TS11.1

EDI
Salt and Shale Tectonics : Recent advances and challenges

This session is open to all recent works on salt-related tectonics, in various tectonic settings (extensional, contractional, strike-slip or simply gravitational, i.e. passive margins), areas of study (onshore or offshore), and types of approaches (subsurface or outcrop interpretation, seismic imaging and processing, numerical or analogue modelling, and rock-mechanics analysis). Likewise, we welcome contributions at various scales from the relationships between crustal-scale tectonics, evaporite deposition and salt tectonics within sedimentary basins and mountains, to the interaction between salt bodies and their surrounding sediments, to intra-salt deformation. Contributions on shale tectonics are also welcome.

Solicited presenters: Mark Rowan and Katherine Giles, Different scales of salt-sediment interaction around passive diapirs

Convener: Virginie Gaullier | Co-conveners: Gaia TravanECSECS, Bruno Vendeville
vPICO presentations
| Mon, 26 Apr, 11:00–12:30 (CEST)

Session assets

Session materials

vPICO presentations: Mon, 26 Apr

Chairpersons: Virginie Gaullier, Gaia Travan
11:00–11:05
11:05–11:15
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EGU21-14009
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solicited
Mark Rowan and Katherine Giles

Passive diapirism entails ongoing, near-surface syndepositional growth of a salt stock or wall. As such, the diapirs and intervening minibasins influence the development and geometries of associated sedimentary strata. In this short overview, we distinguish between two scales and aspects of salt-sediment interaction that reflect a depositional continuum from the topographic highs of diapir roofs to the lows of depocenters. At the larger, multi-km scale, minibasin tectonostratigraphic successions form bowls, troughs, wedges, or layers that respond to differential evacuation of the deep salt layer. These successions have internal concordant, onlapping, or truncated geometries, and they stack into different patterns based on the evolution of active salt tectonic processes. At the smaller scale, passive diapirs create local sea-floor scarps due to drape folding of the diapir roof over the edge of the rising diapir. Depending primarily on the thickness of the roof, this results in tabular or tapered composite halokinetic sequences within 1 km or less of the diapir edge. It is important to keep these geometries and processes separate as they have distinct implications for sediment transport and deposition as well as the definition and detailed geometries of hydrocarbon traps in three-way truncations against diapirs and welds.

How to cite: Rowan, M. and Giles, K.: Different scales of salt-sediment interaction around passive diapirs, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14009, https://doi.org/10.5194/egusphere-egu21-14009, 2021.

11:15–11:17
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EGU21-14873
Prokop Závada, Jiří Bruthans, Sadegh Adineh, Michael Warsitzka, and Mohammad Zare

The Zagros fold-and-thrust belt in Southern Iran is famous for its spectacular outcrops of salt diapirs. Most of these diapirs already existed prior to the onset of the Zagros orogeny, but tectonic shortening caused their reactivation and extrusion of the salt. Thus, the diapir exposures often provide access to intense internal deformation of the Hormuz salt series and its entrained interlayers. However, highly soluble evaporites (mainly halite) were already dissolved in many of the exposures leaving behind degraded ‘caprock’, which is built of a multi-compositional residuum of less soluble minerals and rocks. Based on geological field studies on two iconic salt diapirs in Southern Iran, the Karmostaj (Gach) and the Siah Taq diapir, we ascertained that the caprock is also intensively deformed. The accessible part of the caprock is roughly 200 m thick and consists of a fine-grained, laminated gypsum containing fragments of brecciated carbonates and siliciclastics.  Especially in the down- and mid-slope regions of the salt exposure, this mixture is sheared and folded, but also dissected by thrust faults. Since such deformation processes in the caprock were not described before, there is a lack in explanations for the timing, the depth of formation and the structural evolution of these structures. For instance, it is unclear if the ductile shearing of the relatively competent gypsum matrix and the brecciation of the clasts took place near the surface or in larger depths (a few hundreds of meters), where confining pressure is higher.

In this study, we want to classify the observed structures in the caprock, characterize deformation mechanisms and differentiate typical deformation domains. Based on that, we speculate about the timing and structural evolution of the caprock deformation and suggest that three scenarios can be imagined: (1) Pre-extrusion deformation: The caprock exposed today was buried by a thicker caprock package and, therefore, is compacted and mechanically strong.  With the onset of the Zagros orogeny, tectonic shortening of the buried diapir caused lateral deformation before the salt extrusion. (2) Syn-extrusion deformation: The caprock is relatively young and was mechanically weak after its formation. Thus, it was deformed during diapir extrusion and, then, solidified during degradation of the salt. (3) Post-extrusion deformation: The caprock was mainly formed after salt extrusion, but it remained relatively immobile. The caprock matrix is occasionally weakened by the infiltration of meteoric water, and continued to be deformed due to gravitational gliding even after the dissolution of the rock salt.  In order to test these hypotheses, we intend to carry out analogue experiments in which we try to model a squeezed diapir. In a parameter study, the thickness and the material of the covering layer simulating the caprock will be varied to assess possible differences in the deformation patterns.

