TS11.1

Salt Tectonics Outcrops and 3D Drone Images from the Sivas Basin (Turkey) compared to High-Resolution Seismic Lines

Jean-Claude Ringenbach^1*, Charlie Kergaravat¹, Charlotte Ribes¹, Alexandre Pichat², Etienne Legeay² & Jean-Paul Callot²

1 TotalEnergies s.e., Av. Larribau, 64018 Pau cedex, France.

2 LFC-R, Université de Pau et des Pays de l’Adour, Avenue de l’Université, BP 576, 64012 Pau cedex, France.

* Corresponding author: jean-claude.ringenbach@total.com

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. R.: Salt Tectonics Outcrops and 3D Drone Images from the Sivas Basin (Turkey) compared to High-Resolution Seismic Lines, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1174, https://doi.org/10.5194/egusphere-egu22-1174, 2022.

Salt welds are frequent features in basins with halokinesis. They are profusely observed on reflection seismic and are common features on maps of salt-rich geological provinces (even though they may not always have been identified as such). Despite this abundance, detailed studies of salt weld outcrops are remarkably scarce, in part due to outcrop conditions being hampered by vegetation and weathering. This results in a significant paucity in the description of the structure of salt welds at the meter- to centimeter-scale.

In this contribution we present our observations on three non-primary salt welds from the Northern Calcareous Alps (NCA) in the Eastern Alps, an area that evolved from a Permian-Jurassic passive margin setting to the Cretaceous-Recent Alpine orogenesis. The NCA are dominated by Triassic to Jurassic shallow to deep water carbonates, underlain by an Upper Permian evaporitic unit (mainly salt, anhydrite and shales). The evaporite unit is preserved at present mostly in broad, poorly outcropping salt bodies (salt walls?) located between blocks of Triassic platforms, and in diapirs and allochthonous bodies that are mined or quarried for halite and anhydrite. These bodies have been affected by Alpine orogenesis to different degrees, but in general present a strong contractional and/or strike-slip overprint.

In this presentation we discuss welds that are associated to two diapirs and potentially to a strongly overprinted salt wall. Outcrop conditions for the welds are outstanding, with two of these welds being observed in the galleries of two salt mines. All welds occur in Middle to Upper Triassic platform carbonates and contain no major traces of evaporites but do contain either highly sheared syn-evaporite shales or fragments of Lower to Middle Triassic post-salt sediments. Hand samples and outcrop observations have been used to describe the millimiter- to hectometer-scale structure of the welds and provide a unique insight into the detailed architecture of salt welds. Furthermore, it reveals a different tectonic evolution for each weld, with different relative contributions of halokinesis and faulting during the passive margin stage, and of re-activation during Alpine orogenesis.

How to cite: Fernández, O., Grasemann, B., Ortner, H., Szczygiel, J., and Leitner, T.: Salt welds from up close: Examples from the Eastern Alps, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7092, https://doi.org/10.5194/egusphere-egu22-7092, 2022.

The reserves of hydrocarbon reservoirs with gypsum-salt rock as cap rock account for 55% of the total hydrocarbon reserves in the world. The influence of cap rock sealing ability is an important problem to be solved in hydrocarbon accumulation analysis. Gypsum-salt rock belongs to evaporite, which is often associated with mudstone, limestone and dolomite, resulting in extremely complex lithologic composition of gypsum-salt rock caprock. At present, the analysis of sealing capacity of gypsum-salt rock caprock lacks the distinction between gypsum rock and salt rock, and the previous comprehensive evaluation of sealing capacity of caprock mainly focuses on the macro and micro characteristics of caprock. As one of the influencing factors of sealing capacity - mechanical properties, they are ignored in the evaluation system of sealing capacity of caprock.

Based on this, the classification standard of gypsum-salt rock caprock type is established, and the gypsum-salt rock caprock is divided into "three categories and five sub categories". Comprehensively considering the macro and micro characteristics and mechanical properties of the caprock, the lithology and rock combination type, lithology zoning, cumulative thickness of dominant lithology, caprock thickness, maximum thickness of thick single layer, ground coverage ratio, internal friction coefficient, tensile strength and peak strength are selected as the evaluation factors. The analytic hierarchy process (AHP) is introduced to determine the weight of each factor, formulate the evaluation standard, and establish the evaluation system of gypsum-salt rock caprock based on AHP to realize the quantitative evaluation of the sealing capacity of gypsum-salt rock caprock.

