Evaporite Diapirs Research Articles

Utilizing a multi-tracer method to investigate sulphate contamination: Novel insights on hydrogeochemical characteristics of groundwater in intricate karst systems

Karst environments, especially in Mediterranean area, are highly vulnerable to natural and anthropogenic contamination. This study presents a comprehensive hydrogeochemical assesment of surface water and groundwater across a 2300 km2 catchment area spanning Southern Dalmatia (Croatia) and Western Herzegovina (Bosnia and Herzegovina).For the first time in the study area, data were collected over six years integrating ion analysis, sulphur isotope (δ34S) composition, and physical-chemical analysis of water from 30 locations. The research identified four hydrogeochemical facies (carbonate, sulphate, mixed carbonate/sulphate and chloride), influenced by seawater intrusion, carbonate dissolution, evaporite presence, and human activities.Elevated sulphate levels, often exceeding 250 mg/L, were a main focus of the study due to their potential risks to drinking water quality. The study developed a conceptual model to explain the distribution of sulphates, underscoring the importance of evaporite diapirism and δ34S analysis in tracing sulphate origins. These findings contribute to an improved understanding of karst systems and offer essential data for groundwater protection and legislative measures in the Mediterranean region.

The microbial controls on the deposition of Pb‐Zn minerals in carbonate‐hosted Tunisian ore deposits

AbstractThe Ain Allega, Mjar Hannech and Sidi Driss Pb‐Zn‐Ba‐Sr‐As‐(Hg) deposits in northern Tunisia are hosted in a post‐nappe anticline with a core of a Triassic evaporite diapir affected by the NE–SW‐trending Ghardimaou‐Cap Serrat and E‐W lineament. The ore minerals show different styles; particularly, impregnation in dolomite, cement of breccias, replacement ore and open space filling in the dissolution cavities and fractures. Ore minerals include sphalerite, galena, marcasite, pyrite and cinnabar. Principal gangue minerals are composed of barite, celestine, calcite, dolomite and quartz. The orebodies are hosted by Triassic carbonate rocks (Ain Allega ore deposits), Cretaceous carbonate rocks (Mjar Hannech ore deposits) and by the volcanoclastic layers (Sidi Driss ore deposits). These host rocks show hydrothermal alteration, dissolution and brecciation. Sphalerite in the carbonate‐hosted Zn‐Pb deposits in Tunisia occurs as nano‐size microglobular blebs and peloids and forms finely‐laminated bands with wavy and even ripped up features. Peloids are present in collapse breccias of karst cavities. Peloids (5–100 μm) and bacterial filaments (1 μm long) locally form the common micro‐texture of the sulfide mineralization. The core and the shell of peloids are composed of different minerals; there are 1–3 shells and each shell is 1–1.5 μm thick, commonly with coarse crystals. These textures probably represent fossil microbial mats as in‐situ sulfate‐reducing bacteria products and are similar to nano‐textures observed in bacterial biofilms. Electron microscopy, combined with major element changes (Zn, Pb, As, Fe, and Cd) and sulfur isotope values suggest that sphalerite nano‐textures and nano‐spheres are associated with fossilized bacterial‐mat. The δ34S values of sphalerite (−43.9 to +22.38‰) show that the microbial production of H2S controlled sphalerite precipitation. The biogenic nano‐ to macro‐textured sphalerite and sulfur isotope data suggest that microbes had an important role in the genesis of carbonate‐hosted Zn‐Pb deposits in Tunisia during the Miocene.

Interplay of magmatic and diapiric environments in the Djebel El Hamra Pb-Zn-Hg ore district, northern Tunisia

