among important volcanological studies. In this paper, we analyze the influence of the magma viscosity and discharge rates on the lava dome morphology at Volcán de Colima in Mexico during a long dome-building episode lasting from early 2007 to fall 2009 without explosive dome destruction. Camera images of the lava dome growth together with recorded volumes of the erupted lava have been used to constrain numerical modeling and hence to match the history of the dome growth by nudging model forecasts to observations. Our viscosity model incorporates crystal growth kinetics and depends on the characteristic time of crystal content growth (or CCGT) and the crystal-free magma viscosity. Initially, we analyze how this viscosity, CCGT, and the rate of lava extrusion influence the morphology of the growing dome. Several model scenarios of lava dome growth are then considered depending on the crater geometry, the conduit location, the effective viscosity of dome carapace, and the extrusion rates. These rates are determined either empirically by optimizing the fit between the morphological shape of modeled domes and that of the observed dome or from the recorded lava dome volumes. The maximum height of the modeled lava dome and its horizontal extent are in a good agreement with observations in the case of the empirically-derived extrusion rates. It is shown that the topography of the crater at Volcán de Colima is likely to be inclined toward the west. The viscosity of the modeled lava dome (∼1012 Pa s) is in a good agreement with the effective viscosity estimated experimentally from lavas of Volcán de Colima. Due to the interplay between the lava extrusion and the gravity forces, the dome reaches a height threshold, and after that a horizontal gravity spreading starts to play an essential role in the lava dome evolution. The model forecasts that the dome carapace of higher viscosity (∼1014 Pa s) influences the dome growth and its morphology during long dome-building episodes by retarding horizontal advancement and developing steep-sided eastern edge of the dome at the volcano. The developed model can be used in assessments of future effusive eruptions and lava dome growth at Volcán de Colima or elsewhere. History matching modeling of lava dome growth sheds a light on dynamic processes inside the dome and may assist in assessing stress state in the dome carapace and in forecasting the dome failures.

Gravity-driven deepwater fold-and-thrust belts as Critical Coulomb Wedges: Model limitations and the role of friction vs. fluid pressure

Gravity-driven Deepwater Fold-and-thrust Belts (GDFB) are the result of gravitational collapse of the sedimentary pile along the continental shelf. These systems can be described in the framework of the Critical Coulomb Wedge (CCW) mechanics to infer their mechanical properties and hydrological conditions. However, not all GDFB can be considered as critical wedges and their mechanical/hydrological parameters should be critically assessed. GDFB driven by gravity spreading and detached onto brittle overpressured shales are the most suitable systems to be modeled via the original CCW theory. In addition, the self-limiting mechanism of gravitational collapse implies that GDFB can reach the critical state only during limited time intervals (in some cases less than ∼10 Myr), in the presence of large sedimentary loads and shortening rates higher than 1.5–2 mm/yr. We present a compilation of GDFB that most likely represent examples of critical tapers, almost exclusively located downdip of large deltas. We then analyze several analytical solutions to the CCW equation, constrained by laboratory and geophysical data, to discuss the role of material friction and fluid pressures in GDFB. Low friction and moderate fluid overpressure localized in the basal detachment are both essential to explain the observed shape of GDFB. Frictional and overpressure discontinuities between detachment and the overlying wedge are likely to be maintained in GDFB.

Tectono‐stratigraphic evolution of the offshore western Niger Delta from the Cretaceous to present: Implications of delta dynamics and paleo‐topography on gravity‐driven deformation