The evaluation method is applied to the Cambrian gypsum salt caprock in Tarim Basin, China. The results show that the C value in Bachu area of Tarim Basin is between 2.6-3.9, with an average value of 3.3, and the caprock quality is good; The C value in Tazhong area is 1.8-22, with an average value of 2.0, and the sealing capacity of caprock is generally general; The C value of Tabei uplift is less than 2, and it is in the range of poor caprock as a whole. On the whole, the evaluation value of sealing capacity of gypsum-salt rock caprock in Tabei—Tazhong—Bachu area gradually increases and the sealing capacity gradually becomes better. Combining the evaluation results with the vertical distribution of hydrocarbon, the corresponding vertical display type of hydrocarbon is mainly the distribution type under salt rock, and the corresponding hydrocarbon distribution position of poor caprock is above salt. The evaluation results are highly correlated with the vertical distribution of hydrocarbon, It shows that the evaluation system is of great significance for accurately evaluating the sealing hydrocarbon ability of gypsum-salt rock caprock and guiding hydrocarbon exploration.

Keywords: gypsum-salt caprock; lithological combination; sealing ability; quantitative evaluation; Tarim Basin

How to cite: Zhao, S.: Quantitative evaluation of the sealing ability of gypsum-salt rock caprocks, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1396, https://doi.org/10.5194/egusphere-egu22-1396, 2022.

As a part of the intracontinental Central European Basin System, the Baltic sector of the North German Basin has a long and complex history of basin evolution strongly influenced by salt tectonics. In the scope of the DFG project StrucFlow, we investigate the Triassic – Jurassic phase of basin evolution of the Baltic sector of the North German Basin to deepen the understanding of regional tectonics and their relation to the initial development of Zechstein salt structures. We use a dense network of modern marine high-resolution 2D seismic profiles together with older seismic data and both onshore and offshore wells. Thereby, we strive for a detailed regional tectono-stratigraphic interpretation of Triassic and Jurassic deposits with improved stratigraphic subdivision. We interpret local thickness variations across salt structures, imaged by the seismic data, to identify phases of salt withdrawal in rim-synclines and accumulation within the salt structure. Our analysis covers the northernmost part of both the eastern Glückstadt Graben and the Eastholstein Mecklenburg Block as well as the northeastern basin margin close to Rügen Island. Relatively quiet tectonic conditions characterized by thermal subsidence during the Early and Middle Triassic persisted in the study area. In the Late Triassic, during deposition of the Keuper, Paleozoic faults were reactivated at the northeastern basin margin, which created a local depocenter with increased thickness of Keuper and Lower Jurassic deposits. We interpret this zone with increased Triassic – Jurassic sedimentary thickness as a transtensional graben system connected to deeper Paleozoic structures. Local thickness variations of Triassic units across salt structures and crestal faulting indicate initial salt movement in the eastern Glückstadt Graben and at the Kegnaes Diapir contemporaneous with the onset of Late Triassic regional extension and faulting at the northeastern basin margin. Salt movement continued at least until the early Jurassic. During the Triassic, the Eastholstein Mecklenburg Block formed a more stable area at the transition between the Glückstadt Graben and the fault systems of the northeastern basin margin. Within the Eastholstein Mecklenburg Block, salt movement started only in the latest Triassic and was of decreased intensity. From Middle Jurassic times until the Albian, the North Sea doming event subjected the study area to uplift and erosion, which removed much of the Jurassic and partly Upper Triassic deposits resulting in a study area-wide erosional unconformity.

How to cite: Ahlrichs, N., Noack, V., Seidel, E., and Hübscher, C.: Triassic-Jurassic tectonic evolution of the Baltic sector of the North German Basin: regional extension, salt movement and large-scale uplift, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5173, https://doi.org/10.5194/egusphere-egu22-5173, 2022.

The southwestern margin of Iberian (SWIM) underwent a complex tectonic evolution, related to its proximity to the plate boundary between Africa and Europe, and the Betic-Rif Orogeny. The Algarve, Doñana, Sanlucar and Cadiz Basins developed on the Betics’ foreland since the late Miocene, and their sedimentary infill is composed of deep-water turbiditic, hemipelagic and contourite deposits. This work aims to understand the influence of diapiric structures on the development and evolution of deep-water sedimentation associated with these sedimentary basins. It has been accomplished with the analysis of regional 2D and 3D seismic datasets and a chronological framework from well data.

