TS10.1 | Salt-related deformation
EDI
Salt-related deformation
Convener: Marta Adamuszek | Co-conveners: Oscar Fernandez, Dan Mircea Tamas
Orals
| Tue, 25 Apr, 10:45–12:30 (CEST)
 
Room K1
Posters on site
| Attendance Tue, 25 Apr, 08:30–10:15 (CEST)
 
Hall X2
Orals |
Tue, 10:45
Tue, 08:30
The presence of salt, with its unique physical and mechanical properties, can strongly influence the deformation style of sedimentary rocks. Intra-salt compositional and lithological variation combined with various processes such as sedimentation, erosion, and tectonic activity can develop complex structures, within and surrounding the salt, which are often challenging to interpret. However, analysis of the structures and their formation is crucial for e.g., mineral and hydrocarbon exploration, designing safe underground magazines and repositories. Integrating the experience and knowledge from various disciplines can significantly increase our understanding of salt structures and salt-related deformation and also provide practical benefits. We thus invite contributions from various disciplines such as sedimentology, structural geology, tectonics, petrology, geophysics, experimental deformation, and numerical modeling.

Orals: Tue, 25 Apr | Room K1

Chairpersons: Dan Mircea Tamas, Marta Adamuszek
10:45–10:50
10:50–11:00
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EGU23-13289
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On-site presentation
Jean-Paul Callot, Leonardo Pichel, Etienne Legeay, and Jean-Claude Ringenbach

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.

11:00–11:10
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EGU23-3121
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ECS
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solicited
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Highlight
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On-site presentation
Leonardo Pichel, Ritske Huismans, Rob Gawthorpe, Jan Inge Faleide, and Thomas Theunissen

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.

11:10–11:20
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EGU23-5337
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ECS
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On-site presentation
Mercè Estiarte-Ruiz, Pablo Santolaria, Oriol Ferrer, Josep Anton Muñoz, Eduard Roca, and Marco Snidero

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.

11:20–11:30
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EGU23-11476
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ECS
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On-site presentation
David P. Canova, Zeina Naim, Eduard Roca, Oriol Ferrer, Frederic O. Escosa, and David Garcia-Sellés

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.

11:30–11:40
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EGU23-15386
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On-site presentation
Jean-Claude Ringenbach, Charlie Kergaravat, Charlotte Ribes, Alexandre Pichat, Etienne Legeay, and Jean-Paul Callot

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.

11:40–11:50
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EGU23-13682
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On-site presentation
Eduard Roca, Josep Oriol Ferrer, Mark Rowan, Josep Anton Muñoz, and Katerine Giles

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.

11:50–12:00
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EGU23-8229
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ECS
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On-site presentation
Gabriel Cofrade, Prokop Závada, Ondřej Krýza, Sadegh Adineh, Óscar Gratacós, Irene Cantarero, Oriol Ferrer, Eduard Roca, and Anna Travé

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.

12:00–12:10
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EGU23-12200
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On-site presentation
Mjahid Zebari, Anke Friedrich, Stefanie Rieger, Christina Plattner, Ramon Brcic, and Prokop Závada

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.

12:10–12:20
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EGU23-10828
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ECS
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On-site presentation
Sadegh Adineh, Prokop Zavada, Soraya Heuss-Aßbichler, Jiri Bruthans, Mathieu Daëron, and Daniel A. Petrash

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.

12:20–12:30
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EGU23-11382
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On-site presentation
Prokop Závada, Martin Staněk, Matěj Machek, Yves Géraud, Jiří Bruthans, and Aßbichler Soraya

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.