The Djebel El Hamra Pb-Zn-Ba-Sr (Hg) deposits in northern Tunisia are hosted in a post-nappe anticline with a core of a Triassic evaporite diapir affected by the NE–SW-trending Ghardimaou-Cap Serrat lineament. Three stages of mineralization occurred in the Triassic dolostone: stages I and II caused alternating deposition of sulfate (Ba, Sr) and sulfide (sphalerite, galena) minerals; stage III formed late-stage calcite-marcasite-cinnabar. Zebra textures record the syntectonic transition from compression to extension in the Late Tortonian-Messinian interval. Two fluid end-members were involved in sulfate deposition: one low-salinity (L1, ~3 wt% eq. NaCl) fluid, probably from a meteoric origin, and a Na-Ca-Cl brine (L2, ~22 wt% eq. NaCl) solution which originated from the Triassic diapiric source. A third end-member fluid (L3) with long residence time in the basement was also involved in the Pb-Zn deposition. The δ34S values from a cluster of sulfates around +16‰, show a Triassic evaporate source. The sulfur in sphalerite resulted from bacterial sulfate reduction (BSR); however, crystallization in a closed system resulted in a range of δ34S between +1.6 and +26.5‰. The δ34S values in galena (−28.4 to +8.2‰) are consistent with a BSR and thermochemical sulfate reduction (TSR) origin of the sulfur. Secondary ion mass spectrometry (SIMS) lead isotope data in galena (207Pb/204Pb: 15.595 to 16.193, 206Pb/204Pb: 18.673 to 18.939, 208Pb/204Pb: 38.330 to 40.572) point to local contributions (sedimentary and Cenozoic magmatic rocks) to the main source from the Precambrian basement. Ore deposition occurred at a depth of about 2 km at temperatures between 80 and 250 °C. A shallow magmatic heat source was the cause of these thermal fluctuations.

The Genesis of the Salt Diapir-Related Mississippi Valley-Type Ba-Pb-(± Zn) Ore of the Slata District, Tunisia: The Role of Halokinesis, Hydrocarbon Migration, and Alpine Orogenesis

AbstractThe juxtaposition of a Triassic evaporite diapir with the organic matter-rich Fahdene Formation (Albian-Vra-conian) along major faults in the Slata ore district raises the question of the roles played by halokinesis, hydrocarbons, and tectonics in mineralization. The Slata mining district, located in the Tunisian salt diapiric zone, contains Ba-Pb-(± Zn) ore hosted in the Aptian carbonates. The mineralogical paragenetic sequence consists of barite (Ba-1)–galena ± sphalerite ± calcite (Ca-1)–barite (Ba-2) and finally, late calcites (Ca-2 and Ca-3). Fluid inclusions from early barite reveal that it was precipitated from a warm (134°–157°C), H2O-NaCl-KCl-CaCl2, moderately saline (13.3–24.6 wt % NaCl equiv) basinal brine. This fluid is thought to have resulted from the mixing of a deep-seated, hot, metal-bearing fluid with a cooler, dilute SO42−-rich fluid. Early calcite and cogenetic sulfides (galena and sphalerite) precipitated from fluids of similar salinities and temperatures as the barite-forming fluids, but with the additional involvement of hydrocarbons. Sulfur isotope data suggest that thermochemical sulfate reduction of Triassic gypsum was the main source of reduced sulfur for sulfides. Late barite precipitated as a result of the mixing between a Ba-rich, hot, ascending fluid with a cooler, dilute Triassic sulfate-rich fluid in the absence of hydrocarbons. The homogeneous Pb isotope compositions of galena along with the Sr isotope compositions of barite point to a Paleozoic reservoir as the main source of metals with a contribution from the Triassic-Cretaceous rocks. The emplacement of the ore occurred during the Eocene-Miocene Alpine compressional tectonic activity that triggered the circulation of Paleozoic-derived metal-bearing fluids.

Diversity of igneous rocks from the Isachsen Dome, Ellef Ringnes Island, Canadian High Arctic

The sedimentary deposits of the central Sverdrup Basin on Ellef Ringnes Island were affected by both salt diapirism and igneous activity of the Cretaceous High Arctic Large Igneous Province (HALIP). Occurrences of mafic igneous rocks on the centre of salt domes are usually assigned to the Cretaceous magmatism. Petrographic, geochemical, Sr–Nd isotope, and geochronological (Ar–Ar dating) studies on six rock fragments collected on the top of Isachsen Dome reveal a larger variability in the composition and the age compared to HALIP-related rocks from elsewhere on Ellef Ringnes Island. A blocky fragment of tholeiitic hornblende dolerite with an Ar–Ar age of 121 Ma is interpreted to originate from an in-situ intrusion and was uplifted by evaporite diapirism. The other samples are small, sub-rounded pebbles, which represent three different parent rock types. A kaersutite-bearing alkali basalt was possibly formed during the Triassic or Permian. A leucocratic, albitised rock fragment has experienced contact metasomatism at 102 Ma, and three very similar tholeiitic basalt fragments probably derived from the margin of a dyke were auto-hydrothermally affected at 69 Ma. The inferred source area of these exotic pebbles is the segment of the Arctic continental margin in the northeast that was repeatedly affected by igneous events between the Carboniferous and latest Cretaceous and that was uplifted and eroded during the Eocene. The rock fragments were probably deposited as Palaeogene sediments above the rising Isachsen diapir shortly before or as the head of the salt dome has pierced the Earth’s surface. Glacial transport up the top of Isachsen Dome during the Late Wisconsinan glaciation is not very likely due to the contrast between the north to northwest directed ice-flow direction reported in the literature and the assumed northeastern source area of the pebbles; however, it cannot be completely excluded.