How to cite: Závada, P., Bruthans, J., Adineh, S., Warsitzka, M., and Zare, M.: Intense deformation of the caprock on salt extrusions in the Iranian Zagros Mountains – Insights from geological mapping and analogue modeling, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14873, https://doi.org/10.5194/egusphere-egu21-14873, 2021.

11:17–11:19
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EGU21-3233
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ECS
Vincent Wicker and Mary Ford

Detailed structural and stratigraphic field mapping is used to reconstruct the Jurassic to Late Cretaceous diapiric and tectonic evolution of the Toulon Fault Zone, eastern Beausset Syncline and Toulon Belt, southern France, which represents the easternmost vestige of the Pyrenean orogen in Provence. This complex salt-rich area records a complete history from Jurassic-early Cretaceous subsidence and Aptian-Albian oblique rifting to Late Cretaceous Pyrenean-Provençal shortening. Halokinetic sequences and geometries were preserved principally on the northern flank of the Mont Caume salt diapir sourced from the Upper Triassic Keuper unit. Our field observations are best explained by a model where halokinetic activity interacted with regional deviatoric stresses from early-Jurassic to Santonian/Campanian times. Halokinetic wedges of Jurassic and Early Cretaceous carbonates thin toward the diapir, recording early salt mobilisation. Inverted relics of Apto-Albian rift depocenters are aligned along the northern margin of the Toulon Belt and the adjacent Bandol belt that lies to the west.  The Turonian-Coniacian Revest depocenter developed due to localized strong asymmetrical growth of the Mont Caume diapir. The three-dimensional form and growth of the diapir controlled lateral migration of the Revest depocenter, thickness variations, progressive unconformities, and the westward increase in stratal overturning of a flap. A component of N-S compression with related accelerated halokinetic activity can explain our observations and can be considered as the earliest expression of N-S convergence in the Provencal fold belt.  Further west, the overturned Beausset klippe can be interpreted as the remnant of a megaflap on the northern flank of the Bandol diapir. The Toulon belt salt structures are excellent field analogues to others observed in the external Alps and Pyrenees.

How to cite: Wicker, V. and Ford, M.: Mesozoic salt tectonics in the Toulon Belt, Eastern Provence : Inversion of a salt-rich fault zone, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3233, https://doi.org/10.5194/egusphere-egu21-3233, 2021.

11:19–11:21
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EGU21-15420
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ECS
Alexandre Hamon, Caroline Mehl, Damien Huyghe, Sidonie Révillon, and Jean-Paul Callot

The external Alps record a whole Wilson cycle that began at early Mesozoïc times by an extensional phase leading to the deposition of thick marine deposits upon an upper Triassic basement including a thick salt layer. Several diapiric structures (e.g. Astoin, the Barre de Chine ; Célini et al., 2020) are the witnesses of this important salt activity during deposition and the subsequent deformation through the Lower Jurassic. Otherwise, Triassic salt allowed thrusting on several decollement levels and emplacement of major thrusted units, such as the “Nappe de Digne” or the Authon thrust sheet, during the alpine phase s.s, initiated at the Oligocene-Miocene boundary. Between these two periods, the external Alps story is more uncertain and none salt activity has been clearly demonstrated except westwards in the Vocontian basin. In the whole South-East basin, only few clues, as bipyramidal quartz found in Priabonian deposits in the western Baronnies suggest a potential salt activity at surface during the Paleogene. However, in the St-Geniez areas, some Oligocene sediments, located at the vicinity of salt structures suggest a potential diapiric growth during this period. Indeed, some stratigraphic gypsum beds are found in an Oligocene lacustrine series, directly thrusted by the Authon thrust sheet.  None evaporite environments are described in the whole region at Oligocene times, which suggest a possible recycling of Triassic evaporites.

