Salt Pillows Research Articles

Structural Evolution at the Northeast North German Basin Margin: From Initial Triassic Salt Movement to Late Cretaceous‐Cenozoic Remobilization

AbstractIn this study, we investigate the regional tectonic impact on salt movement at the northeastern margin of the intracontinental North German Basin. We discuss the evolution of salt pillows in the Bay of Mecklenburg in the light of thick‐ and thin‐skinned tectonics, including gravity gliding, and differential loading using seismic imaging. Stratigraphic and structural interpretation of a 170 km long, multichannel seismic line, extending from the Bay of Mecklenburg to northeast of Rügen Island, incorporates well information of nearby onshore wells. This new high‐resolution seismic line completely images the stratigraphic and tectonic pattern of the subsurface, from the base of the Zechstein to the seafloor. Our analysis reveals that subsidence during Late Triassic to Early Cretaceous at the northeastern basin margin was associated with transtensional dextral strike slip movement within the Trans‐European Suture Zone. We reinterpret the Werre and Prerow Fault Zones west of Rügen Island as an inverted, thin‐skinned normal fault system associated with the formation of the Western Pomeranian Fault System. Salt movement in the Bay of Mecklenburg was initiated in the Late Triassic and lasted until the Early Jurassic. A second phase of salt pillow growth occurred during the Coniacian until Cenozoic and correlates with compression‐related regional basin inversion due to the onset of the Africa‐Iberia‐Europe convergence. Thin‐skinned extensional initialization of salt pillow growth and compressional salt remobilization explains salt pillow evolution in the Bay of Mecklenburg. Additionally, we discuss an impact of gravity gliding on salt pillow evolution induced by basin margin tilt.

Mesozoic intraplate deformation in the southern part of the Central European Basin - Results from large-scale 3D modelling

The Central European Basin is an intracontinental basin that initially formed due to long-lasting thermal subsidence accompanied with several tectonic phases of extension during Mesozoic times. Locally, thick evaporites were incorporated in the deformation and led to the formation of detached structures, salt pillows and diapirs. At the end of the Late Cretaceous, the formation of (sub-) basins and (half-) grabens became interrupted by a short-term event of contraction. Especially along the northern and southern edges of the basin, lithospheric shortening resulted in basin inversion and the uplift of large basement blocks. Hence, the present day's structural framework shows a complex pattern of kinematically and chronologically variable structures. Herein, we unravelled these structures for the Altmark region in northern Saxony-Anhalt (Central Germany). We used regional depth maps, reflection seismics and borehole data analysed by use of large-scale subsurface mapping and 3D modelling techniques to completely re-evaluate the structures in the Late Palaeozoic to Cenozoic sedimentary basin succession. Our results show a high variability of tectonic structures: narrow and distributed, in parts reactivated normal fault zones, huge inverted basins, thin-skinned thrust faults, detachment folds and large basement thrusts. The style of deformation significantly changed during the region's evolution. This is indicated by particular structural, kinematic, thermal and rheological conditions, which existed for the individual phases of basin formation and inversion and probably persist until today.

End-Cretaceous Quartz Arenite Formation in an Estuarian Environment under Brine Influence, N. Germany; Linked to both Deccan Volcanism and Chicxulub Impact Degassing during Climate Change