Extensive diapiric activity was recorded throughout the Late Miocene-Quaternary basins. Salt and shale structures were identified characterized by their internal transparent to chaotic reflections with moderate to low amplitude. Three types of diapirs were observed: i) squeezed, vertical diapiric stocks, ii) vertical elongated diapirs related to compressive deformation, and iii) salt-cored normal faults. Eight diapiric pulses occurred during the late Miocene-Quaternary timeframe. Deep-water sedimentation is influenced by these diapiric pulses in two ways: i) diapiric-related reliefs on the seafloor control down- and along-slope current circulation, and consequently the turbidite and contourite sediment distribution and their deposits architecture, and by ii) changeable accommodation space: depocenter size and capacity for sediment accumulation are variable over time, being directly related to the intensity of the diapiric activity. Contourite deposits also respond to changes in depocenter characteristics by altering drifts geometry and size, from sheeted to mounded to confined, with the increasing intensity of diapiric activity.

This work demonstrates the influence of diapirism in shaping the seafloor paleo-morphology, with diapiric-related reliefs and depocentres, controlling the distribution of deep-water depositional systems. Thus, this study emphasizes the importance of an integrated basin analysis, considering sediment supply, regional tectonics, including diapiric activity, as well as climatic and sea-level variations in controlling deep-water sedimentation.

Acknowledgements: D.D. thanks the Portuguese Foundation for Science and Technology (FCT) for a PhD scholarship (reference SFRH/BD/115962/2016). This research has been conducted under the framework of ‘The Drifters Research Group’, Department of Earth Sciences, Royal Holloway University of London (UK). We thank DGEG (Direção-Geral de Energia e Geologia) and Dr. José Miguel Martins for the supply of the 3D seismic dataset. The bathymetric data used in this work is from the European Marine Observation and Data Network (EMODnet) Bathymetry Project (http://www.emodnet.eu/bathymetry).

How to cite: Duarte, D., Hernández-Molina, F. J., Magalhães, V. H., Roque, C., and Ng, Z. L.: Late Miocene-Quaternary diapiric activity in the SW Iberian Margin: Interaction between salt and shale structures and deep-water sedimentation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11751, https://doi.org/10.5194/egusphere-egu22-11751, 2022.

Welds form due to the tectonically-induced thinning and/or dissolution of salt, with their composition and completeness thought to at least partly reflect their structural position within the salt-tectonic system. Despite their importance as seals or migration pathways for accumulations of hydrocarbons and CO2, we have relatively few examples of drilled subsurface welds; such examples would allow us to improve our understanding of the processes and products of welding, and to test analytical models of the underlying mechanics. In this study we integrate 3D seismic reflection and borehole data from the Green Canyon Area of the northern Gulf of Mexico, USA to characterize the geophysical and geological expression of a tertiary weld, as well as its broader salt-tectonic context. These data show although it appears complete on seismic reflection data, the weld contains c. 38 m of pure halite. This thickness is consistent with the predictions of analytical models, and with observations from other natural examples of subsurface welds. Our observations also support a model whereby compositional fractionation of salt occurs as the salt-tectonic system evolves; in this model, less mobile and/or denser units are typically stranded within the deeper, autochthonous level, trapped in primary welds, or stranded near the basal root of diapirs, whereas less viscous and/or less dense units form the cores of these diapirs and, potentially, genetically related allochthonous sheets and canopies. We also show that shearing of the weld during downslope translation of the overlying minibasin did not lead to complete welding.

How to cite: Evans, S., Alshammasi, T., and Jackson, C.: Salt welding during canopy advance and shortening in the Green Canyon area, northern Gulf of Mexico, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9559, https://doi.org/10.5194/egusphere-egu22-9559, 2022.

Polyphase deformation on passive margins, including fault reactivation, has been documented globally. These processes form complex structures that can be integral to petroleum systems and can provide essential constraints on the kinematic and structural evolution of rifts and passive margins. In some cases, inversion structures can also be used as global markers for far-field stress changes and help us to understand how plate tectonics operates on Earth. Despite the importance of reactivated faults, their identification, extent mapping, controls on kinematic evolution, and knowledge of interaction within fault populations are often poorly constrained. As such, there is need for detailed investigations of such structures, including their relationship with halokinesis, which can lead to complex and sometimes misleading structural observations.