In order to determine if theses deposits are related to a Paleogene salt activity, a multi-analytical approach was used. First, a field study allowed characterizing the facies and the sedimentary filling and defining the stress regime during the deposit, by kinematic inversion on fractures which indicates a constant N-S compression during the Oligocene. The presence of halophilic fauna at the base of the lacustrine series of the St-Geniez area attests for saline influences during deposit. Moreover, 4km to the SW, a wedge in the conglomerates of the alpine continental molasse (so called red molasse) resting directly on Sorine’s Triassic diapir was put forward. Cargneules and dolomites from the Triassic constitute an important part of the reworked material. These observations indicate that the Sorine's diapir was active during the deposition of the Oligocene series. Then, a precise chemostratigraphic framework was determined by use of δ13C and δ18O isotopic data on the lacustrine limestones. 87Sr/86Sr isotopic ratio on gypsum beds of the lacustrine series aimed at determining their ages and a possible Triassic evaporite sourcing. Our results gave an age ranging from 6 to 23 Ma, which does not correspond with the Oligocene age of the overlying and underlying sediments. Moreover, the large variation in isotope ratios suggests that this gypsum did not come from primary precipitation but from leaching of a pre-existing evaporite source. In conclusion, field observations, together with geochemical analyses, made it possible to highlight the relationships between tectonics, salt tectonics and sedimentation and also to reconstruct the paleogeography of the region at the end of the Paleogene.

 

References

Célini, N., Callot, J.P., Ringenbach, J.C., Graham, R. (2020,). Jurassic salt tectonics in the SW sub-Alpine fold and thrust belt. Tectonics

 

How to cite: Hamon, A., Mehl, C., Huyghe, D., Révillon, S., and Callot, J.-P.: Salt activity and diapirism during the Paleogene in the Baronnies Orientales (South-East basin, France) : paleogeographic and structural implications., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15420, https://doi.org/10.5194/egusphere-egu21-15420, 2021.

11:21–11:23
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EGU21-15572
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ECS
Michael Stanley Dale, Ismael Falcon-Suarez, and Hector Marín-Moreno

Dissolution of halite rock can significantly impact underground constructions (e.g., caverns for energy storage and abandoned caverns) and above ground constructions (e.g., highways and buildings) potentially causing a threat to human life from land subsidence and sinkhole hazards, instability to underground construction and pollutant release. In this work, we explore and quantify changes in elastic and hydromechanical properties during dissolution of halite rock by migration of water.

We evaluated the impact of dissolution on the geophysical properties of pristine (non-fractured) and fractured halite samples (with ~2.7% dolomite), using a synthetic (seawater-like) brine solution (3.5wt% NaCl). The dissolution test commenced by setting an initial effective pressure of 15 MPa (with minimum pore pressure of 0.1 MPa), equivalent to a depth of ~720 m below ground level. This confining pressure of 14.9 MPa ensured the adequate contact between sample and the ultrasonic instrumentation (P- and S-wave sensors), and the set of electrodes for electrical resistivity. The test procedure was set to investigate the effect of increasing pore pressure from 0.1 to 14 MPa on dissolution. This procedure was only successful for the non-fractured sample, as dissolution rapidly occurred in the fractured sample during the initial stage of the test.

The non-fractured halite shows that P-wave velocity increases with increasing inlet pore pressure initially, followed by a lower pore fluid sensitivity stage. After this stage, the P-wave and the Vp/Vs ratio reduce and then ultrasonic velocities tend to their original values when effective pressure tends to zero. These results suggest that capillary pressure effects are initially increasing the bulk properties of the rock by filling the micro-pores, while dissolution is occurring locally, nearby the inlet-flow port, and therefore invisible to our geophysical tools. The small porosity fraction of 1.1% allows the saturating fluid to rapidly equilibrate with the surrounding halite within the pores, slowing down the dissolution process. In a close halite system with a local and continuous brine supply source, local dissolution may allow pressure increase up to the overburden stress and affect the geomechanical integrity of the reservoir by a combined fracturing-dissolution process.

How to cite: Dale, M. S., Falcon-Suarez, I., and Marín-Moreno, H.: Geophysical response to dissolution of undisturbed and fractured evaporite rock during brine flow, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15572, https://doi.org/10.5194/egusphere-egu21-15572, 2021.

11:23–11:25
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EGU21-3240
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ECS
Pablo Granado, Pablo Santolaria, Elizabeth Wilson, Oriol Ferrer, and Josep Anton Muñoz

Salt and related structures have a strong influence on the formation of extensional basins during lithospheric stretching and thermal subsidence at rifted margins. Salt significantly influences as well the structural styles and kinematics of fold-and-thrust belts. We aim to characterize the structure of inverted minibasins and salt-influenced fold-and-thrust belts, but the challenge is to understand, and to match, the present day contractional structures with reasonable pre-orogenic configurations. Yet, we still lack proper understanding on the development of these salt-sediment systems and particularly, how salt tectonics is initially triggered and evolves through space and time. Two fundamental triggering mechanisms on rift to passive margin salt tectonics are known: (1) extension by gravitational collapse, and (2) differential loading. Key questions are: do these mechanisms occur at the same time or does one commonly follow the other? Which one is first and which one dominates? Does it depend on the location and timing of deformation on the passive margin? Which are the stratigraphic evidences and structural geometries that may help us to answer these questions? Recognizing the initial structural geometries of these minibasins once they have been incorporated into a fold and thrust belt is challenging but of paramount importance.

