Evaporite Units Research Articles

Messinian salinity crisis record under strong freshwater input in marginal, intermediate, and deep environments: The case of the North Aegean

In the present study, we investigate the Mediterranean–Paratethys connection during the late Miocene in Strymon Basin (North Aegean, northeastern Mediterranean) and compare this onshore sequence with the adjacent offshore Prinos-Nestos sequence, before, during, and after the Messinian Salinity Crisis (MSC). Strymon Basin was a peripheral shallow-water basin during the first MSC stage. The Akropotamos sections expose a clastic sequence with gypsum intercalations, which is dated in the Messinian based on the ostracod and calcareous nannofossil assemblages. This sequence records the Primary Lower Gypsum deposition in a shallow marine environment and its passage via the Messinian erosional surface to a brackish environment with changing salinity conditions similar to the Paratethyan depositional environments. The sequence is capped by a travertine marker horizon observed across the entire Strymon Basin indicating freshwater environment. The Miocene–Pliocene transition is characterized by salinity changes caused by the interaction between Atlantic-Mediterranean and Paratethyan waters, predating the marine reflooding at the end of the MSC, which is attested by the overlying Pliocene open marine deposits. The offshore Prinos-Nestos basin incorporates the Nestos intermediate basin and the Prinos intermediate-deep basin. Borehole and seismic profile data from the offshore Prinos-Nestos oil field reflect a thick clastic sequence, topped by turbidites, and followed by an evaporitic unit deposited during the Messinian. In the Nestos slope area, the evaporite unit consists of anhydrite-shale alternations. Toward the basin's depocenter (Prinos Basin), anhydrite is replaced by halite. The sequence is overlain by Pliocene–Holocene deltaic prograding deposits. Sedimentologic and biostratigraphic data show that the thick halite-shale couplets in the deepest part of the offshore Prinos-Nestos Basin were deposited under permanent marine conditions, suggesting no desiccation before, during, and after the MSC. Conclusively, the present results indicate that a connection between the Mediterranean and the Paratethys was occasionally established before the Pliocene reflooding and favor the non-desiccation MSC model for the deep marine evaporite deposition.

Litho- and biostratigraphy, facies patterns and depositional sequences of the Cenomanian-Turonian deposits in the Ksour Mountains (Saharan Atlas, Algeria)

The Cenomanian-Turonian deposits exposed in the Ksour Mountains, western part of the Saharan Atlas (Algeria), document marine shelf environments that had been thriving on the North African passive margin, connected northwards to the Tethys Ocean, and fringed southwards by the Saharan craton. Their lithological, palaeontological, and sedimentological characteristics have been investigated to provide new insights into the biostratigraphy, palaeo-environmental evolution and sea-level changes in this western part of the Saharan Atlas. Three formations are recognized, from base to top of the studied succession: 1. The El Rhelida Formation comprising two informal units: the mixed siliciclastic-carbonate unit deposited under different flow regime conditions, from shoreline to backshore environments, and the limestone–claystone unit including coastal mudflat deposits prone to storm events. The early Cenomanian age of the El Rhelida Formation is supported by vertebrate assemblages. 2. The Mdaouer Formation comprising two units: the evaporitic unit dominated by claystone and evaporite alternations deposited on a flat coastal sabkha with occasional storms, and the marlstone–limestone unit formed in a peritidal-lagoonal environment. The Mdaouer Formation is of early-middle Cenomanian age. 3. The Rhoundjaïa Formation comprising three units: the lower limestone unit consisting of relatively homogeneous fossiliferous limestones; the middle marly unit composed of marlstone and bioclastic limestones, and the upper limestone unit consisting of carbonates showing vertical variations in faunal content and stratonomy. The Rhoundjaïa Formation was deposited in homoclinal ramp setting. Ammonite data indicate an early late Cenomanian to early Turonian age for this interval. Within an overall transgressive trend, the Cenomanian-Turonian deposits of the Ksour Mountains record three third-order depositional sequences bounded each by regional discontinuities.

