Halokinetic Sequences Research Articles

Structural evolution of the Handun salt diapir, Zagros fold and thrust belt, southern Iran

The Fars region, in the Zagros fold and thrust belt, hosts a wide range of diapirs piercing over 10 km of stratigraphic sequence. Comprising Precambrian to Early-Cambrian Hormuz Salt, these diapirs exhibit a prolonged history of evolution. Outcrop evidence for understanding the diapir deformation history is mostly limited to the Cenozoic contractive phase, and the seismic data lacks the necessary quality for an exhaustive understanding of the deepest structure's geometries. Through regional and field evidence we unravel the Handun salt structure evolution and propose a sequential restoration to describe the key deformational events. Our study presents a field-based novel regional balanced cross-section and a 3D-geological model, and addresses the role of structural inheritances and the position of the Handun diapir with respect to the decupled basement. The performed field studies describe folds and unconformities related to Cenozoic halokinetic sequences with exceptional clarity. It was possible to observe changes of the diapir activity along the structure and provide field evidence for the relative timing and kinematics of primary and secondary welding. Finally, our data suggest that the Handun diapir formed in the early Paleozoic above the shoulder of a basement extensional fault, and was partially translated above its southern hanging-wall during the shortening. In the Paleocene a sustained ratio of salt rise rate was enhanced by the Zagros/Oman contraction. In response to the Oligocene continental collision, the diapir was profusely supplied with salt, which flared upward to form overhangs. Since the middle Miocene the salt supply slowly depleted, with the diapiric walls remaining near the surface but tapering upward, probably due to primary welding or increased sedimentation. Secondary welding occurred post-Pliocene in the last stages of the diapir evolution with consequent development of a secondary minibasin.

Late quaternary morpho-stratigraphic record of diapir rise in the Cardona salt extrusion, NE Spain. Halokinetic sequences, raised terraces and uplift rates

Active diapirism has received very limited attention from the geomorphological and Quaternary Science perspective, despite the role played by this ground deformation process in the development of landforms and sedimentary environments, and the important practical implications associated with mobile salt structures (e,g., mining, hydrocarbon production, geostorage). The Cardona salt extrusion (NE Spain) was initiated in late Quaternary times from the post-shortening unroofing of the crest of a salt anticline by the entrenchment of the transverse Cardener River. Detailed mapping, outcrop analysis, geophysical data and trenching indicate that the diapir-flanking deposits show halokinetic complexes comprising two types of morpho-stratigraphic units: (1) an older flap of coarse-grained drapefolded colluvial deposits; and (2) younger lacustrine and fluvial deposits in peripheral depressions confined between the upturned colluvial flaps and the country rock slope. These synkinematic units record an overall relief inversion and correspond to the so-called wedge and hook halokinetic sequences, recording ratios between diapir rise rate and sedimentation rate lower and greater than 1, respectively. The radiocarbon ages obtained from several raised late Holocene strath terraces carved in the salt indicate uplift rates within the range of 36.5–12.1 mm/yr, consistent with geodetic data. The spatial variability of the uplift rates can be related to increasing flow rates towards the axis of the salt wall and potential along-strike variations. The relatively high diapir rise rates observed at Cardona diapir, unaffected by contractional displacement loading (tectonic squeezing), is attributed to the youthful stage of the salt extrusion and the low dynamic viscosity of the Cardona Saline Formation, with a low proportion of impurities and a significant amount of potash salts.

Growth of a salt diapir in an anticline - A record from the Cenozoic halokinetic sequences in the Zagros Fold and Thrust Belt, Iran

