Salt-bearing rifted margins comprise some of the most structurally complex and economically important sedimentary basin settings such as the South Atlantic and the Gulf of Mexico salt basins. They are also involved with some of the largest uncertainties regarding the crustal and syn-rift basin architecture and supra-salt tectonic evolution, as well as the link between rifted margin architecture with salt deposition and post-rift gravity-driven salt tectonics. We thus conduct a margin-scale study along nearly the entire West Africa salt basin, from south Gabon to Namibe, combining a vast dataset of 2D and 3D seismic and well data with gravimetric and magnetic data to analyse its along-strike rift and salt tectonics structural variability. We construct regional structural and thickness maps of key salt and post-salt intervals to depict the history of individual margin segments and to investigate: 1) how rifting and rifted margin architecture influences post-rift salt tectonics evolution, 2) how these vary through time and space, and 3) what are the controls between their different salt tectonics structural styles. We show that rifting and rift structures controlled the salt basin geometry, thickness, and base-salt relief in different ways for the different margin segments, and drastically influenced their post-rift salt tectonic evolution. Differences in post-salt sediment supply and continental uplift also had a role on their evolution. The results also have implications to understand the interplay between rifted margin architecture with post-rift salt tectonics for worldwide salt-bearing margins.

How to cite: Callot, J.-P., Pichel, L., Legeay, E., and Ringenbach, J.-C.: The salt-bearing rifted margins in West Africa – regional structural variability and salt tectonics between Gabon and Namibia, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13289, https://doi.org/10.5194/egusphere-egu23-13289, 2023.

The largest and majority of salt basins form along rifted continental margins during the latest stages of rifting and prior to continental breakup. We use 2D thermo-mechanical finite-element modelling of lithospheric extension to investigate the interplay between rifted margin architecture, late syn-rift salt deposition, and post-rift salt tectonics across different types of continental margins. We evaluate the: 1) interplay between syn-rift extension, salt deposition and post-rift salt tectonics, 2) influence of salt basin architecture on salt flow, 3) distribution of salt-related structural domains, and 4) contrasting salt tectonic styles for different margin types. Narrow margins form partially-isolated salt sub-basins with prominent base-salt relief, limited translation but significant diapirism and minibasin development. Wide margins form wide salt basins with subtle base-salt relief, pronounced seaward salt expulsion and overburden translation, which result in updip extension with development of post-rift normal faults and rollovers, mid-margin translation and downdip diapir shortening. All margins develop a distal salt nappe that varies in width and complexity. The contrasting styles of diapirism and minibasin geometries as well as basin-scale salt deformation between different margin types are controlled by margin width, base-salt relief, salt thickness and the relative rate of progradation. The results are comparable to several examples of salt-bearing rifted margins worldwide, from minibasin- to margin-scale, and improve our understanding of their dynamics and structural variability.

How to cite: Pichel, L., Huismans, R., Gawthorpe, R., Faleide, J. I., and Theunissen, T.: Geodynamic modelling of salt-bearing rifted margins: from minibasin- to margin-scale salt tectonics across different margin types, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3121, https://doi.org/10.5194/egusphere-egu23-3121, 2023.

The Cotiella Massif is included in the Cotiella-Bóixols thrust-sheet, one of the three imbricated thrust sheets of the South-Pyrenean thrust system. It originated from the inversion of the Cotiella Basin, a post-rift gravity-driven salt-bearing assemblage of isolated sub-basins. On them, upper Albian to lower Coniacian post-rift carbonate platforms collapsed above Upper Triassic evaporites (Keuper facies), and middle Coniacian to lower Santonian minibasins developed during the margin failure due to salt evacuation and gravity-driven extension. Seismic scale rollovers developed in the hanging wall of basinward-dipping listric faults isolating four sub-basins: Cotiella, Armeña, Peña del Mediodia, and Seira. Additionally, structural and sedimentological evidence suggests passive diapirism at the footwall of these faults. Upon the Pyrenean orogeny, diapirs were rejuvenated, squeezed and welded, faults were positively inverted, and the salt-detached gravity system was incorporated into the orogen.