We present a new structural interpretation of the Penobscot 3D seismic reflection survey, and associated relay ramp, imaged offshore Nova Scotia, Canada, down to ~3.5 s TWT, constrained by two exploration wells. The relay ramp comprises two dominant faults that dip approximately SSE and are associated with smaller antithetic and synthetic faults. The wider fault population is dominated by ~ENE-WSW striking normal faults that dip both NNW and SSE. The two major normal faults display evidence for reverse deformation in their lower portions (below ~2.5 s TWT), which manifests as anticlinal folding and reverse offsets. However, in their upper portions the faults display normal offset. Smaller faults tend to only affect the uppermost strata and do not show evidence of reactivation. Analysis of fault throw demonstrates that movement on the two main faults was coupled during both the reverse and normal deformation intervals. Through our structural analysis and previous regional interpretations of widespread salt kinesis, we determine that the observed style of deformation likely occurred due to normal (extensional) reactivation of reverse faults that had initially formed due to halokinesis of underlying salt. The timing of salt movement broadly corresponds to documented times of kinematic reorganisation on many Atlantic margins, and thus salt kinesis may have been in response to this. The kinematic dichotomy with depth along the two dominant faults is important to document as this style of polyphase reactivation may go unrecognised where seismic data does not image the full depth of a structure. Therefore, reactivation may be more widespread than previously thought if only uppermost parts of structures have been imaged. The interpretation of salt as an important contributor to kinematic reactivation of faults is crucial as it likely provides a mechanism to explain inversion at many other locations globally.

How to cite: Peace, A., Schiffer, C., Jess, S., and Phethean, J.: Fault reactivation and halokinesis: an example from the Penobscot 3D seismic volume, offshore Nova Scotia, Canada, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12981, https://doi.org/10.5194/egusphere-egu22-12981, 2022.

Subsurface salt movement is primarily driven by differential loading, which is typically caused by tectonics or sedimentation. During glacial periods, the weight of an ice sheet may represent another source of differential loading. In salt-bearing basins affected by Pleistocene glaciations, however, it often remains unresolved if young deformations at salt structures were triggered by ice loading or represent a continuation of late Cenozoic activity. Numerical modelling can help distinguishing ice-load-induced deformation from halotectonic movement unrelated to salt-ice interaction. A prerequisite for obtaining conclusive model results is the appropriate choice of the rheological behaviours and parameters of the modelled materials.

Finite-element simulations (ABAQUS) were conducted to test and improve existing models of the interaction between salt structures and ice sheets. The models comprise two-dimensional plane-strain sections based on a simplified geological cross-section of a viscoelastic salt structure with elastic overburden and basement rocks. Different parameter sets for the rheology of salt and overburden rocks, including linear versus non-linear viscosity of the salt, were tested to gain insight into the main controlling factors.

All tested configurations show ice load-driven salt flow and deformation of the salt structure and the overburden rocks. The advance of an ice sheet towards the salt structure causes lateral salt flow away from the load into the salt structure and thus uplift at the surface above the salt structure. Complete ice coverage leads to downward displacement of the salt structure and subsidence at the surface. The downward displacement is accompanied by lateral expansion of the salt structure, which is controlled by the elasticity of the overburden rocks. After unloading, the displacements are largely restored by the elasticity of the materials. In all models, the observed deformation was limited to a few metres and no permanent reactivation of salt structures occurred. The deformation is generally larger in models with linear viscous salt than in those applying non-linear viscosity. Considering the low stress caused by a several hundreds of metres thick ice sheet and the time scales of several thousands of years, the application of a linear viscosity appears to be appropriate. The elastic parameters strongly impact the results, with lower Young's moduli leading to larger deformation. Our model results highlight the importance of a careful parameter choice, regarding both the viscous and elastic behaviour of the modelled materials.

How to cite: Lang, J. and Hampel, A.: Ice-load induced salt movement – insights into the controlling parameters from numerical modelling, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1117, https://doi.org/10.5194/egusphere-egu22-1117, 2022.

Growing salt diapirs emerging at the sedimentary surface can produce outflowing salt extrusions, as observed, for instance, in many locations in the Zagros fold-and-thrust belt (Southern Iran). Flow patterns of such salt extrusions are controlled by gravity spreading and gliding. Furthermore, internal structures and shapes of salt extrusions are affected by factors like the local topography, the width of the diapir and the tectonic stress field. Many field examples of outcropping diapirs reveal, however, that the highly soluble evaporites (mainly halite) are already dissolved at the surface and that extrusions are covered by a ‘caprock’ layer, which is built of a multi-compositional residuum of less soluble minerals and rocks. Thickness, composition and mechanical properties of the caprock (density, shear strength, etc.) strongly vary between individual diapirs depending on the original composition of the salt layer, overlying host rock sediments, erosion rate, etc. Hence, the influence of such a caprock on the dynamics of the salt extrusion might also be highly variable and has not yet been investigated. It is unclear, if the caprock deforms by ductile shearing similar as viscous rock salt or if it acts as competent, brittle cover layer deforming by fracturing and brecciation during flow of the underlying salt.