Enigmatic massive sulphide mineralization in the High Arctic Large Igneous Province, Nunavut, Canada

Modern mineral exploration strategies should take into account nontraditional metallogenic models for a given geological environment. Here we document the first detailed study of a massive sulphide showing associated with the High Arctic Large Igneous Province (HALIP) and Sverdrup Basin and in fact, only the second example of mineralization described from Axel Heiberg Island, Queen Elizabeth Islands, Canadian Arctic Archipelago. The Between Lake showing (western Axel Heiberg Island) is a small massive sulphide occurrence within scree/talus below a large ridge of gabbro. It was originally described by explorationists as an orthomagmatic sulphide occurrence hosted within a dioritic dyke. New petrographic and mineralogical analyses indicate that the showing consists predominantly of pyrrhotite with lesser pyrite, trace chalcopyrite, and rare sphalerite. No Ni- or Pb-bearing sulphide minerals were detected. Geochemically, the showing contains some Co and Cu, rare Zn, and generally very low Ni contents (<9 ppm). Sulphur isotope ratios of sulphide minerals range from +3.6 to + 6.6‰, somewhat heavier than expected for magmatic-derived S but isotopically lighter than S associated with local evaporite diapirs (+5.8‰ to +12.2‰). Orthomagmatic sulphides hosted in the diorite typically exhibit even lighter isotopic ratios of –3.9‰ to –1.00‰. The data are consistent with potential mafic–siliciclastic volcanogenic massive sulphide mineralization, or the like, the first documented in the HALIP. High heat flow associated with extensive HALIP magmatism was likely the driving force for such mineralization. Mineral prospectivity in Canada’s High Arctic had been predicated upon the potential presence of magmatic Ni – Cu – platinum group element sulphide mineralization. Rather than negating this potential, our findings provide evidence for additional metallogenic potential for this region of Nunavut.

Sediment-hosted Pb–Zn deposits in the Tethyan domain from China to Iran: Characteristics, tectonic setting, and ore controls

The Tethyan domain from China to Iran hosts many important sediment-hosted Pb–Zn deposits but most have been poorly documented. This study summarizes the salient features of these deposits and discusses the type of ore, tectonic setting, and important ore controls, on the basis of new geological observations and previous publications. The Tethyan domain is characterized by the young and extensive Himalayan–Tibetan and Zagros orogens that formed through collisions between the India/Arabia and Eurasia continents since the Late Cretaceous or early Cenozoic. Abundant Mississippi Valley-type (MVT) and subordinate clastic-dominated (CD, also known as SEDEX) Pb–Zn deposits occur in this domain, including in central and eastern Himalayan–Tibetan orogen in China, the Indian passive margin in southern Pakistan, and various tectonic units of Iran. Economically important deposits contain 0.1–21 Mt Pb + Zn and have total metal resources of ∼75 Mt with ∼48% being oxidized ores. All major deposits known in this domain are MVTs (i.e., the Jinding, Huoshaoyun, Mehdiabad, and Angouran deposits).Mississippi Valley-type Pb–Zn deposits occur in continental-collision-related fold-and-thrust belts and forelands, where deposits are mostly located on the margin of the Eurasian continent, with some in the Indian and Arabian continental margins. Clastic-dominated Pb–Zn deposits occur in central Iran and southern Pakistan, hosted by deep-water siliciclastic sequences of the early Cambrian rifted continental margin of Gondwana and the Jurassic passive continental margin of India, respectively. The youngest mineralized rocks and ages constrain that some important MVT deposits (e.g., the Jinding, Chaqupacha, and Angouran deposits) were formed after a main phase of regional compression, during a regional, large-scale strike-slip or crustal-extension stage in a continental collision setting. In sense of lithologic structure, important ore controls for MVT deposits include evaporite diapir structure, carbonate/evaporite dissolution–collapse structure, pre-existing barite, and porous dolostone. Much of the primary sulfide ore in this domain has been oxidized by supergene processes. This is particularly pronounced in the newly discovered Huoshaoyun deposit, where almost all sulfides have been oxidized to smithsonite and cerussite. An understanding of tectonic setting, ore controls, and supergene processes is essential in exploring for MVT deposits in this domain.