AbstractThe interaction between sedimentary wedge dynamics and paleo‐fracture zones is investigated offshore western Niger Delta lobe (WNDL) to reconstruct the evolution of the delta from the Cretaceous to present. This was achieved through detailed regional seismic interpretation, calibrated with well data. Our results suggest that high sedimentation rates in the WNDL since the Serravallian–Tortonian triggered the migration of the ‘Oligocene‐Tortonian extensional zone’ and gravity spreading seawards (from a present‐day onshore to a present‐day offshore position), with extensional, translational and contractional deformation. An additional increase in sedimentation rate since the early Pliocene, further accelerated gravity spreading and the development of the present‐day contractional front. A five‐stage tectono‐stratigraphic evolution of the offshore WNDL from the late Cretaceous to present is proposed. Paleo‐topographies formed by the Charcot and Chain Fracture Zones exerted depositional control on the stratigraphic architecture of the offshore WNDL from the Cretaceous to Serravallian. Differential subsidence on both sides of the relict Charcot and Chain transform faults is responsible for the segmentation of gravity‐driven deformation of the eastern and western Niger Delta lobes. In addition, a comparison of the stratigraphic architecture of the eastern Niger Delta lobe (ENDL) and WNDL demonstrates a similar overall progradation and sediment bypass to the deep basin during the Pliocene. During the Pleistocene, the two lobes show a distinct evolution and architecture: the ENDL shows an overall retrogradation and sediment sequestration on the shelf, whereas the WNDL displays an overall progradation and sediment bypass. This study documents long‐term and large‐scale control of delta dynamics and paleo‐topography on gravity‐driven deformation of the offshore eastern and western Niger Delta lobes, and similar analysis could be applied in the reconstruction of other passive margin basins.

Structures in Shallow Marine Sediments Associated with Gas and Fluid Migration

Geological structure changes, including deformations and ruptures, developed in shallow marine sediments are well recognized but were not systematically reviewed in previous studies. These structures, generally developed at a depth less than 1000 m below seafloor, are considered to play a significant role in the migration, accumulation, and emission of hydrocarbon gases and fluids, and the formation of gas hydrates, and they are also taken as critical factors affecting carbon balance in the marine environment. In this review, these structures in shallow marine sediments are classified into overpressure-associated structures, diapir structures and sediment ruptures based on their geometric characteristics and formation mechanisms. Seepages, pockmarks and gas pipes are the structures associated with overpressure, which are generally induced by gas/fluid pressure changes related to gas and/or fluid accumulation, migration and emission. The mud diapir and salt diapir are diapir structures driven by gravity slides, gravity spread and differential compaction. Landslides, polygonal faults and tectonic faults are sediment ruptures, which are developed by gravity, compaction forces and tectonic forces, respectively. Their formation mechanisms can be attributed to sediment diagenesis, compaction and tectonic activities. The relationships between the different structures, between structures and gas hydrates and between structures and authigenic carbonate are also discussed.

The Volsci Volcanic Field (central Italy): eruptive history, magma system and implications on continental subduction processes

Here, we report on the Quaternary Volsci Volcanic Field (VVF, central Italy). In light of new 40Ar/39Ar geochronological data and compositional characterization of juvenile eruptive products, we refine the history of VVF activity, and outline the implications on the pre-eruptive magma system and the continental subduction processes involved. Different from the nearby volcanic districts of the Roman and Campanian Provinces, the VVF was characterized by small-volume (0.01–0.1 km3) eruptions from a network of monogenetic centers (mostly tuff rings and scoria cones, with subordinate lava occurrences), clustered along high-angle faults of lithospheric depth. Leucite-bearing, high-K (HKS) magmas (for which we report for the first time the phlogopite phenocryst compositions) mostly fed the early phase of activity (∼761–539 ka), then primitive, plagioclase-bearing (KS) magmas appeared during the climactic phase (∼424–349 ka), partially overlapping with HKS ones, and then prevailed during the late phase of activity (∼300–231 ka). The fast ascent of primitive magma batches is typical of a tectonically controlled volcanic field, where the very low magma flux is a passive byproduct of regional tectonic strain. We suggest that the dominant compressive stress field acting at depth was accompanied by an extensional regime in the upper crust, associated with the gravity spreading of the Apennine chain, allowing the fast ascent of magma from the mantle source with limited stationing in shallow reservoirs.