Salt diapirs in southern Iran provide excellent exposures of the host rock sedimentary sequences that record salt diapiric growth in compressional settings. This study addresses the reactivation of one particular diapir in the core of an anticline of the Zagros Fold and Thrust Belt (ZFTB) using the classical concept of halokinetic sequences. These sequences reflect the relative rise of the salt diapirs with respect to the depositional rate of the sediments in their surroundings. The resulting reconstruction indicates irregular deposition of the total eight sets of host rock sedimentary packages around the diapir during the Oligocene-Miocene that developed in response to the progressive rise of the host anticline. Folding of host rocks was associated with vertical movement of blocks bounded by cross-faults radiating from the boundary of the diapir, specifically around the triangular indenter on the north, deflecting the anticline to a southward advancing salient. The halokinetic sequences record an early stage of diapiric rise in the rhythmic alternation of gypsum and fossiliferous carbonate with siliciclastic material followed by fossiliferous limestone typical for lagoonal to slope environment in a limestone reef setting. The last stage is associated with thin-skinned tectonics of the uppermost halokinetic sequences thrust towards the diapir. Rapid thickness change of the halokinetic strata along the periphery of the diapir in the southern sector that includes also the crestal region of the anticline indicates compressional reactivation of the structure as early as 11 Ma (Gachsaran Formation), likely associated with salt overflow in the anticline crestal region, where the adjacent halokinetic sequences are completely overturned.

A new look at old debates about the Corbières (NE-Pyrenees) geology: salt tectonics and gravity gliding

In the Corbières area, a large-scale nappe has been identified at the beginning of the 20th century: the “Nappe des Corbières Orientales” (NCO) resting over a thick Triassic sole. This geological object is located at the NE of the Pyrenees, close to the Gulf of Lions. At this place, the chain changes in orientation from E-W to NE-SW and presents in detail, a great complexity. The existence of the nappe itself has never been contested. However, due to its overall complexity, several controversies exist regarding the style and chronology of deformation of its substratum in the so-called the “Pinède de Durban” in particular. We show that the new concepts of salt tectonics can clarify these old debates. Indeed, the rise of the Triassic salt during Mesozoic rifting episodes results in the development of characteristic sedimentary sequences (halokinetic sequences) on top of salt walls. It is along one of these, coinciding with the prolongation of the Cévenole Fault System, that the NCO has been individualized. During its Cenozoic emplacement, a gravity-gliding component, explaining the importance of the observed translation, could result from an uplift preceding the rifting at the origin of the Gulf of Lions.

Matrix deformation and fracture network in minibasins in a foreland fold and thrust belt: The Sivas Basin, Turkey

We use a multiscale study to investigate the strain record in the continental sandstones-filled minibasins of the Sivas Basin. Located on the central Anatolian Plateau, the Sivas basin is a foreland fold-and-thrust belt characterized in its central part by a wall and basin province in which two generations of Oligocene minibasins develop. We collected 399 oriented cores and 2504 fractures in the lower and middle members of the continental Karayün Formation from four minibasins (Emirhan, Karayün, Egribuçak and Ilkindi). Integrated analyses support several observations: (i) an early fracture set, striking NS, occurs in all minibasins. These fractures developed prior to macroscopic halokinetic structures formation (such as megaflap) and prior to minibasin tilting, during Layer Parallel Shortening (LPS). (ii) A preferential orientation of matrix texture, estimated using anisotropy of magnetic susceptibility, is related to the LPS direction only in the Emirhan minibasin. (iii) A second, younger, fracture set, oriented parallel to the tilting axes of the minibasins and to the thrust faults, developed prior to minibasin tilting or folding of minibasin edge structures (known as megaflaps, megahooks and composite halokinetic sequences). The existence of the carapace above raising salt bodies enables the propagation of the LPS deformation in response to regional shortening. However, once the carapace is broken due to the salt rise, there is no evidence of deformation at the meter and matrix scales in relation with FTB shortening affecting the wall and basin domain. The large bodies of evaporites preferentially accommodate compression in between minibasins through internal diapir squeezed. Salt bodies inhibit matrix and mesoscale deformation within the minibasins.

Analogical simulation of salt flow and associated structures in different extensional conditions