Geological setting of the Moorowie Formation, lower Cambrian Hawker Group, Mt Chambers Gorge, eastern Flinders Ranges, South Australia

Geological mapping in 1970 of lower Cambrian outcrop in the eastern Flinders Ranges of South Australia included the description and naming of the Moorowie Formation, representing the uppermost Hawker Group. The mapping is supported by 885 m of measured sections. An early Cambrian regressive-marine shelf-margin succession is described, from the massive Wilkawillina Limestone (base), the grey laminated limestones, syndepositional slump-induced intraformational folds and breccias, collapse talus, and graded sediment gravity flow deposits of the Mernmerna Formation, terrace-edge attrition megabreccias and reefs of the Moorowie Formation, passing up to the red beds of the Billy Creek Formation (top). Rapid changes in sedimentary facies are attributed to basement block movements and diapiric influence on sedimentation with abrupt vertical relief and paleoslope indicated by syndepositional slumping and platform margin collapse. Tuffs in the Mernmerna Formation record contemporaneous volcanism. Massive archaeocyathan limestones, ooid grainstones, peloid limestones, reef-sourced megabreccias and red shales define five members in the overlying Moorowie Formation, signalling shallow-marine regressive conditions and the development of a biologically diverse carbonate platform seaward of evaporitic lagoons and supratidal sabkhas. The megabreccias of the Moorowie Formation formed as thin semi-autochthonous debris aprons or shallow tidal-channel infills resulting from gradual and persistent wave attrition and repeated collapse of a carbonate terrace that was vigorously reworked by tidal currents. Shale interbeds within the Moorowie Formation represent lightly channelised shallow-marine ramp deposits, with adjacent mud flats, as easterly equivalents of the Oraparinna Shale, the earliest of which formed the substrate to the attrition megabreccias. Emergent evaporite diapirs near Mt John and Mt Frome are the probable sources of coarse siliciclastics within the carbonates. Some of the siliciclastics were likely transported onto the carbonate platform by sandstorms or migrating dunes. Late in the Cambro-Ordovician Delamerian Orogeny, earlier salt diapirs at depth were compressed and reactivated as highly mobile evaporite-rubble breccias and intruded as small plugs and dykes into fissures in a lithified and folded cover.The intrusive breccias include metasediment and metabasic xenoclasts attributable to the Callanna Group, while diapir-related faults also host minor copper, lead and barite mineralisation. Documentation of this unique record contributes to wider investigations of the Ediacaran-to-early-Cambrian succession of the Flinders Ranges sector of the Arrowie Basin, adding to its global heritage values, effective management and appreciation by the wider community.

Lateral Facies Variability Along the Margin of an Outcropping Salt-Withdrawal Minibasin, South Australia

Many aspects of depositional processes adjacent to exposed evaporite diapirs arc not well understood, yet these processes are key to understanding sediments that are part of economically important hydrocarbon systems around the world. In the Adelaide Rift Complex of South Australia, diapirs intersected the seafloor and land surface during the Ediacaran-Cambrian at the same time as sediment was being deposited. Excellent exposures of these diapirs and their associated minibasins allow the character and distribution of these deposits to be studied in detail; this study examines the interaction between a diapir body and minibasin sediments from a sedimentological perspective. Numerous sections were measured along the minibasin margin, allowing the sedimentary facies, lateral sediment variability, and depositional processes to be determined. Deposition took place in a variety of environments, ranging from carbonate shelves to subaerially exposed tidal flats and alluvial fans. Minibasin sedimentation adjacent to the diapir is characterized by an abundance of gravity-flow deposits, including turbidites and debrites. These deposits often contain extraformational conglomerates brought to the surface by the diapir and redeposited into the minibasin depocenter. Within the minibasin fill, sedimentary facies are unevenly distributed, and sedimentary character is most affected by the diapir in areas where depositional thinning, onlap, and growth faulting are most common. Comparison of our observations with other localities where salt bodies intersect the surface show that syndepositional salt-sediment interaction results in a recurring set of features that can be useful in predicting the sedimentary character of these deposits. This study is one of relatively few to examine the sedimentology of an outcropping minibasin in detail and to describe lateral variability of sedimentary facies along an outcropping minibasin margin. The deposits discussed here therefore provide a valuable analogue for subsurface and seafloor deposits elsewhere where salt-sediment interactions cannot be studied in detail.