In this contribution we address some of these questions by showing a brief historical review of concepts and show end-member analogue models of fold-and-thrust belts developed from the inversion and incorporation of rift to passive margin salt basins. Our work is inspired by field observations from the Pyrenees and the Northern Calcareous Alps, as well as from present day continental margins.

How to cite: Granado, P., Santolaria, P., Wilson, E., Ferrer, O., and Muñoz, J. A.: SALT: from rifted margins to fold-and-thrust belts. Insights from analogue modelling and case studies, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3240, https://doi.org/10.5194/egusphere-egu21-3240, 2021.

11:25–11:27
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EGU21-4659
Michael Warsitzka, Prokop Závada, Fabian Jähne-Klingberg, and Piotr Krzywiec

Salt flow in rift basins is mainly driven by sub- and supra-salt extension imposing shear stresses and differential loading on the salt layer. In many rift basins, the graben flanks are tilted as a result of thermal subsidence and sediment load. Such tilt induces additional basin-ward directed stresses potentially causing downward directed salt flow and gravity gliding of the supra-salt overburden. However, sediment loading in extensional basins is usually largest in the basin centre, which would lead to an upward directed salt expulsion and might act as an effective buttress resisting downward gliding.

Our aim is to investigate the opposing influence of sub-salt extension, sedimentary loading and tilting on deformation patterns in the viscous salt and the brittle overburden. We try to assess under which geological configurations (e.g. minimum basin slope or topographic gradient) upward directed salt flow and downward directed gravity gliding are the dominating deformation processes in extensional basins. Therefore, we developed a new analogue modelling apparatus enabling to simulate the processes of tectonic extension of a graben structure and the gradual tilting of the graben flanks, acting either simultaneously or separately. Using digital image correlation technique, temporal and spatial changes of the displacement and strain patterns can be analysed. Cross sections through the final experiments enable to identify structures characteristic for specific driving processes.

Here, we present results of a preliminary experimental study in which the basic influence of flank tilting and syn-kinematic sedimentation on salt tectonics in rift basins is examined. In case that the graben flanks remain flat during extension, widespread extensional fault zones develop on the footwall sides near the graben faults. In case that the flanks are tilted simultaneously with basal extension, additional extensional fault zones evolve at the upslope basin margins resulting from downward gliding of the overburden. In the downslope basin centre, this peripheral extension is balanced by reduced amounts of extension near the graben and later by shortening above the graben bounding faults and the hanging wall graben centre. If syn-kinematic sedimentation is introduced, downslope gravity gliding is significantly reduced and extensional fault zones are rather localized. Peripheral extensional structures observed in the experiments resemble typical thin-skinned extensional structures occurring at the flanks of many salt-bearing rift basins, e.g. the Polish Basin and Norwegian-Danish Basin. Thus, such structures might serve as diagnostic indicators for the occurrence of gravity gliding in rift basins.

How to cite: Warsitzka, M., Závada, P., Jähne-Klingberg, F., and Krzywiec, P.: A new experimental approach to assess the influence of gravity gliding on salt tectonics in rift basins, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4659, https://doi.org/10.5194/egusphere-egu21-4659, 2021.

11:27–11:29
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EGU21-12519
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ECS
Sian Evans, Christopher Jackson, Sylvie Schueller, and Jean-Marie Mengus

Salt flows like a fluid over geological timescales and introduces significant structural complexity to the basins in which it is deposited. Salt typically flows seaward due to tilting of the basin margins, and is therefore influenced by the geometry of the surface that it flows across (e.g. fault scarps or folds on the base-salt surface). This can lead to coupling of sub- and supra-salt structures, with the orientation and distribution of base-salt structures reflected in the structure of the overburden. However, precisely what controls the degree of strain coupling during salt-detached translation is still poorly understood, in particular the role played by salt thickness and lithological heterogeneity. This partly reflects the fact that it can be difficult to deconvolve the relative contributions of natural variables such as the magnitude of relief, sediment supply, and regional tectonic regime. In addition, seismic data provide only the present structural configuration of salt basins, from which their formative kinematics must be inferred. If we can develop a better understanding of how sub-salt structure controls the types and patterns of supra-salt deformation, we can produce better kinematic (structural) restorations of salt basins and, therefore, have a better understanding of the related mechanics.