Posters on site: Tue, 25 Apr, 08:30–10:15 | Hall X2

Chairperson: Oscar Fernandez
X2.276
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EGU23-12189
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ECS
Michał Słotwiński, Ondřej Krýza, Prokop Závada, Michael Warsitzka, and Sadegh Adineh

Growth rate of salt diapirs usually oscillates depending on several factors. The growth can be arrested by depletion of the source layer or diapir burial, conversely, diapir reactivation occurs through erosion of the overburden and/or introduction of tectonic forces. Examples of reactivated diapirs can be observed in the Zagros Mountains in Iran. There, tectonic shortening responsible for development of the Zagros Fold and Thrust Belt simultaneously squeezes the diapirs, which extrude salt onto the surface. The top section of the diapir is usually affected by meteoric water, which dissolves the salt and leaves behind insoluble material embedded within the source layer, forming the so called caprock. This caprock can be assumed to be already present before the reactivation of the diapirs during shortening, hence it may play a role in the development of the salt extrusions. Geometry, composition and mechanical properties of the caprock can vary widely depending on factors such as original composition of diapiric material, dissolution and growth rates, etc. Additionally, exact mechanical properties of any caprock are difficult to determine and are currently largely unknown. 

Hence, we present a series of 2D numerical simulations utilising finite element method to investigate how different geometries and rheologies of the caprock affect the shape of the subaerial extrusions. The analysis was performed with three variable parameters (caprock viscosity, cohesion, and thickness) for three scenarios of diapirism (1 - purely shortening-based, with depleted source layer; 2 - purely buoyancy-based, with preserved source layer and no tectonic forces, and; 3) a combined scenario). We analysed the general deformation patterns as well as quantifiers such as velocities, displacements, strains, strain rates and ratios between vertical and horizontal components of the quantifiers. We investigated variability of averaged values of the quantifiers in time as well as detailed spatial distribution for the finite state of simulation. 

The simulations revealed the strong contrast between less (low cohesion and viscosity) and more competent rheologies in term of deformation patterns. The former tends to result in caprock material being thinly spread over the surface of the salt extrusion, whereas in the latter case the caprock fractures into “rafts” floating on top of the extrusion. The exact geometry of the rafts (size, spacing, distribution) is highly dependent on the geometry and type of diapirism. We also compare the resultant patterns to the quantifiers, especially velocities and their ratios, establishing clear ties between the patterns and deformation dynamics. 

How to cite: Słotwiński, M., Krýza, O., Závada, P., Warsitzka, M., and Adineh, S.: Influence of cap-rock on deformation during extrusion of salt diapir – a numerical study, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12189, https://doi.org/10.5194/egusphere-egu23-12189, 2023.

X2.277
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EGU23-14811
Stefanie Rieger, Prokop Závada, Jiri Bruthans, Christina Plattner, Ramon Brcic, Mjahid Zebari, Anke Friedrich, and Mugabo Dusingizimana

Salt diapirs are prominent features in the Zagros fold-and-thrust belt displaying complex interplay between the buoyant forces driving the rock salt to the surface, distribution of the caprock and erosion. The caprock represents the solid residue of salt dissolution in the apical part of the diapir. Understanding the dynamics of subaerial spreading of salt in salt glaciers therefore requires knowledge about the spatiotemporal surface deformation and the underlying controlling factors. However, the contemporary vertical surface-deformation pattern across salt diapirs is difficult to detect and interpret along disciplinary boundaries. Therefore, our goal is to analyse the active surface-deformation patterns of diapir-caprock systems in the Zagros, where diapirs and their caprocks are well exposed and accessible for field mapping. We primarily integrate high-resolution Persistent Scatterer Interferometry (PSI) and field mapping. We used Persistent Scatterer Interferometry (PSI) to obtain the highest available spatiotemporal resolution (on the range of mm/yr, ~12-day repeat cycle) of the vertical surface-deformation pattern across the Karmostaj and Siah Taq salt diapirs for which previous knowledge from detailed geological field mapping is available. Both diapirs contain a thick and deformed caprock layer on top or in the surroundings of the salt cupolas and are located 20 km south from the Lar city in southern Iran. We analysed the PSI-data using Sentinel-1 images acquired between October 2014 and December 2018 using the German Aerospace Center’s (DLR) Integrated Wide Area Processor (IWAP). First, the time-series analysis of the deformation signal in the line-of-sight is investigated for seasonal effects correlations, such as precipitation and heat. Second, the line-of-sight signal is split into vertical and horizontal components. In the next step, geological observations from field mapping provide the context to interpret the geodetic data. Preliminary results indicate that the deformation identified from PSI signal decreases outwards from the apical part for salt diapirs with thick caprock, as the caprocks and other residuals get relatively thicker above the underlying viscous salt. We postulate that the extra load the caprock body exerts on the underlying ductile salt drives subsidence in the crestal portion of the diapir. Understanding the spatiotemporal deformation pattern helps to recognize the impact of dissolution/erosion mechanisms and the distribution of caprock on salt diapirs. Therefore, careful analysis of geodetic signals, which requires contextual integration with geological field observations, reveals the influence of caprock on salt movement.