Maastrichtian off-shore carbonate sediments and transitional estuarian quartz arenite (primarily subarkosic/arkosic) deposited in N Germany, underwent indirect effects by end-Cretaceous plume volcanism (Caribbean Arc/Antilles, Amirante Arc/Seychelles, Deccan Traps) and by the Chicxulub impact during climate change. In addition, brines of local salt structures had increasing influence on pore water chemistry of siliciclastics deposited in rim synclines and sub-rosion bowls during the transition from salt pillow state (Upper Campanian/Maastrichtian) to diapirism since the KPgB (66.043 Ma) until end-Paleocene. As main drivers degassing (CO2, SO2 et al.), temperature rise, acid rain/metal toxicity of both volcanic and impact origin caused kill effects by acidification (pH-drop) of sea water resp. dissolution processes on land initiated by complex acid mixtures onto both marine and continental sediments; all in all, leaving a remarkable reduction of the clastics’ primary mineral content, accompanied by kaolinite in-situ neoformation (quartz, kaolinite). Furthermore, driving effects even controlled lithofacies and sequence-analytical patterns (LST, TST, HST). Around the Lower/Upper Maastrichtian B. (MFS) radiolarian ooze was deposited across flat estuarian mouth channels during an ingression (tsunami), originally as soft pebbles, then diagenetically slightly consolidated. Surprisingly, the radiolarian skeletons normally composed of opal or celestite, were identified as β-quartz and elementary silicon. The latter hitherto unknown in nature, demands extreme reducing conditions (in Industries: by elementary A1, Mg, C) in pore water as possibly given by brines (see Atlantis II-Deep, Red Sea). The top portions of the uppermost Maastrichtian deposits of N Germany were eroded by the KPgB-convulsive events. However, recent publications (i.e. from Seymour Island, Antarctica) make evident that Deccan volcanism played obviously a prime role versus the Chicxulub impact during reversal magnetization (Chron 29 R). Thus, there exists a high probability that plume volcanism had important influence on the quartz arenite in-situ formation by degassing and related acid in combination with brines in trap position of the ascending salt diapirs. Accordingly, Price’s concept (2001) major impacting may cause plate motion, has to be modified towards the version plume mechanism and may have the same or even stronger effect, thereby relating to recent studies on the Arabian Platform, Jordan. A synopsis of Phanerozoic loss of biodiversity-events caused by both plume volcanism and impacting comparatively exposes Homo sapiens since the Industrial Revolution as a geological force in biotic as well as abiotic processes in Earth History.

Variability of lithofacial parameters of Lower Jurassic geothermal aquifer in the Malanów region revealed by interpretation of geophysical well logs and seismic data

The Lower Jurassic aquifer is the main target for exploitation of geothermal waters in the Polish Lowlands as it covers over 80% of the area of Poland. Particularly favorable geothermal conditions dominate in the Mogilno-Łodź Trough (central part of the Polish Lowlands), where that aquifer occurs at greatest depth, which results in high temperatures of geothermal waters. The main Lower Jurassic reservoirs in that area are Sinemurian, Pliensbachian, and Upper Toarcian sandstones. These sediments show high lithofacial variability, which results in local changes of hydrogeothermal parameters. Such local variability can be effectively estimated using the seismic data and the interpretation of well logs. Both methods were used for determination of depths to the top surface of Lower Jurassic formation and of distribution of porosity, and clay content, which enabled the researchers to recognize the spatial arrangement of groundwater horizons. The study area is a local structure within the Mogilno-Łodź Trough, in the vicinity of Malanow village. This is a synclinal structure built of Lower Jurassic strata close to the Turek Salt Pillow. Temperature of groundwater in that structure exceeds 80 °C and favorable reservoir parameters ensure relevant discharge. Sandstone horizons show thicknesses over 50 m, low clay contents and porosity around 0.15–0.20.