The salt layer thickness variability and the timing of salt deposition in relation to rifting (prerift salt, synrift salt, and late synrift/postrift salt) influence salt flow and the resulting growth, geometry, and kinematics of salt bodies under different extensional conditions. We apply analogue modelling to analyze the influence and interplay of each of these parameters through three series of experiments focusing on extensional salt tectonics. The first (Series I) simulates thick-skinned extension of a tabular salt layer in the absence of basement structures and explore the effects of variable salt thicknesses and extensional structural styles. Series II tests the degree of mechanical coupling of sub- and supra-salt faults according to contrasting salt thicknesses over a rotating rift block. Series III explores thin-skinned, gravity-driven deformation implementing models of i) pure-gliding (S1), ii) pure-spreading (S2) and iii) a combination of both (S3). Series I shows that the degree of symmetry and the kinematics of the structures vary due to the influence of the thickness of the salt layer. Thick salt layers tend to nucleate symmetric rifts and associated diapirs, while thin salt layers form rifts that are strongly asymmetric and rotated towards the direction of extension. Series II demonstrates that the number and dimensions of peripheral post-salt grabens, rollers, and reactive diapirs depends on the degree of coupling between sub- and supra-salt, which in turn is controlled by how the salt layer is distributed over active rift structures. Series III shows that deformation is compartmentalized into proximal, transitional, and distal domains which are characterized by extension, translation and contraction, respectively. The style and lateral extent of these domains however vary. In models where deformation is driven exclusively by tilting of the salt layer (S1) and open-toe salt advance, there is development of linear grabens cored by reactive-passive diapirs throughout most of the model length. This produces a more abrupt transition between the extensional and contractional domains and limited downdip salt inflation. In the pure-spreading model (S2), where deformation is driven solely by differential loading there is formation of a wide zone of salt inflation at the toe-of-slope and an overall greater number of contractional structures at the downdip end of the model, beyond the slope. In S3 there is development of a more variable suite of salt and overburden structures as typically observed along salt-bearing passive margins. In this model, deformation is characterized by the development of rollover and normal growth faults in the proximal domain that transition downdip onto upright diapirs associated with bowl-shaped minibasins, halokinetic sequences rotated and megaflaps. Our study improves our understanding of the extensional salt tectonic systems and the controls on different salt and post-salt geometries and kinematics.

Interpreting the nature of the Aulet and Adons diapirs from sedimentologic and stratigraphic analysis of flanking minibasin strata, Spanish Pyrenees, Catalunya, Spain

ABSTRACT The Aulet and Adons diapirs are exposures of Triassic Keuper evaporites in the Ribagorça Basin in the south-central Pyrenees. The diapirs have been alternatively interpreted from mapped structural relationships as either passive salt diapirs or extensional salt rollers. Correspondingly, the associated diapir-flanking minibasins have been interpreted as either salt-withdrawal or extensional-rollover minibasins, respectively. New field mapping, stratigraphic sections, petrographic analysis, correlation diagrams, and drone photography characterize the depositional facies and stratal architecture of the flanking Sopeira, Sant Gervàs, and Faiada minibasins (upper Albian to lower Santonian synrift to postrift strata), which in turn, constrains the origin and evolution of each salt body and associated minibasins. Each minibasin displays unique facies patterns and stratal thicknesses that reflect depositional systems evolving in response to spatially and temporally variable extension, salt evacuation, and passive diapirism during the Pyrenean rift and postrift phases. The Sopeira minibasin developed in the late Albian with significant localized subsidence, but it remains inconclusive if the bounding Aulet diapir originated as a passive diapir or a salt roller. The Llastarri fault zone, previously interpreted as a salt weld, separates the Sopeira minibasin from the primarily extensional Sant Gervàs minibasin, and is reinterpreted here as a remnant salt ridge, as it lacks evidence for passive diapirism. The Sant Gervàs minibasin remained relatively uplifted until the middle to late Cenomanian, along with the Faiada minibasin. Evidence for passive diapirism in the Faiada minibasin, including diapir-derived detritus and composite halokinetic sequences, indicate salt evacuation into the bounding Adons passive diapir. Integration of detailed sedimentologic and stratigraphic analyses with interpretations of basin formation and structural development provides better resolution of the earlier phases of gravity-driven extension and loading-driven salt movement of the Aulet and Adons diapirs; these insights help constrain structural interpretations and reconstructions of Pyrenean shortening and megaflap development in the Ribagorça Basin. Sedimentological and stratigraphic evidence for or against passive diapirism need to be integrated into structural interpretations, especially when precursor salt structures are obscured by subsequent contraction. This well constrained basin framework demonstrates the effects of inherited extensional structures and passive diapirism on Pyrenean shortening and megaflap rotation.