Discriminating between the origins of remotely sensed circular structures: carbonate mounds, diapirs or periclinal folds? Purbeck Limestone Group, Weymouth Bay, UK

Many sedimentary rock successions contain plan-view circular structures, such as impacts, diapirs and carbonate build-ups. When remotely sensed, it can be difficult to discriminate between their formation mechanisms. Here we examine this problem by assessing the origins of circular structures imaged in high-resolution multibeam bathymetric data from Weymouth Bay, UK. The imagery shows 30–150 m across, concave-down structures within the upper Purbeck Limestone Group on the southern limb of the Purbeck Anticline. Similar structures have not been identified in the extensive outcrops around the bay. The morphology and geological setting of the structures are consistent with three different interpretations: carbonate mounds, periclinal folds and evaporite diapirs. However, none of these structures has been previously recorded in the upper Purbeck Limestone Group outcrops of this internationally renowned geological region. We apply a scoring system to 25 features of the circular structures to discriminate between these three alternative interpretations. This analysis indicates that evaporite diapirs are the least likely and carbonate mounds the most likely origin of the structures. The presence of carbonate mounds revises the upper Purbeck palaeofacies distribution in its type area and provides an analogue for the exploration for hydrocarbon reservoirs in lacustrine mounds. Supplementary material: The methods used in this paper and metrics of the circular structures are available at https://doi.org/10.6084/m9.figshare.c.4103840

Remarks on the Messinian evaporites of Zakynthos Island (Io- nian Sea, Eastern Mediterranean).

Detailed mapping of the Neogene deposits on Zakynthos Island shows that the Messinian primary evaporite basins, formed over Ionian basement, are delimited by the westernmost outcrop of the Triassic evaporitic diapirs, located west of the Kalamaki-Argasi Messinian gypsum unit. The post-Miocene external Ionian thrust is emplaced west of the Triassic diapirs. Planktonic foraminifera biostratigraphy indicates that primary evaporite accumulation took place probably during the first stage of the Messinian salinity crisis (5.96-5.60 Ma), in shallower parts of a foreland basin, formed over the Pre-Apulian and the Ionian zone basement. Establishment of these depositional environments, before the Ionian thrust emplacement, was probably due to the particularities of the foreland basin, which extended from the external Ionian to the internal Pre-Apulian zone. Field observations, borehole data and an onshore seismic profile show that the Neogene sediments over the Pre-Apulian basement correspond to the foredeep through forebulge domain of the foreland basin, as it is documented from their spatial thickness distribution. In contrast, the Neogene sediments over the Ionian basement correspond to the wedge top of the foreland basin, which was less subsiding, as it is deduced by their reduced thickness. This lower subsidence rate was the result of the concurrent diapiric movements of the Ionian Triassic evaporites. In Agios Sostis area, located over Pre-Apulian basement, the Neogene sequence is intercalated by decametre-thick resedimented blocks consisting of shallow water selenite. To the southeast, this mass-wasting Messinian gypsum passes to mainly gypsum turbidite. In Kalamaki-Argasi area, located over Ionian basement, the shallow water environment led to the deposition of the observed primary gypsum. Erosion of the primary gypsum of both forebulge and wedge top supplied the foreland basin’s depocenter with gypsum turbidites.

New ideas on the tectonic of the Kurveleshi anticlinal belt in Albania, and the perspective for exploration in its subthrust