Deformation of intrasalt competent layers in different modes of salt tectonics

Abstract. Layered evaporite sequences (LESs) comprise interbedded weak layers (halite and, commonly, bittern salts) and strong layers (anhydrite and usually non-evaporite rocks such as carbonates and siliciclastics). This results in a strong rheological stratification, with a range of effective viscosity up to a factor of 105. We focus here on the deformation of competent intrasalt beds in different endmember modes of salt tectonics, even though combinations are common in nature, using a combination of conceptual, numerical, and analog models, and seismic data. In bedding-parallel extension, boudinage of the strong layers forms ruptured stringers, within a halite matrix, that become more isolated with increasing strain. In bedding-parallel shortening, competent layers tend to maintain coherency while forming harmonic, disharmonic, and polyharmonic folds, with the rheological stratification leading to buckling and fold growth by bedding-parallel shear. In differential loading, extension and the resultant stringers dominate beneath suprasalt depocenters, while folded competent beds characterize salt pillows. Finally, in passive diapirs, stringers generated by intrasalt extension are rotated to near vertical and encased in complex folds during upward flow of salt. In all cases, strong layers are progressively removed from areas of salt thinning and increasingly disrupted and folded in areas of salt growth as deformation intensifies. The varying styles of intrasalt deformation impact seismic imaging of LES and associated interpretations. Ruptured stringers are often visible where they have low dips, as in slightly extended salt layers or beneath depocenters, but are poorly imaged in passive diapirs due to steep dips. In contrast, areas of slightly to moderately shortened salt typically have well-imaged, mostly continuous intrasalt reflectors, although seismic coherency decreases as deformation intensifies. Similarly, wells are most likely to penetrate strong layers in contractional structures and salt pillows, less likely in extended salt because they might drill between stringers, and unlikely in tall passive diapirs because the stringers are near vertical. Thus, both seismic and well data may be interpreted to suggest that diapirs and other areas of more intense intrasalt deformation are more halite rich than is actually the case.

Analogue modelling of brittle shear zone propagation across upper crustal morpho-rheological heterogeneities

Crustal shearing of pre-tectonic weak bodies (e.g. salt pillows, igneous pockets) associated with basement strike-slip fault systems is common in nature. Yet the structural pattern arising from the interference between a brittle shear zone and such weak rheological heterogeneities is still not fully explained. In the present work, different sand-box analogue modelling experiments were carried out to better understand, not only the shear zone perturbation effect caused by a strictly rheologic (viscous-weak) anomaly, but also the one arising from a combined morphological perturbation (i.e. traverse topographic crest). Obtained results show that the development of different shear zone deformation patterns is in each case essentially determined by the interplay between: (i) ductile wrenching strain accommodation in the (viscous) weak body; and (ii) coincidence vs. mismatch between main brittle-viscous rheological boundaries and (crest-related) topographic steps. Comparison of the experimentally obtained results with complying natural examples is further discussed, and essentially focused on the NE Atlantic tectono-magmatic interference between the Gloria transform fault and the Tore-Madeira submarine ridge.

Investigating controls on salt movement in extensional settings using finite-element modelling

Salt structures present numerous challenges for targeting reservoirs. Salt movement within the subsurface can follow complex pathways, producing deformation patterns in surrounding strata which are often difficult to decipher. Consequently, the relative role of key salt-flow drivers and geological sensitivities on salt-structure evolution are often poorly understood. To address this, we have developed 2D geomechanical models using the finite-element method to simulate salt diapir and pillow development in two extensional tectonic settings. We conducted model sensitivity analyses to examine the influence of geological parameters on field-scale salt structures and their corresponding deformation pattern. Modelled diapirs developing in thin-skinned extensional settings closely resemble published analogue experiments; however, active and passive stages of diapir growth are seldom or never reached, respectively, thus challenging existing ideas that diapir evolution is dominated by passive growth. In all modelled cases, highly strained domains bound the diapir flanks where extensive small-scale faulting and fracturing can be expected. Asymmetrical diapirs are prone to flank collapse and are observed in models with fast extension or sedimentation rates, thin roof sections or salt layers, or initially short or triangular-shaped diapirs. In modelled thick-skinned extensional settings, salt pillows and suprasalt overburden faults can be laterally offset (decoupled) from a reactivating basement fault. This decoupling increases with increased salt-layer thickness, overburden thickness, sedimentation rate and fault angle, and decreased fault slip rates. Contrary to existing consensus, overburden grounding onto the basement fault scarp does not appear to halt development of salt structures above the footwall basement block. Supplementary material: Animations for all model runs are available at https://doi.org/10.6084/m9.figshare.c.4446272

Salt tectonics and its effect on the structural and sedimentary evolution of the Jeffara Basin, Southern Tunisia