Burial wedges—Evidence for prolonged progressive burial of the Paradox Basin salt walls—With a detailed example from Gypsum Valley, Colorado

AbstractMany Paradox Basin passive salt diapirs underwent a prolonged history (>65 my) of progressive burial during the Early Triassic to Jurassic. Burial is recorded by a series of geographically limited wedge‐shaped stratal panels of diapiric roof, termed ‘burial wedges’, which partly covered the diapirs, thereby gradually narrowing them. Tectonostratigraphic analysis of the Triassic Chinle Fm. burial wedge developed on the Gypsum Valley diapir illustrates the typical features and processes associated with burial wedges. Burial wedges represent the first description of the geometry and deposition of strata deposited on a partially buried diapir. Recognition of burial wedges allows reinterpretation of Paradox Basin diapirs where large areas of the roof strata were syndepositionally folded rather than deformed in the Neogene. The observations and concepts can also be applied to the terminal histories of passive salt diapirs in other salt basins. Preserved burial wedges cover 97 km2, or 64% of the original Gypsum Valley diapir and overlie regional unconformities. Onlapping strata stack into wedge halokinetic sequences (HS). Caprock‐clast conglomerates indicate deposition on exposed diapirs. Syndepositional deformation of burial wedge strata formed small synclinal ‘microbasins’ and contractional chevron folds trending subparallel to the diapir margin. A four‐stage burial wedge model includes the following: (1) erosion of the diapir roof during formation of regional unconformities; (2) onlap and partial burial of the diapir; (3) local dissolution and possible concomitant gravity‐driven folding and (4) ongoing rotation during deposition, forming wedge HS signifying continued inflation of the top of the diapir. Post formation, the burial wedges were deformed in ways that obscure their original geometry. The most common deformation is downwarping of the burial wedge into the diapir due to dissolution or lateral movement of salt, creating an anticlinal fold that overlies the underlying diapir margin. These anticlines may be offset on small normal faults subparallel to the diapir margin. Burial wedges were faulted during later diapir breaching and solution collapse.

Evidence of halokinetic sequences in Albian deep carbonates around Triassic bodies in the ElKef-Tajerouine area, saliferous province of NW Tunisia

Evidence of halokinetic sequences in Albian deep carbonates around Triassic bodies in the ElKef-Tajerouine area, saliferous province of NW Tunisia

The transition from salt diapir to weld and thrust: Examples from the Northern Flinders Ranges in South Australia

AbstractThe interactions between salt diapirs, thrust welds and thrusts in contractional belts are poorly understood due to, first, the inability of seismic data to distinguish between thrusts and welds or resolve associated sub‐resolution deformation, and second, the paucity of good field examples. The Warraweena area in the Northern Flinders Ranges of South Australia contains examples of Neoproterozoic to Early Cambrian squeezed diapirs linked by steep reverse faults formed during the Delamerian Orogeny. Benefiting from good field exposures, we use geological mapping, cross‐section construction and conceptual structural models to assess the three‐dimensional geometry and evolution of the structures, the lateral transition from diapirs to linking faults and the variability of associated meso‐ and small‐scale deformation. Three discrete diapirs consist of narrow outcrops of Callanna Group megabreccia (Willouran in age) up to 5‐km long. Their diapiric origin is confirmed by local development of caprock, steepening of flanking strata in composite halokinetic sequences and reworked diapir and roof debris in adjacent strata. The surrounding rocks display only background levels of small‐scale deformation. In contrast, the linking faults show no evidence of precursor diapirism, have fault‐related anticlines up to 100s of m in wavelength in their hanging walls, and an associated increase in small‐scale deformation (i.e. millimetre to metre scale folds, fractures and shear fabrics). The transitions from diapirs to faults occur within less than 200 m as short thrust welds at the diapir terminations. The exposed structures are analogous to those found on the subsurface of other salt basins such as the Gulf of Mexico and the South Atlantic conjugate margins. The results of this work can aid geoscientists evaluating three‐way traps against squeezed diapirs, welds or faults, and can help them to predict the style and abundance of both halokinetic and small‐scale structures that are below seismic resolution.