In this work, we present a detailed geological map of the Cotiella Basin around the Reduno downward-facing anticline which represents the basinward northern edge of the Cotiella sub-basin and its contact with the Armeña sub-basin. Based on this map, more than 1.700 dip data, and comprehensive image interpretations, a stepwise restoration of a representative cross-section has been done to unravel the geological evolution of the basin from the early stages of development to its subsequent contractional deformation. On it, a flap and halokinetic sequences can be identified. Furthermore, a regional and a counter-regional extensional fault system affecting early syn-kinematic strata have been recognized, nowadays highly folded and overturned due to inversion. In addition, the later contractional deformation related to the Pyrenean orogeny has also been inferred, highlighting the role of inherited extensional and salt tectonics structures during the inversion.

How to cite: Estiarte-Ruiz, M., Santolaria, P., Ferrer, O., Muñoz, J. A., Roca, E., and Snidero, M.: From salt-detached gravity-driven extension of a rifted margin to its inversion: The Cotiella Massif case study (Southern Pyrenees), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5337, https://doi.org/10.5194/egusphere-egu23-5337, 2023.

The Eastern External Betics correspond to the external part of the Betic fold-and-thrust belt that crops out in the Valencia and Alicante provinces. It mainly consists of a system of ENE-trending cover folds and thrust sheets detached in the Triassic salt along with a significant amount of diapirs and allochthonous sheets made by this salt. Most primary diapirs formed during the extensional evolution of the southern Iberian passive margin during Jurassic to early Santonian time. These diapirs were later shortened and squeezed forming syn-contractional salt sheets and secondary minibasins during the Africa/Eurasia convergence that, beginning at late Santonian times, led to the formation of the Pyrenean and Betic orogens.

Based on detailed stratigraphic analysis, structural field mapping, fracture analysis, and by comparison with other salt-bearing fold-and-thrust belts we revisit one of the major allochthonous salt sheets of the area, the Elda salt sheet, to reinterpret its structural evolution. The Elda salt sheet includes fragments of the feeding diapir roof as well as secondary minibasins made by late Santonian to middle Miocene syn-contractional sediments and it is covered by upper Miocene to Pliocene post-contractional deposits.

This presentation will focus on the evolution of the El Bolon and Bateig secondary minibasins. El Bolon minibasin is characterized by a basal section comprising Late Cretaceous (Senonian) marls that correspond to the carapace above a diapir. The Senonian sequence is conformably overlain by Paleocene-Eocene siliciclastics that are characterized by a series of syn-sedimentary normal faults that sole into the salt with significant variations in thickness throughout the minibasin. In Oligocene times, coeval with the onset of the Betic Orogeny, renewed diapirism resulted in the extrusion of allochthonous salt and dismembered the diapiric roof. Diapir derived detritus (Jacintos de Compostella) in the Oligocene-Miocene sequence indicate that allochthonous salt was exposed at the surface while El Bolon minibasin continued to passively grow. Throughout the Early to Middle Miocene El Bolon minibasin developed hook halokinetic sequences and episodic unconformities with onlaps recording the progressive rotation of the minibasin. By the end of the Middle Miocene the whole minibasin was completely encased in salt. Coeval to or shortly after the encasement of the El Bolón minibasin the Bateig minibasin, comprising Miocene calcarenites and siliciclastics, began to subside into the allochthonous sheet. Continued shortening due to the Betic Orogeny further rotated the El Bolón minibasin around a horizontal axis to its present position (vertical to overturned) contemporaneous with the southward tilting and partial encasement of the Bateig minibasin.

How to cite: Canova, D. P., Naim, Z., Roca, E., Ferrer, O., Escosa, F. O., and Garcia-Sellés, D.: Structural analysis and tectonic evolution of the El Bolon and Bateig secondary minibasins in the Eastern External Betics (Betic fold-and-thrust belt—Iberian Peninsula), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11476, https://doi.org/10.5194/egusphere-egu23-11476, 2023.