The Jeffara Basin, as part of the North African passive margin, provides a specific type of salt-wall diapirism in Tunisia. A comprehensive study, integrating seismic, gravity, drill wells and surface geological data is performed to model the induced salt geometry and delineate its kinematics. Salt bodies, originated from the Triassic Norian series, are characterized by chaotic seismic response, higher seismic velocity and gravity mass deficit. The architecture of the marine Jeffara Basin results from the complex evolution initiated by Tethyan Ocean rifting.The reconstructed palinspastic sections together with analogic halokinetic models show the successive stages of salt movement and the development of peripheral rim synclines and associated minibasins. Arid climate Triassic developed prolific upper intertidal to supratidal coastal sabkhas bordering the Tethyan Ocean enabled the deposition of thick Triassic salt within the marine Jeffara Basin. During the Early Hettangian extensional phase, associated with the opening of the Tethys Ocean, initiated a series of normal faults. Onlap reflection terminations of Late Hettangian horizons indicate the early Triassic salt rising activity. Large depocenters occurred during Santonian to Eocene; their lateral migration indicates the main active period of salt. Salt pierced the entire sedimentary cover, reached advanced salt diapir stage and set up salt walls during the Cenozoic period. Salt movement mechanism is dictated by the combined effect of tectonism and salt rheology. Salt dynamics controlled the sedimentation and the organization of depositional environments of sediments.Structural interpretation and modeling of the available seismic sections are of critical importance to get a better understating of the evolution of salt structures within the study area. Salt pillows are located at the central part of the basin. To the northeastern part, where thick salts accumulate exhibits the most mature and extended salt-walls. These geometries have an important impact on petroleum exploration.

New insights into salt tectonics in the northern Dutch offshore: a framework for hydrocarbon exploration

Abstract The northern Dutch offshore is an area that has seen less hydrocarbon exploration activity than other areas of The Netherlands. Acquisition of a new regional 3D seismic dataset allowed further testing and re-evaluation of established geological concepts in this area. It is recognized that the presence and movement of Upper Permian Zechstein evaporites had a major impact on depositional patterns in Mesozoic sediments, structural development and hydrocarbon migration. As such, this study looks specifically at the role of salt tectonics in tectonosedimentary development. To assess this salt tectonic evolution within its structural context, a restoration of the Step Graben and Dutch Central Graben was performed. It follows that depositional patterns are closely linked to the nature of salt structure movement and the timing of regional tectonism. For example, during Late Triassic rifting, salt pillows developed and sedimentation focused away from salt structures into depocentres along regional fault trends. Restoration results show that this interplay between salt movement and tectonism is needed to accommodate the sedimentation patterns associated with the formation of the Step Graben and Central Graben during the Triassic and Jurassic, and later during Late Cretaceous and Cenozoic inversion tectonics.

Fault system evolution in the Baltic Sea area west of Rügen, NE Germany

Abstract Based on reprocessed offshore seismic lines acquired during oil and gas exploration in the 1980s, we reconstruct the formation and reactivation of major fault systems in the southern Baltic Sea area since the late Paleozoic. The geological evolution of different crustal blocks from the Caledonian Avalonia–Baltica collision until the Late Cretaceous–Paleogene inversion tectonics is also examined. The detected fault systems occur in the northern part of the Trans-European Suture Zone (TESZ) and belong either to the late Paleozoic Tornquist Fan or to the complex Western Pomeranian Fault System (WPFS) generated during Mesozoic extensional movements. While the NW–SE-trending deep Wiek Fault separates the Arkona High from the Middle Rügen Block, the NNW–SSE-trending Agricola Fault demarcates the Middle Rügen Block to the Falster Block in the west. Together with the Plantagenet Fault and numerous younger faults in the Mesozoic cover, it forms the Agricola Fault System. Furthermore, structural analyses of the Prerow Fault Zone above the Prerow salt pillow and the Werre Fault Zone crossing the Grimmen High indicate a complex fault history.