Interactions between deep-water gravity flows and active salt tectonics

ABSTRACTBehavior of sediment gravity flows can be influenced by seafloor topography associated with salt structures; this can modify the depositional architecture of deep-water sedimentary systems. Typically, salt-influenced deep-water successions are poorly imaged in seismic reflection data, and exhumed systems are rare, hence the detailed sedimentology and stratigraphic architecture of these systems remains poorly understood.The exhumed Triassic (Keuper) Bakio and Guernica salt bodies in the Basque–Cantabrian Basin, Spain, were active during deep-water sedimentation. The salt diapirs grew reactively, then passively, during the Aptian–Albian, and are flanked by deep-water carbonate (Aptian–earliest Albian Urgonian Group) and siliciclastic (middle Albian–Cenomanian Black Flysch Group) successions. The study compares the depositional systems in two salt-influenced minibasins, confined (Sollube basin) and partially confined (Jata basin) by actively growing salt diapirs, comparable to salt-influenced minibasins in the subsurface. The presence of a well-exposed halokinetic sequence, with progressive rotation of bedding, beds that pinch out towards topography, soft-sediment deformation, variable paleocurrents, and intercalated debrites indicate that salt grew during deposition. Overall, the Black Flysch Group coarsens and thickens upwards in response to regional axial progradation, which is modulated by laterally derived debrites from halokinetic slopes. The variation in type and number of debrites in the Sollube and Jata basins indicates that the basins had different tectonostratigraphic histories despite their proximity. In the Sollube basin, the routing systems were confined between the two salt structures, eventually depositing amalgamated sandstones in the basin axis. Different facies and architectures are observed in the Jata basin due to partial confinement.Exposed minibasins are individualized, and facies vary both spatially and temporally in agreement with observations from subsurface salt-influenced basins. Salt-related, active topography and the degree of confinement are shown to be important modifiers of depositional systems, resulting in facies variability, remobilization of deposits, and channelization of flows. The findings are directly applicable to the exploration and development of subsurface energy reservoirs in salt basins globally, enabling better prediction of depositional architecture in areas where seismic imaging is challenging.

Passive versus active salt diapirism

Existing definitions for passive and active salt diapirism are somewhat overlapping and ambiguous. These terms are also equated to downbuilding and upbuilding, respectively, which are problematic concepts as originally conceived and even as subsequently modified. This results in conflicting usage and lack of consensus in the literature, creating confusion and decreasing the utility of the terms. For example, a diapir with a thin roof is defined as active by some but passive by others. In this short contribution, we first review historical definitions and then focus on several inherent problematic aspects including (1) the applicability of the concepts of downbuilding and upbuilding, (2) using the absence or presence and thickness of a diapir roof as criteria to classify diapirs as active or passive, and (3) the related concept of halokinetic sequences. We offer three suggestions in the hope of improving understanding and communication. First, we suggest that the terms downbuilding and upbuilding should be abandoned. Second, we argue that passive diapirism should be used sensu lato in that the presence or absence of a thin roof should not be the key defining factor. Third, we propose that active diapirism should be reserved for two specific scenarios: (1) uplift and folding of a thick roof during diapir rejuvenation and (2) the single brief stage when salt in a precursor structure (e.g., reactive diapir, salt-cored contractional fold, or salt pillow) breaks through its roof to subsequently rise as a passive diapir.

Hooked on salt: Rethinking Alpine tectonics in Hallstatt (Eastern Alps, Austria)

AbstractPermian salt in the Hallstatt and neighboring salt structures of the Eastern Alps (Austria) crops out along with Triassic deep-water deposits that are at odds with the surrounding Triassic platform carbonates. The traditional interpretation of this juxtaposition is that the salt bodies were emplaced in the Late Jurassic as gravity nappes onto the carbonate platforms, in what has been considered to be the earliest orogenic event in the Eastern Alps. Here we describe for the first time a world-class outcrop of halokinetic sequences in Triassic platform carbonates flanking the Hallstatt diapir. Combining this with other outcrop evidence, we prove that the Hallstatt diapir grew passively during the Triassic, surrounded by carbonate platforms, and extruded to the seabed during the Jurassic. The development of the Hallstatt diapir in a platform setting disproves its emplacement as a gravity-driven nappe, proves the relevance of salt tectonics in the Mesozoic development of the Eastern Alps, and challenges the existence of a Late Jurassic Alpine orogenic event.