In order to isolate the influence of salt thickness and heterogeneity on sub- to supra-salt strain coupling during salt-detached horizontal translation, we present a series of physical analogue models with controlled boundary conditions. We use a simple base-salt geometry comprising three oblique base-salt steps, and vary the thickness and composition of the ductile salt analogue in each experiment. X-ray tomography allows us to image the internal structure during model evolution and therefore gain a 4D picture of its structural development.

Results show that thicker and more homogeneous salt units experience more vertical movement (i.e. minibasin subsidence and diapiric rise) and the overburden structure is less explicitly coupled with the underlying base-salt relief. Conversely, thinner and more heterogeneous salt units restrict vertical movement, and therefore the resulting overburden structure is dominated by lateral movement and more closely coupled to the geometry of the base-salt surface. These results highlight the important role of base-salt relief in the subsequent structural evolution of salt basins and why, despite broad similarities between different salt basins, there is significant variability in their structural styles.

How to cite: Evans, S., Jackson, C., Schueller, S., and Mengus, J.-M.: Salt thickness and heterogeneity control the degree of coupling between sub- and supra-salt structure during salt-detached translation: evidence from physical models, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12519, https://doi.org/10.5194/egusphere-egu21-12519, 2021.

11:29–11:31
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EGU21-3263
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ECS
Francyne B. Amarante, Christopher A-L. Jackson, Leonardo M. Pichel, Claiton M. S. Scherer, and Juliano Kuchle

Salt-bearing passive margin basins offshore SE Brazil have been and remain attractive for hydrocarbon exploration and production. In the Campos Basin, major reservoir types include post-salt turbidites, which are located in structural traps related to thin-skinned faulting above salt anticlines and rollers. Classic models of gravity-driven salt tectonics commonly depict kinematically linked zones of deformation, characterised by updip extension and downdip contraction, separated by a weakly deformed zone associated with downdip translation above a relatively smooth base-salt surface. We use 2D and 3D seismic reflection and borehole data from the south-central Campos Basin to show that this does not adequately capture the styles of salt-detached gravity-driven deformation above relict, rift-related relief. The base-salt surface is composed of elongated, broadly seaward-dipping ramps with structural relief reaching c. 2 km. These ramps define the boundary between the External High and the External Low, basement structures related to the rift tectonics. Local deformation associated with the base-salt ramps can overprint and/or influence regional, margin-scale patterns of deformation producing kinematically-variable and multiphase salt deformation. We define three domains of thin-skinned deformation: an updip extensional domain, subdivided into subdomains E1 and E2, an intermediate multiphase domain and a downdip contractional domain. The multiphase domain is composed of three types of salt structures with a hybrid extensional-contractional origin and evolution. These are: (i) contractional anticlines that were subjected to later extension and normal faulting; (ii) diapirs with passive and active growth later subjected to regional extension, developing landward-dipping normal faults on the landward flank; and, lastly, (iii) an extensional diapir that was subsequently squeezed. We argue that this multiphase style of deformation occurs as a consequence of base-salt geometry and relief creating local variations of salt flow that localize extension at the top and along the ramps, and contraction at the base. Translation and extension of salt and its overburden across major base-salt ramps resulted in three ramp syncline basins northeast of the study area, partially bounded by salt-detached listric faults. The temporal and spatial distribution and evolution of these and other key salt and overburden structures, and their relationship to base-salt relief, suggest 30 to 60 km of horizontal gravity-driven translation of salt and overburden.

How to cite: B. Amarante, F., A-L. Jackson, C., M. Pichel, L., M. S. Scherer, C., and Kuchle, J.: Pre-salt rift morphology controls salt tectonics in the Campos Basin, offshore SE Brazil, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3263, https://doi.org/10.5194/egusphere-egu21-3263, 2021.

11:31–11:33
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EGU21-4711
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ECS
Aurio Erdi and Christopher Jackson

Strike slip faults are a prominent tectonic feature in Earth to accommodate horizontal and/or oblique slip that trend parallel to fault strike. These faults are commonly formed on plate boundaries setting, where they are basement-involved and driven by elastic crustal loading at seismogenic depths. Still, we also observe the strike slip faults on salt-bearing slopes, where the faults are typically thin-skinned and accommodate spatial variability in the rate of seaward flow of salt and its overburden. In both cases, relatively little is still known of their three-dimensional geometry and growth in comparison to both normal and reverse fault, that have been extensively studied.