Stratigraphy of the Middle Devonian Keg River and Prairie Evaporite formations, northeast Alberta, Canada

Stratigraphy of the Middle Devonian Keg River and Prairie Evaporite formations, northeast Alberta, Canada

Modeling the interaction between presalt seamounts and gravitational failure in salt-bearing passive margins: The Messinian case in the northwestern Mediterranean Basin

The northwest Mediterranean Basin includes a thick Messinian salt sequence composed of three evaporitic units. From these, the intermediate unit, which is dominantly composed of halite, acted as a gravitational detachment favoring the downslope failure of the overlying sediments in a thin-skinned deformation regime. As a result, the structure of the margin is characterized by an upper extensional domain with basinward-dipping listric normal faults and a lower contractional domain that accommodates upslope extension by folding, salt inflation, or diapir squeezing. Lower to middle Miocene volcanic seamounts (presalt reliefs) located at the upper extensional domain locally disrupted the evaporitic units and produced salt flow perturbations. They acted as passive buttresses during the gravitational failure modifying the structural zonation of the margin. Using an experimental approach (sandbox models), we analyze the role played by seamounts during the kinematic evolution of passive margins and how they alter salt flow and suprasalt deformation during gravitational gliding. The experiments found that the seamounts locally interrupt the structural zonation of the margin because they hindered downdip salt flow during early deformation. Seamounts initially compartmentalize the margin architecture, resulting in the development of two gravitational subsystems with two extensional/contractional pairs that are subsequently reconnected when the accumulation of salt analog upslope of the relief is enough to overthrust it. From this point onward, the cover is passively translated downslope as a regional system. The changes in the viscous layer flow velocity related to the dip differences between the flanks and edges of the seamount determine the kinematic evolution of this system. Our experiments also provide geometric constraints to consider during interpretation of these structures, which are commonly poorly imaged in seismic data.

How dry was the Mediterranean during the Messinian salinity crisis?

The Messinian salinity crisis (MSC; 5.97–5.33Ma) is an enigmatic episode of paleoceanographic change, when kilometers-thick evaporite units were deposited in the Mediterranean basin. It is generally accepted that during the MSC interval there was a dry climate in the Mediterranean region. It is difficult to assess how dry the climate was during the MSC because a modern analogue, in size and duration, is absent. Here we reconstruct hydrological changes in the Mediterranean basin during the three main MSC stages using excellently preserved biomarkers. We used the hydrogen isotopic composition of the long chain n-alkanes (δDn-alkanes) to reconstruct the hydrological changes on the land adjacent to the Mediterranean Sea. Additionally, the δD of long-chain alkenones (δDalkenones) is used to observe changes in the Mediterranean Sea water source. The δDn-alkanes recorded during the deposition of Primary Lower Gypsum (stage 1) in Monte Tondo indicate a δD of the precipitation comparable to the present-day Mediterranean implying a similar hydrologic regime (indicated by experiments modelling the Miocene-Pliocene transition). Elevated δDalkenones values from halite unit (stage 2) of the Realmonte mine are associated with kainite and giant polygons, consistent with presumably high evaporative conditions during halite deposition. The δDn-alkanes recorded during the deposition of Upper Gypsum (stage 3) in Eraclea Minoa indicate a δDprecipitation typical for much drier settings, similar to the Red Sea region. The relative contribution of the different alkenones from Eraclea Minoa is similar to the one observed in present-day marine settings suggesting that, during stage 3, connections to the open Ocean were likely maintained. However, the δDalkenones records during deposition of the evaporites in Eraclea Minoa are similar to those synchronously registered in the Black Sea implying that a similar hydrologic regime, characterized by extended drought, covered large areas of southeastern Europe. Based on the δDalkenones similarity and the Paratethys type of ´Lago Mare´ fauna in the Mediterranean we speculate that the surface water during stage 3 was, at times, derived from the Black Sea.