Salt tectonics and controls on halokinetic-sequence development of an exposed deepwater diapir: The Bakio Diapir, Basque-Cantabrian Basin, Pyrenees

This work evaluates growth strata adjacent to the Bakio Diapir in the Basque Pyrenees, aiming to discuss the application of halokinetic-sequence concepts, mainly developed in shallow-water to subaerial environments, to deepwater depositional settings. This is one of the few exposed passive diapirs developed in deepwater environments, with both synkinematic carbonate and siliciclastic strata. Thus, considering that large hydrocarbon producing areas are located in salt provinces developed in deepwater environments, this study is of interest not only to researchers in salt tectonics, but also to industry geoscientists focusing on hydrocarbon exploration and production. We present a 3D analysis of this outstanding salt structure by integrating detailed geological cartography, high-resolution bathymetry, seismic, and well data. The resulting reconstruction enables us to trace the extent of the diapir offshore and decipher its evolution from its formation as a salt wall developed above the overlap of two basement-involved faults until its squeezing during the Pyrenean compression. But more significantly, it allows us to discern the roles played by bathymetry, subsidence, and sedimentation type in the configuration of halokinetic sequences developed in deepwater environments. Thus, our study shows that: 1) the geometry of halokinetic sequences is defined by the thickness of the roof edges, the dip of the salt-sediment interface in the limbs of the active drape fold, and the onlap angle of the synkinematic sediments over the salt; 2) the roof thickness is controlled not only by the ratio between salt-rise and regional sediment-accumulation rate, but also by the water depth of the diapir roof and the depositional environment that can promote vertical aggradation of a supra-diapir carbonate buildup; and 3) high surface slopes and consequent debrites are not exclusive to, and characteristic of, hook halokinetic sequences and tabular composite halokinetic sequences.

Contractional salt-tectonic system in the south Dezful embayment, Zagros

The Dezful embayment in Zagros has traditionally been interpreted as a typical fold belt with multiple detachment levels, including a lower detachment at the basement-cover interface and an upper detachment along the Miocene Gachsaran halite-bearing evaporites. This paper constrains diapiric processes in the Gachsaran detachment coeval with regional shortening that resulted in complex and hitherto unstudied salt structures and flanking synclinal minibasins. In this paper, well-tied seismic interpretation is integrated with field and remote-sensing mapping, cross-section construction, and stepwise tectono-sedimentary restoration. The results indicate that after the deposition of Mishan–lower Aghajari pre-kinematic overburden sediments, detachment folding initiated above the Gachsaran evaporites during late Tortonian times as a result of regional shortening. The salt-cored anticlines later actively pierced their roof to subsequently rise as passive diapirs and evolve into salt walls. Synclinal minibasins developed due to salt evacuation into flanking walls during the deposition of the Lahbari Mb. in Messinian–Pliocene. Remarkable sedimentary thickening and lateral shifts in minibasin depocenter towards the salt walls, accompanied by overturned collars and hook halokinetic sequences, are diagnostics of near-surface, syndepositional passive growth of diapirs during this stage. From Pliocene to recent, the major episode of regional shortening has squeezed these precursor salt walls to form thrust-welds. In conclusion, the well-exposed structures of south Dezful show an early shortening stage, then a transition to a combination of shortening and passive diapirism, and final thrusting along diapirs. This evolution model may be more common in other salt-influenced fold-thrust belts than is currently recognized.

The enigma of the Albian Gap: spatial variability and the competition between salt expulsion and extension