How to cite: Rieger, S., Závada, P., Bruthans, J., Plattner, C., Brcic, R., Zebari, M., Friedrich, A., and Dusingizimana, M.: Caprock matters: Surface deformation patterns of salt diapirs using high-resolution Persistent Scatterer Interferometry and geological field observations, Karmostaj and Siah Taq salt diapirs, Zagros mountains, southern Iran, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14811, https://doi.org/10.5194/egusphere-egu23-14811, 2023.

X2.278
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EGU23-747
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ECS
Nicolò Chizzini, Andrea Artoni, Luigi Torelli, and Mariagiada Maiorana

It has long been recognized that the central Adria Plate, as well as the Dinaric-Hellenic sector, contains a vast volume of Triassic salt associated with diapirism and it is well know that Triassic evaporites developed in the Mediterranean Sea region over epicratonic platforms. Nearby the Apennines and Dinaric-Hellenic front, several authors highlighted the presence of Triassic salt structures such as pillows, diapirs and salt walls, mostly triggered by Neogene tectonic shortening associated with the accretion of these opposite Chains. Nevertheless, in the Apulian foreland, representing the southernmost termination of the Adria plate the Northern Ionian Sea, Triassic evaporitic deposits have never been mapped due to the lack of explorative wells in this deepwater offshore sector. Based on seismic reflection profiles, we illustrate new evidences of Triassic evaporites in the Apulian foreland subsurface associated with two squeezed diapirs as evidence of regional shortening episodes, probably enucleated from inherited Mesozoic salt structures such as pillows and/or salt domes, thus implying new constrains on the paleogeographic reconstruction of the Northern Ionian Sea. The identification of halokinetic-related sequences up to the Plio-Quaternary foreland shallow sediments allows to constrain the evolution of the two diapirs. It results that they are reactivated till Plio-Pleistocene times in response to  the compressive stress trasmitted by the Southern Apennines/Calabrian Arc and Hellenides to the Apulian foreland. Later, after Middle Pleistocene, they were  dismembered by extensional tectonics related to Adria plate flexuring, as they represent areas of weakness. These observations make the regional geological contest one of the foundamental features controlling the Plio-Pleistocene Triassic evaporitic squeezing in the southern Adria Plate.

How to cite: Chizzini, N., Artoni, A., Torelli, L., and Maiorana, M.: Plio-Pleistocene rimobilization of a Mesozoic salt diapir in the Southern Adria Plate (Northern Ionian Sea, Central Mediterranean), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-747, https://doi.org/10.5194/egusphere-egu23-747, 2023.

X2.279
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EGU23-11705
Virginie Gaullier and Gaia Travan

The deposition during the Messinian Salinity Crisis (MSC, 5.96 – 5.33 My) of a thick layer of evaporites and especially of a mobile halite unit has deeply influenced the architecture and evolution of the Mediterranean margins. The Mediterranean has characteristics that set it apart from most “classic” salt-bearing basins, where salt was deposited after (or right after) the rifting stage. Conversely, in the Mediterranean, salt was not related to a rifting event and it covers vast areas that are geodynamically active presently. These include regions of divergence (Tyrrhenian Sea), young or mature convergence (Algerian and Ligurian Margins, Ionian Sea, Mediterranean Ridge), oblique convergence (Eastern Cyprus Arc), and strike-slip (Levant Basin). Despite the progress in seismic processing, the strong acoustic impedance contrast between salt and sediments prevents an accurate seismic imaging of the sub-salt deep structures. Second, the evaporites act as a decoupling layer (thin-skinned tectonics) preventing the propagation of the crustal structures towards the surface. Last, when crustal tectonics generates horizontal and vertical movements in the basement, these movements can trigger a gravitational response in the salt and its overburden, thereby blurring the deeper tectonic signal. In order to bypass these difficulties, we propose to use salt tectonics as a proxy to better constrain these deep structures both in terms of geometry and timing. Furthermore, the comparison between natural examples (seismic data) with analogue modelling allows a better understanding of the margins’ structure and evolution. We present here a synthesis of several Mediterranean study cases in different geodynamical settings (convergence, divergence, strike-slip). The complexity and variety of its margins, along with the presence of a widely distributed Messinian salt décollement, make the Mediterranean the perfect area to analyze salt deformation and its relationships with different tectonic styles, including the effects of crustal structures.