The outstanding outcrops of salt tectonic structures of the Sivas basin in Anatolia are now well known. A drone acquisition in November 2018 provides 3D images to visualize and interpret the structures in order to better analyze subsurface data from salt domains and since, many puctures have been acquired by the first author with a Mavic drone. Drone images, now widely used in structural geology, allow building 3D qualitative models of the outcrops. Seven structures among the most demonstrative of salt tectonics have thus been imaged in the secondary minibasins.

The Sivas basin, an elongated Oligo-Miocene north-verging multi-phased foreland basin, developed above the Neotethys suture zone. Evaporites deposited at the end of the early compression phase (Bartonian), filled the foreland basin and covered eroded thrust sheets and folds to the south. Primary minibasins formed during a period of quiescence from Late Eocene to Early Oligocene, associated to the building of an evaporite canopy. The system further evolved during convergence of the Arabian and Eurasian plates in the Late Oligocene-Early Miocene with a renewed compression on the north verging fold-and-thrust belt (FTB). This resulted in the formation of secondary minibasins, ultimately tilted and welded.

In the last decades, huge improvements in seismic imaging under thick allochthonous salt have been made in the Gulf of Mexico and Angola. Wide-azimuth towed-streamer (WATS) 2D as well as 3D seismic acquisitions allow far better imaging along steep subsalt diapiric flanks and welds. However, major drilling disappointments still do occur, due to unseen megaflaps and small-scale structures such as halokinetic sequences at various scales or small faults cannot be seen. Field analogs then become the only guide for a better assessment of the traps. Striking geometric analogies between the Sivas outcrops and seismic images from the classic petroleum provinces controlled by salt tectonics will illustrate the extraordinary quality of the Sivas basin as a geometrical field analog for the Angola and the Gulf of Mexico salt basins. Analog modelling imaged with X-ray tomography under a medical scanner will also be used for comparison.

How to cite: Ringenbach, J.-C., Kergaravat, C., Ribes, C., Pichat, A., Legeay, E., and Callot, J.-P.: Salt Tectonics Outcrops and 3D Drone Images from the Sivas Basin (Turkey) compared to High-Resolution Seismic Lines, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15386, https://doi.org/10.5194/egusphere-egu23-15386, 2023.

The Bakio Diapir is one of the few exposed deepwater passive diapirs, with both synkinematic carbonate and siliciclastic strata. It is located at the northern margin of the Basque-Cantabrian Basin. This basin developed between the Iberian and Eurasian plates during the latest Jurassic-Cretaceous opening of the Bay of Biscay and was later inverted during the Pyrenean orogeny (Late Cretaceous -Santonian- to middle Miocene) forming the Basque Pyrenees.

 This work evaluates growth strata adjacent to this diapir aiming to discuss the application of halokinetic-sequence concepts, mainly developed in shallow-water to subaerial environments, to deepwater depositional settings. We present a 3D analysis of this outstanding salt structure by integrating detailed geological maps, high-resolution bathymetry, seismic, and well data. The resulting reconstruction enables us to trace 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 evaluate the factors controlling the configuration of halokinetic sequences in deepwater environments. The main results of our study show that:

 A) The geometry of the halokinetic sequences is defined, regardless of setting, by the thickness of the roof edges. Thus, thick diapir roofs generate wedge HS and tapered CHS, and thin diapir roofs form hook HS and tabular CHS.

B) The thickness of the diapir roof is often controlled by the ratio between salt-rise and local sediment-accumulation rates but also, in carbonate environments, by the water depth of the diapir roof and the environmental conditions that can promote aggradation of a carbonate buildup on top of the diapir. Thus, thick diapir roofs and tapered CHS can form even though the ratio was high in this case due to slow, marly deposition in the minibasins.

 C) The diapir roof thickness is also controlled in shallow-water carbonate settings by the accommodation space available over the top of the diapir, which itself is determined by: a) sea-level fluctuations; and b) the interplay between the uplift of diapir top and the regional/ local tectonic subsidence of the diapir base.