Triassic evaporites of Iberia: Sedimentological and palaeogeographical implications for the western Neotethys evolution during the Middle Triassic–Earliest Jurassic

This paper deals with the Middle Triassic-to-earliest Jurassic evaporite sedimentation in the epicontinental, eastern Iberian platform. This deposition occurred under extensional regime during the westwards migration of the Neotethys Ocean at the start of the Pangea break-up. Although attention is focused on the evaporitic episodes recorded in the Epicontinental (Germanic) Triassic of the platform, the evaporite units in the carbonatic Alpine Triassic are also considered. In the Epicontinental Triassic, up to six evaporitic episodes, which alternated with three carbonatic episodes and a siliciclastic one, occurred between the Anisian and the Lower Hettangian. The evaporitic episodes may be divided into two groups. The stratigraphic units of the older group have similar characteristics in salinity and facies, and were formed in chloride-rich, evaporitic mudflats. In the younger group, the salinity and depositional features display considerable differences and the environments evolved from evaporitic mudflats to extensive salterns. The different evolutive trends in the evaporites of the two groups suggest major re-structuration of the platform after the sedimentation of the siliciclastic units of the middle Keuper (Carnian Humide Episode). Progressive marine influence in the assemblage of the six evaporitic episodes is deduced from the changing nature of the evaporites and their host sediment. All the evaporite units accumulated as transgressive and highstand systems tracts. The close relationship between evaporite units and thick accumulation suggests that the structural control played a major role in the sedimentation. In the Alpine Triassic, the presence of evaporites interbedded in the allochthonous carbonate units is documented. Lateral correlation of the evaporite units of the Epicontinental and the Alpine types of Triassic allows us to reconstruct the facies continuum across the original Iberian platform. Such a west-to-east transect illustrates the palaeogeography, structural evolution, and major depositional controls in the platform during the period under study. The deduced evaporitic pattern could be applied to other Triassic platforms which acted as epeiric seaways for the westward advance of the Neotethys.

Neoproterozoic evaporites and their role in carbon isotope chemostratigraphy (Amadeus Basin, Australia)

The Tonian Bitter Springs Group (∼830–750Ma), within the Amadeus Basin in central Australia consists of thick halite and sulphate evaporite accumulations. The deposition of halite occurred in shallow marine, lagoon (salina) environment (Gillen Formation), and developed into sulphate-dominated supratidal sabkha during sea level regression (Johnnys Creek Formation). The overall regression was interrupted by a transgressive phase lasting at least 20Ma and leading to deposition of basin-wide stromatolitic dolostone (Loves Creek Formation). The salinity and high evaporation is reflected in positive δ13C in carbonates (+4 to +6‰ VPDB) of the evaporitic units, while the shallow marine incursion of the Loves Creek Formation (−2‰ δ13C) show typical marine carbonate isotopic values. The Bitter Springs Group chemostratigraphy has been correlated globally and the negative excursion was named previously after this unit (Bitter Springs Stage anomaly). However, the mechanism of evaporation-driven fractionation of δ13C is different from the commonly proposed inorganic-organic carbon fractionation, and challenges the views on interpreting global chemostratigraphic anomalies or excursion and their cause.Evaporite basins covered vast regions worldwide prior to the Sturtian glaciation, e.g. the Australian evaporites would have covered a third of the continent. The light surface of evaporites and associated carbonates would have had a high albedo and effectively cause less surface heat absorption. This subsequently would have triggered temperature decrease on a continental and possibly global scale. This paper hypothesises that the deposition of evaporites worldwide would have contributed to global cooling starting ∼100Ma prior to Snowball Earth and would have played an important role in global glaciation.

Organic-rich shales from internal Betic basins (SE Spain): potential source rocks analogs for the pre-Messinian Salt play in the Western Mediterranean

Southeastern Spain has a large number of Late Neogene basins with substantial evaporitic deposits that developed under an overall NNW-SSE compressional regime related to the African-European tectonic plates collision. Located in the Betic Cordillera, they can be considered as marginal Mediterranean basins that became gradually isolated during the Tortonian and Early Messinian due to tectonic uplift. Different evaporitic units accumulated in these basins during isolation and, in several cases, evaporitic conditions were associated to episodes of important organic matter accumulation. Results obtained from Late Tortonian to Early Messinian shales collected from boreholes, mines and outcrops in the internal Betic basins of Las Minas de Hellin, Cenajo and Socovos are presented. The organic matter was studied under fluorescence and scanning electron microscopy (SEM), and the main geochemical characteristics defined. They show a relation between organic-rich intervals with high potential of hydrocarbon generation, native sulfur, bio-induced dolomite and evaporitic deposits. These organicrich shales can be found before, during and after the evaporitic episodes. Results from the present study are compared with those previously obtained in the pre-evaporitic deposits of the Lorca Basin that showed high oil generation potential, a restricted-marine origin of the organic matter and a low degree of maturity. The occurrence of such potential source rocks in several basins points to a broad regional distribution. At a larger scale, in the Mediterranean Basin, organic-rich sediments were deposited before and during the Messinian Salinity Crisis. The studied examples could represent analogs for potential source rocks of the pre-Messinian salt play in the Western Mediterranean