We present a series of 3D analogue experiments and 2D numerical models in which we systematically investigated deformation patterns of the caprock layer during diapiric extrusion of a viscous material. In the analog experiments, we tested different types of granular materials as caprock equivalent to simulate different rheologies. Specifically, a fine-grained powder was used to mimic a competent, high-cohesive rock and a coarse-grained, low-density granulate for a less competent rock. In the numerical models, we tested a wide range of caprock parameters, such as thickness, viscosity, and shear strength. Our study is specifically focused on salt extrusions of the Iranian Zagros fold and thrust belt. Thus, the extrusion patterns in both, analog and numerical models, were tested on 1. passively growing diapirs and 2. diapirs reactivated by lateral shortening.

The results of this modelling study provide insights into the conditions (e.g. minimum thickness or strength) under which a caprock layer has a significant influence on the style of the salt extrusion or only acts as a passive veneer floating on top of the flowing salt. The model results show that a competent or thick caprock forms a polygonal fracture pattern at the beginning of the extrusion, while the separated blocks slide downslope during later stages of the extrusion. An incompetent or thin caprock rather deforms by flow, shear thinning and folding coupled to the flow of the underlying salt. These characteristics can help us to interpret deformation structures observed on natural salt extrusions, in terms of thickness and deformation behavior of the caprock.

How to cite: Warsitzka, M., Słotwinski, M., Krýza, O., and Závada, P.: The deformation of caprock on extruding salt diapirs – insights from analog and numerical modelling, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6980, https://doi.org/10.5194/egusphere-egu22-6980, 2022.

In emergent salt diapirs, the volume of the salt at the surface represents an equilibrium state between the salt supplied from the underlying orifice and that lost by dissolution and erosion at the surface. Therefore, the salt volume at the surface represents the surplus of the salt supply over the dissolution and erosion neglecting any volume changes from the decompaction. Both dissolution and erosion processes occur at or near surface and can be estimated, while estimating salt supply remains challenging because it occurs at depth. At the surface, the salt moves away from the central dome above the diapir’s orifice toward the flanks by gravity spreading in the direction of the slope.

In this work, the salt volume change at the surface was estimated using Persistent Scatterer Interferometry (PSI) data to estimate the salt supply into the surface. While the salt tends to move in the direction of slopes, maximum deformation signal can be detected from the PSI data where the slope direction aligns with the line-of-sight (LOS) of satellite in the east- and west-facing slopes of salt diapirs. The salt deformation was estimated from both the east-west and up-down components of the decomposed PSI data along an east-west trending swath profile across the symmetrical Finu salt diapir to obtain salt gain (surplus) along this profile. During the PSI processing, areas with surface erosion and dissolution (sinkholes) were mostly filtered out, and the relevant salt loss was already accounted when analyzing the salt deformation.  However, the down (subsidence) signal of the analyzed PSI data in nearly horizontal areas in the flanks of the Finu diapir, where salt movement is expected to be horizontal, is assumed to be associated with the subsurface salt dissolution. The used PSI data cover a period of four years from October 2014 to December 2018.

Our results show that salt area surplus is c. 14 m² a^-1 along the profile crossing the Finu diapir. With the profile length of 4.6 km, the surplus rates along it are c. 3.1 mm a^-1. The average subsidence rate on the diapirs flat flanks, which is supposed to be associated with the subsurface dissolution, was estimated at c. 1.0 mm a^-1. Thus, the total supply rate along the profile is c. 4.1 mm a^-1. Along the profile length, these rates mean that a total section area of c. 19 m² a^-1 of salt is added to the profile. Considering the semi-circular and symmetrical shape of the diapir and assuming uniform salt supply rates, the total volume of the salt delivered to the surface is in the order of c. 70,000 m³ a^-1 from the underlying orifice. The orifice is approximately circular with a diameter of c. 1.7 km and an aperture covering c. 2.3 km² area. This means the salt is extruded at a rate of c. 30 mm a^-1 averaged over the period of four years.

How to cite: Zebari, M., Friedrich, A., Plattner, C., Rieger, S., and Parizzi, A.: Quantifying salt extrusion rates in active emergent salt diapirs from Persistent Scatterer Interferometry data and salt budget estimates: Finu Diapir in Zagros (Iran) as a case study, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6470, https://doi.org/10.5194/egusphere-egu22-6470, 2022.