Abstract The external thrustbelt of Albania consists of some tectonic zones (Ionian, Kruja and Krasta-Cukali zones), that are westward overthrust, with a large amplitude (50–100 km), above the Apulian platform and South Adriatic Basin. The relative movement of the Adriatico-Apulian sub-plate between, the Euro Asiatic and African plates during from the Mesozoic to the Tertiary period, mainly controlled the tectonic evolution of the Albanides. The Ionian zone consists of anticline belts (Berati, Kurveleshi and Cika), that are overthrust toward the west with an amplitude about 20–30 km Their overthrustings was realized through regional sliding evaporitic horizons, which caused the masking of folded structures in the subthrust, with the perspective plays. The Kurveleshi anticlinal belt represents a mega-anticlinal with a length of 210 km and a width of about 20 km, and it is characterized by anticline structures with heterogeneous dimensions, predominantly those of great dimensions and linear type. The overthrusting of the anticline units has a local character, and it is more developed in the Kurveleshi anticlinal belt. Its magnitude is about 8–10 km. As a result of these overthrusts, imbrication and duplex styles are formed, leadind to the masking of the subthrust complex with structures of large interest (e.g. Delvina, Karbunara, etc.) where two oil fields have been dioscovered beneath the Mali Gjere anticline (Delvina oil field) and the Kremenara anticline (Karbunara oil field). Backthrust faults phenomena are secondary and they taken place in the post-collision stage. Generally they are easterward thrust faults of structural units with an amplitude of 5–10 km. The Kurveleshi anticlinal belt, based on tectonic features, is divided into two parts: The southern part, from Qafa Sevaster in the north down to Greece to the south. and northern part, from Qafa Sevaster in the south up to the end of the Patos-Verbas structure. In the southern part these features predominate: The anticline structures are large in size, and overthrust with a large amplitude (8–10 km) westward. The evaporitic diapirs have erupted through local faults of the anticline structures of the Kurveleshi anticlinal belt (Mali Gjere, Kurveleshi and Fterra anticlines). These eruptions (Delvina, Picar-Kapariel-Bashaj, etc.) have helped in the overthrusting of these structural units. It must be mentioned that the backthrusting is also affected by the diapir action. Moreover, vertical diapir occur, in the center of the structures like Navarica. In the northern part, the anticline structures are generally small to medium in size. Only the Patos-Verbas anticline is larger in size. In the Kurveleshi anticlinal belt the Ballsh and Visoka oilfields have developed. The eastern flank of the Shushica synclinal belt apears folded, and the carbonate anticline structures have developed. Existing oil fields include the Gorisht-Kocul, Cakran-Moallaj-Kreshpan and Amonica. These oil fields shoud continue towards the north (under the overthrust of the Patos-Verbas antcline) and in the south (under the regional ovethrust of the Kuervelesh anticlinal belt).

Exposed evaporite diapirs and minibasins above a canopy in central Sverdrup Basin, Axel Heiberg Island, Arctic Canada

AbstractAxel Heiberg Island (Arctic Archipelago, northern Nunavut, Canada) contains the thickest Mesozoic section in Sverdrup Basin (11 km). The ca. 370‐km‐long island is second only to Iran in its concentration of exposed evaporite diapirs. Forty‐six diapirs of Carboniferous evaporites and associated minibasins are excellently exposed on the island. Regional anticlines, which formed during Paleogene Eurekan orogeny, trend roughly north on a regular ca. 20‐km wavelength and probably detach on autochthonous Carboniferous Otto Fiord Formation evaporites comprising halite overlain by thick anhydrite. In contrast, a 60‐km‐wide area, known as the wall‐and‐basin structure (WABS) province, has bimodal fold trends and irregular (<10 km) wavelengths. Here, crooked, narrow diapirs of superficially gypsified anhydrite crop out in tight anticline cores, which are separated by wider synclinal minibasins. We interpret the WABS province to detach on a shallow, partly exposed canopy of coalesced allochthonous evaporite sheets. Surrounding strata record a salt‐tectonic history spanning the Late Triassic (Norian) to the Paleogene. Stratigraphic thinning against diapirs and spectacular angular unconformities indicate mild regional shortening in which diapiric roof strata were bulged up and flanking strata steepened. This bulging culminated in the Hauterivian, when diapiric evaporites broke out and coalesced to form a canopy. As the inferred canopy was buried, it yielded second‐generation diapirs, which rose between minibasins subsiding into the canopy. Consistent high level emplacement suggests that all exposed diapirs inside the WABS area rose from the canopy. In contrast, diapirs along the WABS margins were sourced in autochthonous salt as first‐generation diapirs. Apart from the large diapir‐flanking unconformities, Jurassic‐Cretaceous depositional evidence of salt tectonics also includes submarine debris flows and boulder conglomerates shed from at least three emergent diapirs. Extreme local relief, tectonic slide blocks, steep talus fans and subaerial debris flows suggest that many WABS diapirs continue to rise today. The Axel Heiberg canopy is one of only three known exposed evaporite canopies, each inferred or known at a different structural level: above the canopy (Axel Heiberg), through the canopy (Great Kavir) and beneath a possible canopy (Sivas).