How to cite: Gaullier, V. and Travan, G.: Interactions Between Salt Tectonics and Crustal Tectonics in The Mediterranean, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11705, https://doi.org/10.5194/egusphere-egu23-11705, 2023.

X2.280
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EGU23-8063
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ECS
María Carrión-Jiménez, Antonio Teixell, Naiara Fernandez, Michael Hudec, María Luisa Arboleya, and Katherine A. Giles

The structural style of the High Atlas fold and thrust belt is controlled by precursor diapirs that initiated during preorogenic rifting episodes. In this work, we document and interpret the geometry and the along-strike variation of salt tectonic features on a particularly well-exposed salt ridge (the Aberdouz salt wall) that records tectonic evolution for linear diapiric structures from an extensional to contractional regime. The Aberdouz salt wall, cored by Triassic Keuper salt, was created during the Jurassic rifting of the Atlas domain, and was subsequently shortened during Cenozoic mountain building. The study presented is based on field observations, including geological mapping, definition of syn-growth stratigraphy, and the construction of serial cross-sections and sequential restorations.

The Aberdouz salt ridge trends ENE-WSW, is ca. 38 km long and is flanked by minibasins containing Jurassic growth strata up to 5 km thick. The minibasin fill displays a deepening to shallowing upward facies trend, from shallow water carbonates in the lower Lias, calciturbidites and shales (with marginal reefs) during the upper Lias-Dogger, grading finally into terrestrial red beds in the Bathonian-Callovian. Tectonosedimentary relationships indicate salt migration during deposition of the entire Jurassic megasequence. Although this sequence is modulated by salt withdrawal in depocenters, the general trend is governed by regional subsidence events in the Atlas rift. Lower sedimentation rates or interruptions during early Bajocian time are marked by synchronous salt-sheet extrusion on both diapir flanks, overlapped by condensed-fauna intervals.

The Aberdouz diapiric core is welded in many places along the length of the ridge, but is still partly open where inclusions (Triassic basalts, Jurassic carbonates or late Jurassic gabbro-syenite bodies) prevented complete welding. Keuper red-green shale and gypsum is locally preserved, but halite is never exposed. The absence of metamorphic aureoles around the gabbro-syenite plutons suggests magmatic intrusion into weak salt-rich Keuper bodies, which were subsequently expelled during the Cenozoic shortening. Steeply upturned stratal panels flanking the diapirs or welds contain homoclinal, near-isopachous, but thickened Jurassic sequences concordant with the Triassic, indicating original deposition on the minibasin floor followed by upthrust and rotation to a diapir-flanking position. In contrast, diapiric stocks oriented transverse and splaying from the main salt wall preserve halokinetic sequences and along-strike turtle structures, indicating they have experienced less distortion and stratal rotation during Cenozoic shortening.

Finally, the Aberdouz ridge offers the opportunity to study salt wall terminations, which are different from each other: at one end of the diapir, the termination is marked by a large Q-tip stock (with inclusions) and at the other end the salt wall and megaflap are terminated against by a sharp tear fault.

How to cite: Carrión-Jiménez, M., Teixell, A., Fernandez, N., Hudec, M., Arboleya, M. L., and Giles, K. A.: Anatomy and evolution of a salt wall from halokinesis to contraction (Central High Atlas, Morocco), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8063, https://doi.org/10.5194/egusphere-egu23-8063, 2023.