Messinian evaporites in the Mesaoria Basin, North Cyprus: facies and environmental interpretations

This study focuses on the depositional environments of the Messinian evaporites exposed in the Mesaoria Basin of Northern Cyprus, which has been considered as a marginal gypsum deposit formed in the upper evaporites. The evaporite unit is divided into several kinds of gypsum facies, such as nodular gypsum (F.1), non-bedded selenite (F.2), bedded selenite (F.3), laminated–interbedded grass-like selenite (F.4), gypsarenite with selenite banks (F.5), gypsum megabreccia (F.6), and non-selenitic laminated gypsum (F.7). Among these, nodular gypsum (F.1) and gypsarenite with thick-bedded selenite banks facies (F.5) occurred on the evaporative shoal, modified by seasonal lowstand–highstand cycles with multiple drying and flooding episodes. Selenite facies (F.2-4) was deposited in a wide range of shallow-subaqueous environments, such as marine-fed salinas divided into deep (perennial), moderately deep and shallow (ephemeral) pans resulted from fluctuations of the pycnocline level in the saline pans. In particular, the shallow pans were temporarily influenced by sheet flood or runoff fresh water, leading to the deposition of the grass-like selenite (F.4) with fresh/brackish water limestone (e.g., Iskele section). The Gypsum megabreccia (F.6) is a mass flow deposit or consists of blocks emplaced by gravity in the deeper basin. This depositional period was indicated by large-scale slope failure and basin margin erosion that was triggered by synsedimentary tectonics towards the end of the Messinian episode. Non-selenitic laminated gypsum beds (F.7) are composed of alternations of resedimented/detrital fine gypsum with (current structures), chemical gypsum cumulates, carbonates and diatomaceous muds (with sulfur nodules). Halite-anhydrite couplets were only inferred in a borehole drilled in Yeri village south of Lefkosa (Nicosia). In contrast to the basin margin erosion between Messinian gypsum and Pliocene marine sediments, the halite-anhydrite grades upwards into the Latest Messinian/Early Pliocene-shelly gray mudstone and peats, presumably indicating Lago-Mare-type deposits. The various kinds of gypsum facies studied here have average values of stable isotopes (δ 87/86Sr = 070896, δ18O = 13.5, and δ 34S = 24.6) which fall into the isotopic range of Messinian marine evaporites.

Sinkholes and caves related to evaporite dissolution in a stratigraphically and structurally complex setting, Fluvia Valley, eastern Spanish Pyrenees. Geological, geomorphological and environmental implications

Evaporite karst and sinkhole development is analysed in a geologically complex area of NE Spain, including four evaporite units with different characteristics and affected by compressional and extensional tectonic structures. The exposed paleosinkholes, including remarkable Early Pleistocene paleontological sites, provide valuable information on the subsidence mechanisms and reveal the significant role played by interstratal karstification in the area. These gravitational deformation structures, including hectometre-scale bending folds and oversteepened normal faults, strongly suggest that the present-day compressional regime inferred in previous studies may be largely based on the analysis of non-tectonic structures. Two gypsum caves ca. 1km long show that passages with restricted cross-sectional area may produce large breccia pipes and sinkholes thanks to the removal of breakdown boulders by high-competence episodic floods. Moreover, the upward progression of cave ceilings by paragenesis and condensation dissolution contributes to increase the probability of sinkhole occurrence. An inventory of 135 sinkholes together with their geological and geomorphological context has been developed. This data base has been used to infer several properties of the sinkholes with practical implications: a magnitude and frequency scaling relationship, spatial distribution patterns, dominant controlling factors and risk implications.