D) High and steep scarps over the edges of diapirs, and thus abundant debrites, are not exclusive to hook HS and tabular CHS. They can be also present in wedge HS and tapered CHS that formed from the aggradation of a thick carbonate buildup on top of a diapir.

How to cite: Roca, E., Ferrer, J. O., Rowan, M., Muñoz, J. A., and Giles, K.: Interplay between bathymetry, subsidence, and sedimentation in the configuration of halokinetic sequences at the deepwater Bakio Diapir (Basque-Cantabrian Basin, Pyrenees), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13682, https://doi.org/10.5194/egusphere-egu23-13682, 2023.

Salt sequences usually contain interbedded, non-saline, sedimentary layers (carbonates, sulphates, and siliciclastics) which behave as brittle, competent layers entrained within the weak, viscous salt. These layers become fragmented, and further stretched and folded as the host rock salt is mobilized. In diapirs reaching the surface, fragments of these brittle layers (stringers) can be transported upwards along the diapir stem from their source layer and then laterally and sometimes gravitationally downwards in the allochthonous salt sheets, becoming embedded in the diapir caprock as the salt is dissolved by unsaturated fluids. Therefore, the stringers arrangement may serve as a proxy to understand salt flow. To test this hypothesis, we have examined the internal structure of the Les Avellanes diapir rocks (South-Central Pyrenean fold-and-thrust belt) which represents a syn-orogenic laterally advancing salt sheet, early Oligocene in age. To understand the internal structure, the diapir exposure has been mapped in detail and projected in a cross-section along the expected flow direction. Then, to evaluate this structure in terms of flow kinematics and dynamics, we have reproduced the Les Avellanes lateral salt sheet with analogue models equipped with a stereographic system of strain quantification (LaVision GmbH).

The Les Avellanes Diapir exposes a gypsum rich caprock with numerous Triassic carbonate and subvolcanic stringers, which were carried along within the diapir stem and salt sheet. The carbonate stringers show contrasting bottom and top facies (laminated vs. tabular) constraining their stratigraphic polarity. The stringers are mainly subvertical in the diapir stem and around the probable crestal/feeder area, flat lying stringers are disrupted by several extensional faults. Towards the allochthonous salt body, they are obliquely or vertically imbricated with some of the stringers overturned. This suggests that stringers were carried through the feeder conduit to the surface, then became stretched horizontally in the feeder area and imbricated and stacked within the laterally advancing salt sheet.

This hypothesis has been evaluated using analogue models. The modelling setup consisting of a box with a moving wall to simulate shortening, and two silicone layers (polydimethylsiloxane) separated by two thin, colored granular layers (simulating carbonate layers disrupted into stringers). The host rock overburden, represented by colored sand, is continuously sieved around a rectangular vertical conduit of the diapir. During shortening, caprock made of cohesive material (glass beads) is added on top and syn-kinematic sand layers are added adjacent to the laterally advancing silicone extrusion. In the cross-sections of the models, stringers are verticalized in the diapir conduit, parallel to the walls, and distorted into isoclinal folds with downflow vergence in the advancing allochthonous extrusion. The surface strain pattern revealed extension around the crestal area, and belts of contraction downslope in the advancing body developing in sequence backwards from the front as caprock rafts and stringers continuously became imbricated, blocking and decelerating the flow. As the internal structure of the deformed stringers is compatible with field observations, similar strain patterns visible in the model may be attributed to the development of this salt sheet.

How to cite: Cofrade, G., Závada, P., Krýza, O., Adineh, S., Gratacós, Ó., Cantarero, I., Ferrer, O., Roca, E., and Travé, A.: Internal structure and salt flow in the Les Avellanes allochthonous salt sheet: insights from field observations and analogue modelling comparison, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8229, https://doi.org/10.5194/egusphere-egu23-8229, 2023.