X2.281
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EGU23-5438
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ECS
Dan Mircea Tamas, Alexandra Tamas, Daria Dohan, Ioana Silvia Mihaela Tocariu, Zsolt Schleder, Csaba Krezsek, and Janos Urai

Salt is present in many orogenic fold-and-thrust belts and it serves as an excellent décollement. This often leads to a localization of deformation (folds and thrusts) within the salt or to the development of salt diapirs. The Romanian Carpathians provide a natural laboratory for the study of salt tectonics in orogenic settings because of the mix of available data. The subsurface data was acquired mostly for hydrocarbon exploration and production but provides aid in the regional understanding of structural style, salt mines offer excellent exposures of cleaned walls and some amazing outcrops that can be used for taking samples and detailed measurements.

The layered rock salt exposed along the Carpathians strongly varies in impurity content, ranging from clean, almost 99% pure halite to salt rich in impurities ranging from micrometer to meter-scale fragments of various lithologies (sandstones, limestones, green schists, and volcanics). Studying these exposures and the difference in deformation and mechanical behavior of impure halite-dominated salt is of high importance when predicting the long-term evolution of underground storage caverns and nuclear waste repositories.

Here, we present how we combine classical fieldwork methods with UAV-based digital outcrop models, with microstructure and composition analysis to gain insights into the long-term deformation and properties of rock salt.

 

Acknowledgments: DMT acknowledges the financial support of UEFISCDI grant PN-III-P1-1.1-PD-2021-0165

How to cite: Tamas, D. M., Tamas, A., Dohan, D., Tocariu, I. S. M., Schleder, Z., Krezsek, C., and Urai, J.: Salt tectonics and its influence on the development of the Romanian Carpathians, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5438, https://doi.org/10.5194/egusphere-egu23-5438, 2023.

X2.282
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EGU23-2683
Marta Adamuszek and Piotr Krzywiec

The presence of the thick Zechstein (Upper Permian – Wuchiapingian to Changshingian) evaporites strongly controlled deformation style within the Polish Basin that formed the eastern periphery of the epicontinental Permian-Mesozoic Central European Basin System, both during its Triassic to Early Cretaceous subsidence as well as during its Late Cretaceous to Paleogene inversion. Traditionally, formation of Zechstein evaporites has been associated with deposition of evaporitic cyclothems within large depression, with essentially no tectonic influence on evaporitic depo-systems. Furthermore, development of salt structures, in particular of salt pillows, has been commonly attributed to thin-skinned tectonics with minor role played by sub-salt fault zones. A newly developed tectono-stratigraphic model, constructed using seismic data calibrated by deep research wells from the central part of the basin (Bydgoszcz – Szubin area), suggests a significant role of Late Permian localized extension and deposition of syn-extensional Zechstein evaporites within the half-graben controlled by a deeply rooted normal fault. Consecutive basin inversion was associated with substantial uplift of the hangingwall block, formation of salt pillow built of locally overthickened evaporites deposited during active extension, and buckling of the Mesozoic supra-salt overburden. In order to test this new tectono-stratigraphic scenario of deposition and deformation of the Zechstein evaporites our own finite element-based numerical model has been used. In this study, we considered a two-dimensional plane strain model. The deformation was studied using the incompressible Stokes equations. A simplified stratigraphic sequence of the evaporitic series composed of alternated salt and anhydrite layers with a total initial thickness of 1 km has been used as it depicts general characteristics of the initial model constructed using seismic data. In several model runs, various geometrical and mechanical parameters of the salt and anhydrite layers and of the overburden have been considered. Additionally, various scenarios of deformation including the different rates of deformation and fault basement activity have been tested. We also took into account various models of sedimentation and erosion processes. Obtained results fully confirmed that indeed basement localised subsidence and later inversion might have played a much more important role during the deposition of Zechstein evaporites and then during the formation of salt pillows than previously assumed.

How to cite: Adamuszek, M. and Krzywiec, P.: Role of buckling and sub-salt basement activity on the evolution of salt pillow structure – insights from numerical models and seismic data from the Polish Basin, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2683, https://doi.org/10.5194/egusphere-egu23-2683, 2023.

X2.283
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EGU23-13369
Internal structure of the evaporite sequence and its underground storage potential: case study from the northern part of the Polish Zechstein basin.
(withdrawn)
Marta Tomaszczyk, Marta Adamuszek, and Grzegorz Czapowski