Sulphate clastic injectites at Sinus Meridiani on Mars

Based on stratigraphic sections, the 1500m-thick sulphate-based “Sinus Meridiani complex” appears to be composed of a superposition of three lithologically similar stratigraphic units, each ending with a residual mesa caprock associated with planation surfaces. The three exposed plains display polygonal fault networks, nodular anydrite/gypsum dykes located along subvertical polygonal fractures, and presumed pipe-like fluid flow structures. Such vertically intrusive fluidized bodies are interpreted as indicative of subsurface evaporite remobilization and injection, which probably occurred near actively rising evaporite diapirs originating from an autochthonous “mother” layer situated underneath the Meridiani region. Renewal of diapirism is inferred to have caused repeated post-depositional cycles of uplift and erosional exhumation during relatively recent times.

Salt tectonics in the Sivas Basin, Turkey: outstanding seismic analogues from outcrops

The Sivas Basin in Central Anatolia is possibly the world’s finest open-air museum of salt tectonics structures. It is an elongated Oligo-Miocene sag basin that developed in an orogenic context above the Neotethys suture zone. A mid-Oligocene quiet period during convergence of the Arabian and Eurasian plates allowed the deposition of a thick sequence of evaporites. Erosion of the Taurus Mountains shed clastic sediments northwards over the evaporitic basin. Sediments and deformation propagated from the south, forming mini-basins and associated evaporite diapirs and walls. Following this quiet period, compression resumed in the early Miocene, enhancing the formation of gypsum overhangs and allochtonous sheets. The Sivas outcrops expose classic salt tectonics geometries associated with the development of diapirs: halokinetic sedimentary sequences along diapir walls, welds and evaporite sheets or canopies, minibasins, and overturned minibasin wings (overturned edges of minibasins). These exposures are some of the finest field analogues for classical petroleum provinces controlled by salt tectonics such as the Gulf of Mexico and offshore Angola. We illustrate seismic-scale structures and, in the vicinity of the evaporite bodies, interesting analogues for drilled structures where seismic data do not provide an image.

Autochthonous versus allochthonous Upper Triassic evaporites in the Sbiba graben, central Tunisia

Two-dimensional seismic data and well data from the Sbiba graben in central Tunisia (North Africa) reveal its asymmetrical structural geometry affected by E–W, N–S, NW–SE, and NE–SW master strike-slip faults. These faults have been intruded by Upper Triassic evaporites, which can be classified into the following three types: (1) sealed evaporite anticlines and domes along folded structures; (2) extrusional wrinkles of “salt walls” at the borders of the graben related to along-strike displacement of the master fault zone; and (3) evaporite outpouring at the center of the graben interpreted as the result of fault and diapir movement. Detailed seismic-stratigraphic analysis highlights a complex interplay between fault growth and evaporite movement, which strongly controlled the evolution of the graben. During the Mesozoic, tectonic stresses induced multidirectional faulting along inherited faults. The vertical rising of the Upper Triassic evaporites was initiated locally at the intersection of master faults during regional extensional and transtensional events in the sub-evaporite basement. The interaction of normal faulting and evaporite diapirism caused lateral outpouring of surface-piercing evaporites. This phenomenon is well expressed in Upper Cretaceous (upper Cenomanian to lower Turonian) strata. The master faults, which cut the diapir at the border and the crest, have caused the extrusion of evaporites. The downward, gravity-driven flow of these evaporites across the slope surface and subsequent accumulation and preservation in Mesozoic sediments is related to the fault escarpment and the adjacent fault-induced depression. There is an apparent relation between tectonic inheritance and inversions of the graben, where interconnected deep faults and diapirs have been reactivated during extensional and contractional tectonic episodes, causing evolution of the structures with the associated sedimentary lapouts. Several autochthonous Triassic evaporites and associated fault escarpments have induced salt canopy structures.

Timing and mechanisms controlling evaporite diapirism on Ellef Ringnes Island, Canadian Arctic Archipelago

ABSTRACTThe Permo‐Carboniferous to Eocene Sverdrup Basin in Canada's Arctic Archipelago is strongly influenced by evaporite diapirism. However, salt structures within the basin have not been extensively investigated recently due to their remote location. This study includes the interpretation of legacy seismic reflection and borehole data to characterize the geometry of selected evaporite domes, and 1D backstripping of wells to investigate tectonic and sedimentary influences on diapirism. Extensional rift‐structures appear to have played a significant role in the formation of evaporite domes by triggering and directing salt movement. Diapirism was initiated by at least the Middle Triassic and continued to develop during the Mesozoic. Differential loading of salt on opposing east–west dome margins led to their present day asymmetric geometries. Diapir growth rates in the Mesozoic were closely linked to the rate of sedimentation and influenced by regional tectonism.