In the emergent (subaerial) salt diapirs, the salt faces negative buoyancy when extruded to the surface, and flows outward around their vent by gravity spreading. It also faces dissolution and erosion. Salt supply, salt flow, dissolution, and erosion also influence the diapir’s shape. Although satellite geodesy monitors the surface deformation of the salt-caprock glacier system, the interpretation of the resulting deformation pattern in terms of salt supply, dissolution, and erosion is not straightforward. To overcome these shortcomings, we analyze surface deformation pattern of a fountain-shaped and nearly symmetrical diapir (Finu) within the Zagros Belt of Iran using Persistent Scatterer Interferometry (PSI). The PSI data are extracted from the Sentinel-1 SAR images using the Integrated Wide Area Processor (IWAP) at the German Aerospace Center (DLR) covering four years from October 2014 to December 2018. The line-of-sight signal from the PSI data is decomposed into the vertical and horizontal deformation signals. Within the diapir, the deformation signal is then spatially correlated with the influencing factors, including local position within the diapir, slope, karstification, and drainage. Along an E-W profile across the diapir, two-dimensional deformation vectors reflect salt supply and spreading; therefore, the magnitude and direction of these vectors are influenced by their local position within the diapir and the slope. There is a slight uplift in the central part of the salt domes with active salt extrusion. The deformation vectors divert outward in the slope direction, and the deformation reaches its maximum magnitude at the upper flanks of the central dome. The deformation decreases in the outer flat plateau regions of the extrusions and continues to decrease in the steep slopes at their lateral terminations. Along the same profile, relatively higher subsidence is detected in areas where sinkholes are abundant. In these regions, salt is removed in the subsurface by dissolution-driven karst development in contrast to areas where the surface drainage system is developed, and fluvial erosion is dominant. In the future, a better understanding of the factors controlling salt spreading around the vent and the impacts of dissolution/erosion mechanisms on the deformation will improve our ability to interpret surface deformation of the salt-caprock system at unprecedented spatial and temporal resolution.

How to cite: Zebari, M., Friedrich, A., Rieger, S., Plattner, C., Brcic, R., and Závada, P.: The role of salt supply, dissolution, and erosion on the surface deformation of emergent salt diapirs based on analysis of Persistent Scatterer Interferometry data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12200, https://doi.org/10.5194/egusphere-egu23-12200, 2023.

The eastern Zagros Fold and Thrust Belt (ZFTB) in Iran includes a salt tectonic province with roughly 130 salt-gypsum diapirs emerging within the Neoproterozoic-Early Cambrian Hormuz Complex. The diapirs in the ZFTB differ in composition and in their distribution of exposed caprock mélanges (CRMs). Although there are numerous studies focused on the geochronology and geochemistry of igneous rocks as exotic blocks associated with CRMs, the geochemistry, and petrography of carbonates remain to be systematically investigated. The Paskhand Diapir is a unique little diapir with no visible salt rock at the surface. Its CRMs consist of massive and layered gypsum, carbonate, marlstone, and siltstone,  which are associated with diabase exotic blocks. The carbonate paragenesis is being examined. A grey fine crystalline  dolomite is considered to have originated early during diagenesis from a Neoproterozoic marine environment. Other carbonates can be distinguished on the basis of their microspar, and spar cements. In general, the major minerals are dolomite and calcite, with quartz and iron oxides being in minor abundance. Important trace minerals are pyrite, sphalerite, talc, mica, K-feldspar, malachite, bassanite, rutile, chlorite, and apatite. Their abundance in mineral assemblages is variable, also depending on the locality within the diapir. Later-stage calcitic veins frequently cross-cut through micritic and microspar cemented lithologies. Lithological mapping shows that the edge of the diapir commonly exhibits a greater variety of mineralization modes with extensive recrystallization as compared with its core. The δ13C values of dolomite range from –7.0 to +2.7 ‰ V-PDB. This range indicates that seawater was the principal source of reactants for dolomite precipitation, although with some inorganic carbon derived from organic matter oxidation. The δ18O values of dolomite range from –0.55 to –13.13‰ V-PDB, reflecting a temperature fractionation effect. The carbonate formation temperatures of the Hormuz complex (both veins and host rock) were determined for the first time by using the Δ47 (paleo)thermometer in dolomite. Δ47 values range between 0.422 ± 0.015 and 0.287 ± 0.015 ‰, indicating diagenetic closure temperatures of between 116.4 ± 11.7 and 271.2 ± 32.5  ºC. An intensive interaction of hydrothermal fluids with the host rock during localized carbonate recrystallization is thus evidenced.