The Albian Gap is a uniquely large (up to 65 km wide and >450 km long), enigmatic salt-related structure in the Santos Basin, offshore Brazil. It is located near the basin margin and trends NE (i.e. subparallel to the Brazilian coastline). The gap is characterized by a near-complete absence of Albian strata above depleted Aptian salt. Its most remarkable feature is an equivalently large, equally enigmatic, basinward-dipping, supra-salt rollover that contains a post-Albian sedimentary succession that is up to 9 km thick. Owing to its unique geometry, size and counter-regional aspect, the origin and evolution of the Albian Gap has been the centre of debate for >25 years. This debate revolves around two competing models; that is, did it form as a result of thin-skinned (i.e. supra-salt) extension, or progradational loading and salt expulsion? The extension-driven model states that the Albian Gap (and overlying rollover) formed as a result of post-Albian gravity-driven extension accommodated by slip on a large, counter-regional, listric normal fault (the Cabo Frio Fault). Conversely, the expulsion-driven hypothesis states that the Albian Gap was established earlier, during the Albian, and that post-Albian deformation was controlled by differential loading, vertical subsidence and basinward salt expulsion in the absence of significant lateral extension. This study utilizes a large ( c . 76 000 km 2 ), dense (4–8 km line spacing), depth-migrated, 2D seismic dataset that fully covers and thus permits, for the first time, a detailed, quasi-3D structural analysis of the entire Albian Gap. In this study we focus on (1) the evolution of base-salt relief and the original salt thickness variations and (2) the geometry of the post-Albian rollover, and its related faults and salt structures. To constrain the kinematics of the Albian Gap, and how this relates to the evolution of the base-salt relief, we also apply novel structural restoration workflows that incorporate flexural isostasy, in addition to a detailed, sequential reconstruction of the intra-gap rollover sequences. Our results show that the geometry and kinematics of the Albian Gap vary along-strike, and that both post-Albian extension and expulsion play a significant role in its evolution. Basinward-dipping growth wedges, salt rollers and listric normal faults record extension, whereas sigmoidal wedges, halokinetic sequences and upturned near-diapir flaps, the latter two associated with large diapirs bounding the downdip edge of the gap, record basinward salt expulsion and inflation. Where the Albian Gap is relatively wide (>50 km), these processes alternate and operate at approximately equal proportions. Our results are consistent with the amount of basinward translation inferred from the analysis of ramp–syncline basins located downdip on the São Paulo Plateau. Our results seemingly reconcile one of the longest-running debates in salt tectonics, as well as having more general implications for understanding the regional kinematics and dynamics of salt-related structures in other salt basins, in particular the controls on the development of large, counter-regional faults. Supplementary material: Uninterpreted versions of the seismic sections are available at https://doi.org/10.6084/m9.figshare.c.5023088

Diapir kinematics in a multi-layer salt system from the eastern Persian Gulf

The eastern Persian Gulf hosts several salt structures sourced from two different evaporite layers, the Neoproterozoic-Cambrian Hormuz Salt and the Oligocene-Miocene Fars Salt. Based on seismic interpretation, we discuss the kinematics and dynamics of this autochthonous multi-layer salt system for three case studies: the Tunb and Hengam diapirs, and the Taftan salt anticline. Halokinetic sequences related to Hormuz salt evacuation suggest three main stages of evolution: i) onset of Hormuz Salt diapirism (Paleozoic), ii) diapir squeezing, and emplacement of allochthonous Hormuz Salt (Late Cretaceous to Oligocene-Miocene), and iii) development of secondary and tertiary salt welds (Upper Miocene). Since Fars Salt structures are absent in areas devoid of allochthonous Hormuz Salt, our structural model interprets that the driving mechanism for Fars Salt diapirism is directly related to the emplacement of allochthonous Hormuz Salt during the Zagros-Oman contractional event. The related halokinetic sequences suggest that the Fars Salt diapir kinematic style depends on to the timing of Hormuz Salt extrusion with regards to Fars Salt deposition. Our results provide new insight into the interaction between salt structures sourced from two distinct autochthonous salt layers.