3D simulations of salt tectonics in the Kwanza Basin: Insights from analogue and Discrete-Element numerical modeling

The Kwanza Basin is located at the passive margin of West Africa in the Central Segment of the South Atlantic, and is an important area for oil and gas exploration. The distribution and deformation characteristics of thick Lower Cretaceous (Aptian) salt deposits in the basin have significant impacts on hydrocarbon accumulation. However, reports on their 3D interpretation, together with an understanding of the genesis and evolution of salt tectonics in this area, are scarce in the literature. In this paper, 3D analogue experiments and 3D Discrete-Element numerical simulations are carried out to analyze the zonal characteristics (extension-translation-contraction), the main control factors, and to develop a kinematic model of salt tectonics in the basin. According to our modeling, we make the following conclusions. (1) The zonal characteristics of salt tectonics formed in the basin reflect the superposition of gravity gliding and gravity spreading. The main control factor of basin-scale salt deformation is basement structural activity, which can be summarized into three points: early post-salt basement extension, initial presence of local variation of base of salt gradient and more recent differential subsidence between landward side and seaward side. (2) Salt deformation is episodic, having experienced one stage of regional deformation (Late Aptian to Albian) and two stages of inherited developmental deformation (Campanian, and Eocene to Miocene), mainly resulting in forward expansion towards the ocean. (3) During the early stage of salt deformation, faults developed in suprasalt layers in the extensional and translational zones of the basin, resulting in local high-velocity areas and a large vertical upward velocity component in the salt layer. Later, due to blocking by the outer high region and increasing overburden, salt in contact with the outer high developed a vertical upward velocity component, gradually forming thrust structures. (4) 3D analysis highlights the pervasive lateral deformation of the salt. The main factors governing it are the distribution of accommodation in the salt basin and the initial morphology of the salt layer. In the early stages, salt layer had a velocity component to the salt-scarce side (from north to south), whereas in the later stages, it developed a velocity component to the wide side of the basin (from south to north), leading to the gradual accumulation of salt in the north of the basin. We have shown that 3D simulations can complete the analysis of salt deformation both parallel and perpendicular to the slope in a passive-margin basin. This may provide guidance for the exploration of oil and gas reservoirs in the context of salt tectonics, especially in asymmetrical basins where seismic imaging is poor and has to be supplemented by strong geological concepts including understanding 3D movement of salt.

Tectonics and foreland basin development at the leading edge of the Humber Arm Allochthon, western Newfoundland, Canadian Appalachians

The thrust front of the Northern Appalachians involves Ediacaran rift-related structures of the Laurentian margin that were re-worked in Taconic (Ordovician), Salinic (mainly Silurian) and Acadian (mainly Devonian) deformation events. Much of the thrust front is concealed under the Gulf of St. Lawrence, but Port au Port Peninsula, in western Newfoundland provides a cross-section through the Laurentian passive margin, overlying foreland basins, and the Humber Arm Allochthon. A large area of foreland basin strata is present in areas formerly mapped as Humber Arm Allochthon. Abrupt thickness changes and an abundance of fault-scarp-derived limestone conglomerate indicate that deposition was influenced by block faulting and differential subsidence in a basin undergoing active flexural extension. A coarsening upward trend in the Goose Tickle Group represents a transition from a distal to a proximal sediment source as the Humber Arm Allochthon was emplaced westwards. Goose Tickle Group separates two packages of allochthonous rocks. The West Bay Thrust Sheet, the lower package, represents the leading edge of the Taconic allochthon. Its timing of emplacement is constrained by Darriwilian 3 graptolites both above and below the thrust sheet. Its present-day configuration results from a combination of processes including thrusting, extension by gravity spreading, gravity gliding, and subsequent erosion of material that was deposited in the Goose Tickle Group. The structurally higher Lourdes Thrust Sheet is an out-of-sequence structure associated with Acadian (Devonian) orogenesis. High-angle faults show a protracted history of movement that includes early Taconic flexural extension, Acadian inversion, and later Carboniferous or Mesozoic strike-slip motion. The leading edge of the Humber Arm Allochthon was influenced by both thin-skinned and thick-skinned tectonics throughout the development of the Appalachian orogen.