We use a high-quality, depth-migrated 3D seismic dataset to investigate salt-detached strike-slip faults in the mid-slope translational domain of the Outer Kwanza Basin, offshore Angola. We show that NE-SW-striking faults are presently located above elongate, margin-parallel, NE-trending ramps, more amorphous, dome-like structural highs, and areas of relatively subdued relief. The faults are broadly planar, display normal and/or reverse offsets, and may locally bound negative flower structures. These faults offset a range of salt and overburden structures, including salt walls and anticlines, and salt -detached thrusts and normal faults, defining six major structural compartments. Our displacement-distance (Tx) analysis of several faults reveal they are characterized by complex throw distributions that define 3-to-10, now hard-linked segments. In vertical profiles, these segments are characterized by symmetric-to-asymmetric throw distributions (Tz) that record throw maxima at the top of the Albian, Eocene and/or Early Miocene. Expansion indices (EI) and isopach maps demonstrate the presence of fault-related growth strata, with complex thickness patterns also reflecting the combined effect of vertical (i.e. diapirism) and horizontal (i.e. translation) salt tectonics.  Taken together, our observations suggest the salt detached strike-slip faults evolved during three key phases: (i) Albian – nucleation and local linkage of individual segments; (ii) Eocene-to-Oligocene – reactivation, propagation, and death of many now-linked segments; and (iii) Miocene – local fault reactivation due to salt diapirism.  

We show that salt detached strike-slip faults in the translational domain of the Outer Kwanza Basin grew above either rugose or relatively flat base-salt surface. More specifically, salt detached strike-slip faults, like normal and reverse faults documented elsewhere, grew in response to the propagation and eventual linkage of initially isolated segments. We also highlight that the coeval growth of salt walls can play a role in controlling the three-dimensional geometry and kinematics of salt detached strike-slip faults.

How to cite: Erdi, A. and Jackson, C.: Three-dimensional geometry and growth of salt-detached strike-slip faults, Outer Kwanza Basin, offshore Angola, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4711, https://doi.org/10.5194/egusphere-egu21-4711, 2021.

11:33–11:35
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EGU21-8999
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ECS
Chibuike Nnadi and Alexander Peace

Abstract

The North Sea is a complex rift system that has undergone a polyphase evolutionary history from the Palaeozoic to Recent, including the deposition, and subsequent mobilisation of Upper Permian Zechstein salt. This halokinesis has played an integral role in the geologic evolution of the North Sea, controlling the present-day structural style. The driving mechanisms and kinematics of salt deformation have gained widespread interest partly due to the potential role of salt in hydrocarbon systems, and also due to its potential uses for nuclear waste disposal. However, the primary driving mechanism for salt-related deformation in the North Sea is debated. Here, we focus on the Mid-North Sea High (MNSH), an area of the North Sea in which salt-related deformation is widespread. We interpret open access data made available by United Kingdom Oil and Gas Authority (OGA) including 2D seismic reflection, gravity, magnetic and well data in Petrel, followed by forward modeling and restoration in the MOVE software. The results show that, the style of salt-related deformation in the MNSH region is highly variable, with the influence of local stratigraphy, as well as basement structures, also contributing to the deformation style.

Keywords: Salt tectonics, Halokinesis, North Sea, Mid North Sea High

How to cite: Nnadi, C. and Peace, A.: Reconstruction of Salt Tectonics: Insights from the Mid North Sea High, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8999, https://doi.org/10.5194/egusphere-egu21-8999, 2021.

11:35–11:37
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EGU21-13593
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ECS
Wajdi Belkhiria, Haifa Boussiga, Imen Hamdi Nasr, Adnen Amiri, and Mohamed Hédi Inoubli

The Sahel basin in eastern Tunisia has been subject for hydrocarbon exploration since the early fifties. Despite the presence of a working petroleum system in the area, most of the drilled wells were dry or encountered oil shows that failed to give commercial flow rates. A better understanding of the tectono-sedimentary evolution of the Sahel basin is of great importance for future hydrocarbon prospectivity. In this contribution, we present integration of 2D seismic reflection profiles, exploration wells and new acquired gravity data. These subsurface data reveal that the Sahel basin developed as a passive margin during Jurassic-Early Cretaceous times and was later inverted during the Cenozoic Alpine orogeny. The occurrence of Triassic age evaporites and shales deposited during the Pangea breakup played a fundamental role in the structural style and tectono-sedimentary evolution of the study area. Seismic and gravity data revealed jointly important deep-seated extensional faults, almost along E-W and few along NNE–SSW and NW-SE directions, delimiting horsts and grabens structures. These syn-rift extensional faults controlled deposition, facies distribution and thicknesses of the Jurassic and Early cretaceous series. Most of these inherited deep-seated normal and transform faults are ornamented by different types of salt-related structures. The first phase of salt rising was initiated mainly along these syn-extensional faults in the Late Jurassic forming salt domes and continued into the Early and Late Cretaceous leading to salt-related diapir structures. During this period, the salt diapirism was accompanied by the development of salt withdrawal minibasins, characterized important growth strata due the differential subsidence. These areas represent important immediate kitchen areas to the salt-related structures. The later Late Cretaceous - Cenozoic shortening phases induced preferential rejuvenation of the diapiric structures and led to the inversion of former graben/half-graben structures and ultimately to vertical salt welds along salt ridges. These salt structures represent key elements that remains largely undrilled in the Sahel basin. Our results improve the understanding of salt growth in eastern Tunisia and consequently greatly impact the hydrocarbon prospectivity in the area.