Four‐dimensional Variability of Composite Halokinetic Sequences

AbstractThe architecture of salt diapir‐flank strata (i.e. halokinetic sequences) is controlled by the interplay between volumetric diapiric flux and sediment accumulation. Halokinetic sequences consist of unconformity‐bounded packages of thinned and folded strata formed by drape folding around passive diapirs. They are described by two end‐members: (a) hooks, which are characterized by narrow zones of folding (<200 m) and high taper angles (>70°); and (b) wedges, typified by broad zones of folding (300–1000 m) and low taper angles (<30°). Hooks and wedges stack to form tabular and tapered composite halokinetic sequences (CHS) respectively. CHSs were most thoroughly described from outcrop‐based studies that, although able to capture their high‐resolution facies variations, are limited in describing their 4D variability. This study integrates 3D seismic data from the Precaspian Basin and restorations to examine variations in CHS architecture through time and space along diapirs with variable plan‐form and cross‐sectional geometries. The diapirs consist of curvilinear walls that vary from upright to inclined and locally display well‐developed salt shoulders and/or laterally transition into rollers. CHS are highly variable in both time and space, even along a single diapir or minibasin. A single CHS can transition along a salt wall from tabular to tapered geometries. They can be downturned and exhibit rollover‐synclinal geometries with thickening towards the diapir above salt shoulders. Inclined walls present a greater proportion of tapered CHSs implying an overall greater ratio between sediment accumulation and salt‐rise relatively to vertical walls. In terms of vertical stacking, CHS can present a typical zonation with lower tapered, intermediate tabular and upper tapered CHSs, but also unique patterns where the lower sequences are tabular and transition upward to tapered CHS. The study demonstrates that CHSs are more variable than previously documented, indicating a complex interplay between volumetric salt rise, diapir‐flank geometry, sediment accumulation and roof dimensions.

Mass‐transport complexes (MTCs) document subsidence patterns in a northern Gulf of Mexico salt minibasin

AbstractMass‐transport complexes (MTCs) dominate the stratigraphic record of many salt‐influenced sedimentary basins. Commonly in such settings, halokinesis is invoked as a primary trigger for MTC emplacement, although the link between specific phases of salt movement, and related minibasin dynamics, remains unclear. Here, we use high‐quality 3D seismic reflection and well data to constrain the composition, geometry and distribution (in time and space) of six MTCs preserved in a salt‐confined, supra‐canopy minibasin in the northern Gulf of Mexico, and to assess how their emplacement relate to regional and local controls. We define three main tectono‐sedimentary phases in the development of the minibasin: (a) initial minibasin subsidence and passive diapirism, during which time deposition was dominated by relatively large‐volume MTCs (c. 25 km3) derived from the shelf‐edge or upper slope; (b) minibasin margin uplift and steepening, during which time small‐volume MTCs (c. 20 km3) derived from the shelf‐edge or upper slope were emplaced; and (c) active diapirism, during which time very small volume MTCs (c. 1 km3) were emplaced, locally derived from the diapir flanks or roofs. We present a generic model that emphasizes the dynamic nature of minibasin evolution, and how MTC emplacement relates to halokinetic sequence development. Although based on a single data‐rich case study, our model may be applicable to other MTC‐rich, salt‐influenced sedimentary basins.

Temporal evolution of the Darmadan salt diapir, eastern Fars region, Iran

A wide range of diapirs crop out along the eastern Fars region. They are constituted by the Pre-Cambrian to Early Cambrian Hormuz Fm. and located in the transition from the frontal structures of the Zagros fold-and-thrust belt and the Oman Ranges. While, in different previous works about the Persian Gulf, off-shore diapirs the deformation history has been determined on the basis of subsurface data, onshore evidence for salt tectonics activity is often limited to post-Oligocene stratigraphic units and is significantly overprinted by shortening. The Darmadan diapir is one of the few salt structures where is possible to observe halokinetic sequences involving the pre-collision Mesozoic succession in the Fars region of the Zagros fold-and-thrust belt. The objective of our study was to characterize on the base of field data, the stratigraphic and structural relationships between the Hormuz salt and its overburden in order to establish its temporal evolution. The Darmadan diapir is interpreted as a salt stock connected to a salt wall structure at depth evolving to a passive diapir, at least since Late Jurassic-Early Cretaceous times. Expansional geometries toward the diapir reveal that primary welding was already occurred at the Albian time. The onset of contractional deformation in the internal part of the Zagros and Oman orogenic systems is recorded by the reactivation of the Darmadan diapir during the Late Cretaceous. The Darmadan diapir continued to be exposed during the Paleogene and was squeezed during the Neogene to recent Zagros deformation. Second-order contractional features and related growth geometries constrain the timing of the secondary welding during the early stages of the late Miocene Darmadan anticline development. The explained structure remarks that the present structural trends of the Zagros fold-and-thrust belt in the eastern Fars region are the result of the reactivation of preexistent salt structures.