Structural and microstructural analysis of K–Mg salt layers in the Zechstein 3 of the Veendam Pillow, NE Netherlands: development of a tectonic mélange during salt flow

AbstractIn fully developed evaporite cycles, effective viscosity contrasts of up to five orders of magnitude are possible between different layers, but the structures and mechanics in evaporites with such extreme mechanical stratification are not well understood. The Zechstein 3 unit in the Veendam salt pillow in the Netherlands contains anhydrite, halite, carnallite and bischofite, showing this extreme mechanical stratification. The Veendam Pillow has a complex multiphase salt tectonic history as shown by seismic reflection data: salt withdrawal followed by convergent flow into the salt pillow produced ruptures and folds in the underlying Z3-anhydrite–carbonate stringer and deformed the soft Z3-1b layerWe analysed a unique carnallite- and bischofite-rich drill core from the soft Z3-1b layer by macroscale photography, bulk chemical methods, X-ray diffraction and optical microscopy. Results show high strain in the weaker bischofite- and carnallite-rich layers, with associated dynamic recrystallisation at very low differential stress, completely overprinting the original texture. Stronger layers formed by alternating beds of halite and carnallite show complex recumbent folding on different scales commonly interrupted by sub-horizontal shear zones with brittle deformation, veins and boudinage. We attribute this tectonic fragmentation to be associated with a softening of the complete Z3-1b subunit during its deformation. The result is a tectonic mélange with cm- to 10 m-size blocks with frequent folds and boudinage. We infer that these structures and processes are common in deformed, rheologically strongly stratified evaporites.

Hormuz salt distribution and influence on structural style in NE Saudi Arabia

This study uses previously unpublished reflection seismic data and wells to map part of the western margin of the Hormuz salt basin for the first time, and to link Hormuz facies distribution to the evolution of major structures in NE Saudi Arabia. Most of these major structures host giant or supergiant oil fields in Mesozoic reservoirs. This study is based on seismic interpretation of structural style because the Hormuz occurs at up to 10 km or more depth present day and is not penetrated by any wells. In the eastern part of the study area, seismically transparent zones with structural elements diagnostic of salt tectonics pass laterally into layered seismic facies with local clinoform geometries. The transparent facies are interpreted as mobile salt, the layered facies as immobile evaporite basin-margin strata. The layered facies display onlap and fault-bound relationships with older basement domains, and in map view the boundary between layered and transparent seismic facies at the Hormuz level forms embayments and promontories on the west margin of the salt basin. Areas of mobile salt underlie domal and periclinal structures, such as Karan, Hasbah, Dammam and Khursaniyah. These structures display steeply dipping reflections at depth that can be interpreted as salt pillow flanks, with base salt locally interpretable, and have plan-view aspect ratios of 2 or less. Beyond the limits of layered seismic facies, between the embayments and westwards towards the Arabian Shield, seismic and well data indicate that the major structures are not salt cored, including Berri, Manifa, Safaniya, Jauf, Juraybi'at and Haba.

Structural setting and evolution of the Mensa and Thunder Horse intraslope basins, northern deep-water Gulf of Mexico: A case study