Evidence for subaqueously resedimented sulphate evaporites on Mars

This article documents the clastic nature of sulphate evaporite beds in the Tithonium Chasma located in the Valles Marineris region of Mars. These beds form a stratified succession characterised by very thick interbedded channel-fill breccia bodies. We infer that the bouldery channel-fills were deposited by voluminous mass-flow processes occurring in a relatively deep subaqueous environment. The redeposition of the coarse-grained evaporite would have responded to phases of high denudation rates in rapidly uplifting hinterlands. Tectonic activity also caused the diapiric uprise and exhumation of evaporite diapirs within the Valles Marineris chasmata, where the apparently young and well development karstic landforms probably formed during the late Amazonian age. These new data strongly suggest the deposition of both primary and resedimented evaporites in a marginal basin area, which effectively restricted ocean access through the proposed “proto-Valles Marineris Strait”. The associated ocean may be the “Ocean Borealis” of Late Noachian–Early Hesperian age.

IMPACT OF MAGMATISM ON PETROLEUM SYSTEMS IN THE SVERDRUP BASIN, CANADIAN ARCTIC ISLANDS, NUNAVUT: A NUMERICAL MODELLING STUDY

Numerical modelling is used to investigate for the first time the interactions between a petroleum system and sill intrusion in the NE Sverdrup Basin, Canadian Arctic Archipelago. Although hydrocarbonexploration has been successful in the western Sverdrup Basin, the results in the NE part of thebasin have been disappointing, despite the presence of suitable Mesozoic source rocks, migrationpaths and structural/stratigraphic traps, many involving evaporites. This was explained by (i) theformation of structural traps during basin inversion in the Eocene, after the main phase ofhydrocarbon generation, and/or (ii) the presence of evaporite diapirs locally modifying the geothermalgradient, leading to thermal overmaturity of hydrocarbons. This study is the first attempt at modellingthe intrusion of Cretaceous sills in the east‐central Sverdrup Basin, and to investigate how theymay have affected the petroleum system.A one‐dimensional numerical model, constructed using PetroMod9.0®, investigates the effectsof rifting and magmatic events on the thermal history and on petroleum generation at the DepotPoint L‐24 well, eastern Axel Heiberg Island (79°23′40″N, 85°44′22″W). The thermal history isconstrained by vitrinite reflectance and fission‐track data, and by the tectonic history. The simulationidentifies the time intervals during which hydrocarbons were generated, and illustrates the interplaybetween hydrocarbon production and igneous activity at the time of sill intrusion during the EarlyCretaceous. The comparison of the petroleum and magmatic systems in the context of previouslyproposed models of basin evolution and renewed tectonism was an essential step in the interpretationof the results from the Depot Point L‐24 well.The model results show that an episode of minor renewed rifting and widespread sill intrusionin the Early Cretaceous occurred after hydrocarbon generation ceased at about 220 Ma in theHare Fiord and Van Hauen Formations. We conclude that the generation potential of these deeperformations in the eastern Sverdrup Basin was not likely to have been affected by the intrusion ofmafic sills during the Early Cretaceous. However, the model suggests that in shallower sourcerocks such as the Blaa Mountain Formation, rapid generation of natural gas occurred at 125 Ma, contemporaneous with tectonic rejuvenation and sill intrusion in the east‐central Sverdrup Basin.A sensitivity study shows that the emplacement of sills increased the hydrocarbon generation ratesin the Blaa Mountain Formation, and facilitated the production of gas rather than oil.

Diagenesis and fracturing of Paleocene–Eocene carbonate turbidite systems in the Ionian Basin: The example of the Kelçyra area (Albania)

The Kelçyra area is emplaced in a foreland fold-and-thrust belt (FFTB), characterized by a westward thrusting with the Triassic evaporites as the major décollement level. Several secondary features related with this evolution, like backthrusting, folding, duplex structures, evaporite diapirism are present. During the FFTB evolution, the study area has been subjected to several fracturing events with associated stages of fluid migration. During the pre-deformational stage, complex textures such as crack-and-seal features most likely reflect expulsion of overpressured fluids. These fluids were dominantly host-rock buffered. Within the post-deformational stage, a meteoric fluid caused cementation and development of a karst network during a period of emergence after the thrust emplacement. Subsequently, Mg calcite reprecipitated in the more stable carbonate phase calcite and dolomite, which filled part of the karts network. The latter is finally dedolomitized and locally partially dissolved by a second meteoric fluid flow, which greatly increased the secondary porosity.