Characterization of mass transport deposits using seismic attributes: Upper Leonard Formation, Permian Basin

The Permian Basin is a structurally complex sedimentary basin with an extensive history of tectonic deformation. As the basin evolved through time, sediments dispersed into the basin floor from surrounding carbonate platforms leading to various mass movements. One such mass movement is observed on a 3D seismic survey in the Upper Leonard interval (Lower Permian) of the Midland Basin that is characteristic of a mass transport deposit (MTD). The 350 ft thick MTD mapped in the study area is 5 mi wide, extends up to 14 mi basinward, and covers only the translational and compressional regime of the mass movement. A unique sedimentary feature, unlike those observed previously, is mapped and interpreted as gravity spreading. MTDs have been extensively studied in the Delaware Basin of Permian-aged strata; however, only a few works have been published on the geomorphological expression of MTDs using seismic and seismic attributes to delineate the shape, size, and anatomy of this subsurface feature. The MTD in the study area exhibits an array of features including slide, slump, basal shear surface, and MTD grooves. In cross section, the MTD is characterized as chaotic with semitransparent reflectors terminating laterally against a coherent package of seismic facies, or the lateral wall. Sobel filter-based coherence, structural curvature, dip magnitude, and dip azimuth attributes are used to map thrust faults within the discontinuous MTD. Kinematic evidence provided by the Upper Spraberry isopach suggests that this MTD was sourced north of the Midland Basin and deposited on the basin floor fairway. Slope strata are interpreted from well-log analysis showing MTD as a mixture of carbonates and siliciclastics with a moderate to high resistivity response.

The evolution of a gravity-driven system accompanied by diapirism under the control of the prograding West Luconia Deltas in the Kangxi Depression, Southern South China Sea

Gravitational collapse structures are commonly observed in shelf-margin deltas underlain by mobile shales. However, these structures are rarely accompanied by mud diapirs. This paper presents an updated study of the gravity-driven system in the West Luconia Deltas, a shelf-margin delta system, in the Kangxi Depression, southern South China Sea. Compared to the classical shale-detachment model, the syn-collapse deformation in the contractional domain in this study is accommodated mainly by thrust faults combined with mud diapirs rather than simply imbricated thrusts. Based on seismic interpretation and structural analysis, this gravity-driven system is divided into three domains, the extensional domain, the contractional domain and the transitional domain. All of these domains are intruded by mud diapirs. The quantitative analysis of the amounts of extension and contraction suggests that these structures mainly resulted from gravitational collapse rather than the tectonic compression. Quantification of the relative contributions of gravity spreading and gliding indicates that the gravitational collapse was mainly driven by gravity spreading. Two episodes of collapse are suggested by the analysis of the progradation of the West Luconia Deltas and the features of the syn-collapse structures. The first episode was minor and not accompanied by diapirism, whereas the second episode was major and accompanied by diapirism. The entire evolution of the GDS is divided into five stages: (1) the first episode of the gravitational collapse, lasted from the earliest Middle Miocene to the earliest Pliocene; (2) the deposition of an interval between the syn-collapse strata and the mobile shale, occurred in the Early Pliocene.; (3) the initiation of the second episode of the gravitational collapse, lasted from the Early Pliocene to the Late Pliocene; (4) the attenuation and basinward migration of the gravity-driven deformation, lasted from the Late Pliocene to the Early Pleistocene; and (5) the ending of the gravitational collapse, lasted from the Early Pleistocene to the present. The last four stages were accompanied by intensive diapirs which pierced the overlying strata and became targets for the hydrocarbon exploration.

Large-scale deformations in Neogene deposits near Dobrzyń on the Vistula (central Poland) – thrusting from N/NE or valley-side glaciotectonics in the Płock Basin?

The article is focused on the most recent investigations of glaciotectonic structures in high escarpment exposures of the Vistula valley from Dobrzyń to Kuzki in the western part of the Płock Basin. Deformations involve Neogene and occasionally the Lower Pleistocene deposits and they are not expressed as landforms. Structural investigations and analysis of archival geological data provided new information on the origin of large-scale shear structures. Results obtained are clearly contrary to the concept of Brykczyński (1982) regarding valley-side glaciotectonics in the Płock Basin. An emergence of the extensive zone of serial thrust structures of significant amplitude (up to 100–150 m) was found to have not been controlled by a palaeovalley. A driving mechanism is interpreted as a gravity spreading in front of ice sheets advancing from north-northeast during the South Polish Complex (Dorst-Elsterian).