The Mensa and Thunder Horse intraslope minibasins in southcentralMississippi Canyon, northern deep-water Gulf ofMexico, had a linked structural evolution from the Early Cretaceous through the late Miocene. Analysis of the two minibasins illustrates the complexities of deep-water sedimentation and salt tectonics in intraslope minibasins. This study is based on the integration of a 378-mi2 (979-km2) three-dimensional seismic data set,wire-line logs, and biostratigraphic data. These two minibasins comprise several structural features that affected their geologic evolution: basement faults, autochthonous salt, three allochthonous salt systems (top Barremian, top Cretaceous, and Neogene), a growth fault and raft system, three major turtle structures with associated extensive crestal faults, and strike-slip faults. Remnant allochthonous salt pillows are present above the 125 Ma horizon (approximate top Barremian system) and on the 66 Ma horizon (top Cretaceous system) throughout the Mensa minibasin, whereas the top Cretaceous allochthonous salt system is identified regionally by a salt weld in the Thunder Horse area. These allochthonous salt systems formed weld surfaces beneath the Mensa and Thunder Horse turtle structures. Structural features and associated minibasins evolved during several discrete intervals. From the Early Cretaceous through the latest Oligocene (125 to 24 Ma), an extensive allochthonous salt canopy was present within the Mensa and Thunder Horse minibasins. During this interval, sediments loaded the salt, forming thinwedge-and sheet-formdeposits in theMensa area and a thick, northwest-Trending trough in the ThunderHorse area. A secondary allochthonous salt system extruded at the Top Cretaceous level, as seen by remnant salt bodies. Salt withdrawal from these allochthonous salt systems provided accommodation for bowl-and trough-shaped external stratigraphic forms to develop during the Miocene. High sedimentation rates produced salt evacuation from these allochthonous salt systems and initiated diapirism that formed the Neogene allochthonous salt level. The prominent turtle structures in the two minibasins, critical to the formation of traps to the two major fields, developed at slightly different times: Thunder Horse at 14.35 and Mensa at 11.4 Ma. Copyright © 2017 The American Association of Petroleum Geologists. All rights reserved.

Late Cretaceous to recent tectonic evolution of the North German Basin and the transition zone to the Baltic Shield/southwest Baltic Sea

In this study we investigate the Late Cretaceous to recent tectonic evolution of the southwestern Baltic Sea based on a dense grid of seismic reflection profiles. This area covers the Baltic Sea sector of the salt influenced North German Basin and its transition to the salt free Baltic Shield across the Tornquist Zone. The Upper Cretaceous to recent structural evolution is discussed by means of individual seismic sections and derived high-resolution time-structure maps of the main horizons, i.e., the Upper Cretaceous, Tertiary and Pleistocene. The Upper Cretaceous and Tertiary layers reveal numerous significant faults throughout the study area. Several of these faults propagate upwards across the unconsolidated Pleistocene sediments and occasionally penetrate the surface. The salt influenced North German Basin reveals three major fault trends: NW-SE, N-S and NNE-SSW. Several of these faults are located directly above basement (sub-salt) faults and salt pillows. The majority of these faults are trending N-S to NNE-SSW and parallel the direction of the Glückstadt Graben faults. In the salt free Tornquist Zone, we identify two major shallow fault trends, which are NW-SE and NE-SW. The majority of these faults are located above basement faults, following the direction of the Tornquist Zone. We conclude that generally basement tectonics controls activation and trends of shallow faults. If salt is present, the ductile salt layer causes a lateral shift between the sub- and supra-salt faults. Major plate reorganisation related to the Africa-Iberia-Europe convergence and the subsequent Alpine Orogeny caused reactivation of pre-existing faults and vertical salt movement in the Late Cretaceous. The change of stress orientation from NE-SW to a NW-SE during Neogene caused another phase of fault and salt tectonic reactivation. We explain that the ice-sheet loading and/or present-day stress field may have acted in combination, causing the recent tectonics and upward extension of the faults.

Interpretation of gravity and magnetic data with geological constraints for 3D structure of the Thuringian Basin, Germany

We apply a novel method for the separation of potential field sources and their 3D inversion at the regional study area of Thuringian Basin in central Germany. The gravity and magnetic data are separated into long, medium and short wavelengths and then inverted separately. The main goal is to study uniqueness of the solution and its stability in all numerical steps of the interpretation process and to demonstrate, how geological constraints can diminish the degree of non-uniqueness by the interpretation of the gravity and magnetic anomalies. Our numerical experiments with medium wavelengths reveal that if we explain negative anomalies with the topography of near-surface layers, the obtained solution is not supported by borehole data. These negative anomalies are thus explained by restricted bodies (granitic intrusions) at the depths from 4 down to 10km. These bodies are located above a density interface with topography at the depth of approximately 10km. The 3D inversion of magnetic data (at short wavelengths) allows investigating a detailed structure of the upper boundary of the crystalline basement: two uplifts in the depths between 2.0 and 0.7km are found. By using the residual negative anomalies we further study the salt tectonics, showing that the geometry of a salt pillow with a thickness of approximately 200m closely agrees with borehole data.