How to cite: Belkhiria, W., Boussiga, H., Hamdi Nasr, I., Amiri, A., and Inoubli, M. H.: Interplay between tectonic inheritance and salt tectonics in the tectono-sedimentary evolution of the Sahel basin (eastern Tunisia): implications for hydrocarbon prospectivity, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13593, https://doi.org/10.5194/egusphere-egu21-13593, 2021.

11:37–11:39
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EGU21-4182
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ECS
Massimo Bellucci, Daniel Aslanian, Maryline Moulin, Marina Rabineau, Estelle Leroux, Romain Pellen, Jeffrey Poort, Anna Del Ben, Christian Gorini, and Angelo Camerlenghi

Salt tectonics at salt-bearing margins is often interpreted as the combination of gravity spreading and gravity gliding, mainly driven by differential sedimentary loading and margin tilting, respectively. Nevertheless, in the Western Mediterranean Sea, the classical salt tectonics models are incoherent with its morpho-structural setting: the Messinian salt was deposited in a closed system, formed several Ma before the deposition, horizontally in the entire deep basins, above a homogenous multi-kilometre pre-Messinian thickness. The subsidence is purely vertical in the deep basin, implying a regional constant initial salt thickness, the post-salt overburden is homogenous and the distal salt deformation occurred before the mid-lower slope normal faults activation. Instead, the compilation of MCS and wide-angle seismic data highlighted a clear coincidence between crustal segmentation and salt morphology domains. The geometrical variation of salt structures seems to be related to the underlying crustal nature segmentation. Regional thermal anomalies and/or fluid escapes, associated with the exhumation phase, or the mantle heat segmentation, could therefore play a role in adding a further component on the already known salt tectonics mechanisms. The compilation of crustal segmentation and salt morphologies in different salt-bearing margins, such as the Santos, Angolan, Gulf of Mexico and Morocco-Nova Scotia margins, seems to depict the same coincidence. In view of what is observed in Western Mediterranean Sea, the heat segmentation influence in the passive margins should not be overlooked and deserves further investigation.

How to cite: Bellucci, M., Aslanian, D., Moulin, M., Rabineau, M., Leroux, E., Pellen, R., Poort, J., Del Ben, A., Gorini, C., and Camerlenghi, A.: Salt morphologies and crustal segmentation relationship: new insights from Western Mediterranean Sea and other salt passive margins , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4182, https://doi.org/10.5194/egusphere-egu21-4182, 2021.

11:39–11:41
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EGU21-16548
Virginie Gaullier, Gaël Lymer, Bruno Vendeville, and Frank Chanier

The METYSS project (Messinian Event in the Tyrrhenian from Seismic Study) is based on high-resolution seismic data acquired along the Eastern Sardinian margin. The main aim is to study the Messinian Salinity Crisis (MSC) in the Western Tyrrhenian Basin, but we also investigated the thinning processes of the continental crust and the timing of crustal vertical movements across this backarc domain. Our first results shown that rifting ended before the MSC, but that crustal activity persisted long after the end of the rifting. This has been particularly observed on the proximal margin, the East-Sardinia Basin, where the Mobile Unit (MU, mobile Messinian salt) is thin or absent. In this study, we examined the distal margin, the Cornaglia Terrace, where the MU accumulated during the MSC and acted as a décollement, thus potentially decoupling the basement from the sedimentary cover. Our observations provide evidence for lateral flow and gravity gliding of the salt and its brittle sedimentary overburden along local basement slopes generated by the post-MSC tilting of some basement blocks formerly generated during the rifting. We also investigated an intriguing wedge-shaped body of MU located in a narrow N-S half graben bounded to the west by a major, east-dipping, crustal normal fault. Classically, one could think that this salt wedge is related to the syn-tectonics deposition of the MU, but we propose an original scenario, in which the post-rift vertical motion of the major fault has been cushioned by lateral flow of an initially tabular salt layer, leaving the supra-salt series apparently unaffected by the crustal motions of the basement. We tested this scenario by comparing natural data and physical (analogue) modelling data. Our results reveal that salt tectonics provides a powerful tool to understand the deep crustal tectonics of the margin and to constrain the timing of vertical motions in the Western Tyrrhenian Basin, results that can be applied to rifted salt-bearing margins worldwide.