These results show that a correct interpretation of the mechanism(s) of carbonate alteration is critical for reconstructing the history of diapirism in the area. We hypothesize that carbonates in CRMs were reworked through a series of events largely influenced by thermochemical sulfate reduction (TSR) at T ≥ 110 ºC. 

How to cite: Adineh, S., Zavada, P., Heuss-Aßbichler, S., Bruthans, J., Daëron, M., and A. Petrash, D.: Carbonate formation and alteration in the salt diapir caprock (Paskhand salt diapir, Southern Iran), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10828, https://doi.org/10.5194/egusphere-egu23-10828, 2023.

Caprock on the top of salt diapirs represents the accumulated solid residuum left behind after the salt dissolution by meteoric fluids or deeper cognate fluids from surrounding rock formations. It usually consists of the sulphate matrix-supported sedimentary breccia with clasts representing the various rock types incorporated in the original evaporite sequence that were dismembered and transported towards the surface within the rock salt. Since salt diapirs are important targets of hydrocarbon repositories, salt caprock physical properties, namely the permeability, are critical for safety evaluations of such facilities. Caprock itself can become a hydrocarbon reservoir. 

In this study, we present a microporosity and microstructural analysis of a series of samples from the Karmostaj and Siah Taq diapirs, located 20 km south of Lar city in Southern Iran. Both diapir exposures resemble salt glaciers and contain caprock deformed to a different degree above the rock salt outcrops. Mercury intrusion porosimetry was employed on 13 samples, each represented by 2-3 specimens. The selected samples represent an unaltered micritic dark dolomite, vuggy dark dolomite, undeformed and deformed sulphate matrix-supported breccia (floatbreccia), clast-supported breccia (packbreccia) and gypsum mylonite enclosing the vuggy carbonate clasts. 

Microstructural study identified reactions of carbonate replacement by gypsum in the vuggy carbonates, typified with vuggy or channel-like porosity. Clast-supported breccia is characterized by fractures and interparticle voids. The porosity of matrix-supported breccia (floatbreccia) is defined by inter-particle voids, foliation parallel high-porosity bands and gypsum foliation parallel fracture porosity, prominent in the highly deformed samples. The porosity values are the lowest in the micritic dolomite (2.4 - 4.2 %) with unimodal throat size (TSD) distribution of the pores at 0.1 μm. In contrast to the unaltered dolomite, the vuggy dolomite features very high porosity from 28 to 33 % connected by throats with a large span of sizes 6 to 60 μm and their average median throat size (MTS) is 23 μm. The breccia types have intermediate porosities between 15 and 23 % and differ markedly in the position of the dominant peak of their TSDs: 0.7 - 2.8 μm for the packbreccia and 20 μm for the floatbreccia. The free porosity is high (4 to 6 %) in both the types of packbreccias and low (1 to 2 %) in the floatbreccia. The gypsum mylonite features low porosity between 6 and 10 % and very low-size TSD between 6 and 40 μm.

We present a model of the microporosity evolution on the basis of caprock structure reconstruction and comparison of the porosity values and microstructures of the samples. The model proposes an important role of sulphate-rich fluids that dissolve the solid rafts of dark carbonate blocks that become partly replaced by gypsum. Consequently, deformation of caprock culminating at the lower edges of the salt glaciers is responsible for collapse of interclastic pores and development of fracture cleavage along the deformation fabrics of dynamically recrystallized gypsum. Sulphate rich fluids percolating through the caprock also promote local overpressure-driven fracturing along ductile shear zones.

How to cite: Závada, P., Staněk, M., Machek, M., Géraud, Y., Bruthans, J., and Soraya, A.: Microporosity evolution of naturally deformed caprock on salt diapirs in southern Iran, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11382, https://doi.org/10.5194/egusphere-egu23-11382, 2023.