Megaflaps adjacent to salt diapirs

Megaflaps are steep stratal panels that extend far up the sides of diapirs or their equivalent welds. They have multiple-kilometer fold widths and structural relief and are thus distinct from smaller-scale composite halokinetic sequences. Maximum dips range from near-vertical to completely overturned. Although overturned megaflaps are associated with flaring salt, there is no direct link between megaflap formation and the initiation of salt sheets. Strata within a megaflap are usually convergent, and the lower boundary is typically concordant with the top salt. The upper boundary ranges between a prominent onlap surface and a more diffuse zone of gradual rotation and thinning, and growth strata likewise display both onlap and stacked wedge geometries. We use quantitative cross-section restoration to elucidate the origin and development of megaflaps. Megaflaps typically represent the relatively thin roofs of early salt structures that include single-flap active diapirs, passive diapirs, salt pillows, and salt sheets. They develop during halokinetic drape folding as the minibasin sinks, during contractional squeezing of the diapir and its roof, or during some combination of the two. The kinematics are dominated by either limb rotation or kink-band migration, in which roof strata move through a fold hinge into a lengthening steep megaflap. Both restoration results and direct field evidence suggest that internal strain is minor, with little bed lengthening and thinning. Recognition and understanding of megaflaps are critical to successful petroleum exploration of three-way truncation traps against salt. Megaflaps also have implications for the lateral seal of stratigraphic traps and fluid pressures in minibasins.

Styles of salt tectonics in the Sab’atayn basin, onshore Yemen

A variety of distinct salt tectonic features are present in the Sab’atayn Basin of western Yemen. Based on the interpretation of regional 2D seismic reflection data and exploration wells in the central part of the basin, an Upper Jurassic evaporite formation produced numerous salt rollers, salt pillows, reactive, flip-flop, and falling diapirs. Due to regional extension, halokinetics began as soon as the early Cretaceous, within just a few million years after the deposition of the Tithonian Sab’atayn evaporite sequence, by formation of salt rollers. The salt locally formed salt pillows which evolved to reactive and active salt diapirs and diapiric salt walls as the result of renewed, but low-strain extension in the basin. Some of the diapiric walls further evolved into falling diapirs due to ongoing extension. As the result of a prominent extensional episode at the end of the Cretaceous, many of the diapiric walls in the basin are controlled by large normal faults on their updip flanks. As the post-Cretaceous sedimentary cover is largely missing in the study area, the assumed reactivation of salt structures during the Cenozoic remains poorly constrained. The interpreted changes in the style of salt tectonics in the Sab’atayn Basin offer a better understanding of the regional-scale tectonic development of the Arabian plate during the late Jurassic and Cretaceous.

3D geometric reconstruction of Upper Cretaceous passive diapirs and salt withdrawal basins in the Cotiella Basin (southern Pyrenees)

High-quality images provided by 3D seismic surveys have transformed the interpretations of salt geometries in passive margins. Complementary field studies are needed to expand the ideas derived from seismic image interpretation. The Cotiella Basin exposes middle Coniacian–early Santonian basins developed by post-rift gravity-driven extension and passive diapirism in the proto-Atlantic Ocean. Salt-related sedimentary and structural features were preserved during the subsequent Pyrenean Orogeny, but the diapirs were squeezed to such a degree that they were completely destroyed. As a result, their influence on the development of the Cotiella Basin remains unclear. This paper presents a 3D geometric reconstruction of the extensional faults, the stratigraphic surfaces and the associated salt structures with the main objective of discussing the role of extension versus salt withdrawal. Our results indicate that the main Cotiella Basin was dominated by extensional faulting combined with along-strike salt migration, whereas the smaller Armeña, Mediodía and Seira basins were mainly dominated by salt withdrawal, involving the growth of passive diapirs, salt pillows and transfer faults. This is relevant because the described structures constitute an almost unique example to study in outcrop the structural style and kinematics of structures usually found offshore.