How to cite: Gaullier, V., Lymer, G., Vendeville, B., and Chanier, F.: Interactions between salt tectonics and crustal tectonics on the Eastern Sardinian Margin (Western Tyrrhenian Sea), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16548, https://doi.org/10.5194/egusphere-egu21-16548, 2021.

11:41–11:43
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EGU21-9640
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ECS
Simon Blondel, Angelo Camerlenghi, Anna Del Ben, and Massimo Bellucci

This study presents the interpretation of reprocessed seismic data covering the southwestern Balearic promontory and the central Algerian basin. The new depth processing of 2D seismic lines dataset allows for the first time a good resolution on salt structures in the deep basin. Most of the salt structures result from active diapirism. In the deep basin, sedimentary loads and regional shortening are proposed to be the dominant driving forces, showing an overall contractional salt system. The north Algerian margin tectonic reactivation could have provoked a regional shortening of the salt structures and overburden. Identified unconformities suggest that this process probably started shortly after salt deposition and is still active nowadays. It is expressed by salt sheets, pinched diapirs and a décollement level. The African convergence and the narrowness of the western Algerian basin could be the explanation of an overall greater salt deformation intensity compared to the eastern Algerian basin. This demonstrates how in tectonic and sedimentary components appear to be dominant in salt deformation in the central Algerian basin compared to gravitational gliding, only localized in the proximal parts of the margin.

How to cite: Blondel, S., Camerlenghi, A., Del Ben, A., and Bellucci, M.: Late Miocene to present-day tectonostratigraphy of the northern central Algerian Basin: Evidence of a contractional salt system from reprocessed seismic data, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9640, https://doi.org/10.5194/egusphere-egu21-9640, 2021.

11:43–11:45
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EGU21-11948
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ECS
Gaia Travan, Virginie Gaullier, Bruno Vendeville, Jacques Déverchère, Fadl Raad, and Johanna Lofi

The Algerian margin, located in the Western Mediterranean basin, is reactivated in compression since 8 My due to the convergence between Africa and Eurasia, and is nowadays subjected to a N45W compression of several mm/y (Jolivet et al., 1995; Noquet et Calais, 2004). While the reactivation is attested by GPS measurements and destructive seismic events, such as the earthquake of Boumerdes in 2003 (M 6.8), the visualization in the seismic data of the deep structures is made difficult by the presence of a thick Messinian salt layer. The seismic reflection profiles acquired on the Algerian margin during the “Maradja I” oceanographic survey (2003) highlighted the presence of north-verging thrusts offshore Algiers (Déverchère et al., 2005; Domzig et al., 2006), as well as the peculiar geometry of the Messinian salt layer (Lofi et al., 2011, Obone Zue Obame, 2011).

Between 2 and 4° East, the margin presents particularly complex salt structures, partly associated to the uplift of the plateau as a consequence of the crustal convergence (Déverchère et al., 2005; Domzig et al., 2006). One of the consequences of the uplift of the plateau is the dipping of the base salt horizon towards W to NNW. Moreover, from the analysis of the seismic reflection profiles, the presence of early (syn-UU) salt movement in the profiles parallel to the margin is clear, while the profiles perpendicular to the margin show compressional features mostly active during the Pliocene to Quaternary period.

From the observation of the natural example, and from the comparison with different analogue models, we conclude that offshore Algiers we find the major salt structures and minibasins formed through salt spreading, while the area offshore Boumerdès is characterized by gravity gliding due to the uplifted plateau. Although from this point of view the N-S compressional tectonics favors gravity gliding through the plateau uplift, on the other hand it influences the salt structure development direction, which present a mainly E-W development and a minor and delayed N-S one. A partial influence of the sedimentary body from Algerian rivers on the position of the major salt structures is inferred.

How to cite: Travan, G., Gaullier, V., Vendeville, B., Déverchère, J., Raad, F., and Lofi, J.: Gravity gliding and spreading in a compressional setting: the example of the Algerian margin, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11948, https://doi.org/10.5194/egusphere-egu21-11948, 2021.

11:45–12:30