Rising and falling diapirs, shifting depocenters, and flap overturning in the Cretaceous Sopeira and Sant Gervàs subbasins (Ribagorça Basin, southern Pyrenees)

AbstractThe halokinetic structure of inverted salt‐related continental margins is frequently obliterated by compressional overprinting. The Cretaceous Sopeira and Sant Gervàs subbasins of the Ribagorça Basin (south central Pyrenees) show evidence of salt‐related extensional tectonics and diapiric growth along the Iberian Margin of the Mesozoic Pyrenean rift. We present an integrated field‐based tectonic‐sedimentary study to reconstruct the evolution of the Ribagorça Basin system previous to, and in the early stages of, the Pyrenean orogeny. The ~4 km thick Albian‐Cenomanian Sopeira minibasin infill thins toward the basin borders, especially toward the eastern, N‐S trending, Llastarri salt weld. The 90° tilt to the south of the Sopeira basin bottom records the growth of the buried north dipping Sopeira listric fault from Albian to Santonian times, when it evolved as an extensional rollover associated with the Aulet salt roller. The ~3 km thick Cenomanian‐Campanian succession filling the Sant Gervàs flap displays 130° bed fanning attitude from overturned Cenomanian carbonate platform strata to upright Campanian turbidite beds. The Sant Gervàs flap development since Cenomanian times was related to the fall of a large salt pillow after the main Soperia minibasin stage. Jurassic‐Campanian diachronous subsidence is also observed in the adjacent Montiberri, Faiada, and Tamurcia depocenters. Correlation with the Pedraforca, Cotiella, and Basque‐Cantabrian Basins along the southern Pyrenees suggests that a significant segment of the Iberian side of the Pyrenean rift experienced a gravity‐driven extension from Albian to late Santonian. The Ribagorça Basin provides an excellent field analogue for presently buried salt‐related structures of extended passive margins.

Dynamics of prolonged salt movement in the Glückstadt Graben (NW Germany) driven by tectonic and sedimentary processes

The formation of salt structures exerted a major influence on the evolution of subsidence and sedimentation patterns in the Gluckstadt Graben, which is part of the Central European Basin System and comprises a post-Permian sediment thickness of up to 11 km. Driven by regional tectonics and differential loading, large salt diapirs, salt walls and salt pillows developed. The resulting salt flow significantly influenced sediment distribution in the peripheral sinks adjacent to the salt structures and overprinted the regional subsidence patterns. In this study, we investigate the geometric and temporal evolution of salt structures and subsidence patterns in the central Gluckstadt Graben. Along a key geological cross section, the post-Permian strata were sequentially decompacted and restored in order to reconstruct the subsidence history of minibasins between the salt structures. The structural restoration reveals that subsidence of peripheral sinks and salt structure growth were initiated in Early to Middle Triassic time. From the Late Triassic to the Middle Jurassic, salt movement and salt structure growth never ceased, but were faster during periods of crustal extension. Following a phase from Late Jurassic to the end of the early Late Cretaceous, in which minor salt flow occurred, salt movement was renewed, particularly in the marginal parts of the Gluckstadt Graben. Subsidence rates and tectonic subsidence derived from backstripping of 1D profiles reveal that especially the Early Triassic and Middle Keuper times were periods of regional extension. Three specific types of salt structures and adjacent peripheral sinks could be identified: (1) Graben centre salt walls possessing deep secondary peripheral sinks on the sides facing away from the basin centre, (2) platform salt walls, whose main peripheral sinks switched multiple times from one side of the salt wall to the other, and (3) Graben edge pillows, which show only one peripheral sink facing the basin centre.