Sulfate–Borate Association (Glauberite–Probertite) In the Emet Basin: Implications For Evaporite Sedimentology (Middle Miocene, Turkey)

Abstract Probertite and glauberite are the main rock-forming minerals in the lacustrine Doganlar succession of the Emet basin. The present paper seeks to characterize and interpret the facies and depositional settings of this mineral association. Probertite is made up largely of microfibers arranged in microbundles, and displays a variety of lithofacies. Many lithofacies show deformation and flowage structures which can be assigned to multistage growth of probertite under synsedimentary conditions. Glauberite displays laminated lithofacies formed by fine-grained clear crystals, and thin- to thick-bedded lithofacies composed of coarser crystals and variable proportions of siliciclastic matrix. Depositional pairs of probertite and glauberite occur at millimeter (laminites), centimeter (alternations), and meter (cycles) scales. Probertite and glauberite are primary products grown subaqueously in a relatively shallow saline lake—either on the bottom (probertite and glauberite) or as cumulate crystals (glauberite)—and interstitially below and close to the bottom. The laminites are made up of microcycles composed of several types of laminae. The microcycles are interpreted as predominantly pluriannual precipitates. In the proposed lake model, the brine body is not deep, as indicated by frequent episodes of subaerial exposure recorded in the succession. This study provides new insight into the genesis of glauberite and probertite, the interpretation of nodular lithofacies, the type of “microfiber evaporites,” the evaporite units made up of sulfate–borate alternations, and the petrographic description of glauberite laminites and their paleoenvironmental interpretation.

Paratacamite from Gypsum Veins in Sandstones of the Kuqa Basin, Xinjiang, China: Implications for a New Epigenetic Cu Enrichment Mechanism

AbstractThe Kuqa Basin filled with Paleogene evaporite series is located in the northeast of the Tarim Basin, Xinjiang, China. It is famous for sandstone‐hosted Cu deposits formed by synsedimentary processes. However, our recent studies reveal that there has been another Cu mineralization mechanism in this basin. Field investigations show that there is a close relationship among faults, salt domes, and brine. Cu deposits are mainly located in two east–west‐trending anticlinal belts in the basin, adjacent to salt domes in the belts. Cu minerals in gypsum veins of the Jidike and Kangcun formations have been investigated by SEM, EDS, and X‐ray diffraction methods. The occurrence of paratacamite in gypsum veins has been reported to coexist with glauberite and halite in the joint planes of sandstones. In addition, it occurs accompanying residual crystal salt encrustation in limestone fractures, or in sandstones in dendritic form. These features indicate that the surface‐Cu enrichment in the Kuqa Basin might have originated from Cu‐bearing brine in the underlying evaporite units, which migrated upward along fractures. In addition, the presence of H2S in the east–west fault belt in the Kuqa Basin, and the discovery of surface sulfur, calcium carbonate, and covellite, suggest thermochemical sulfate reduction near salt domes in the deeper parts of the rock units. This process resulted in the generation of reduced brine and provided a favorable environment for Cu enrichment. Therefore, the surface‐Cu mineralization near salt domes is interpreted to be the result of Cu‐bearing brine migrating upward to the surface along faults (or joints) following the intrusion of deep salt domes. The geological evidence indicates the presence of reducing brine and Cu‐bearing brine near the salt dome in the deeper rocks of the Kuqa Basin, thus making the intrusive contact zone of the salt dome a favorable site for the epigenetic enrichment of Cu. Our study demonstrates that Cu enrichment in the Kuqa Basin resulted not only from synsedimentary deposition but also through epigenetic enrichment associated with salt dome intrusion and brine‐rich fluids.

A record of the Messinian salinity crisis in the eastern Ionian tectonically active domain (Greece, eastern Mediterranean)

AbstractThis integrated study (field observations, micropalaeontology, magnetostratigraphy, geochemistry, borehole data and seismic profiles) of the Messinian–Zanclean deposits on Zakynthos Island (Ionian Sea) focuses on the sedimentary succession recording the pre‐evaporitic phase of the Messinian salinity crisis (MSC) through the re‐establishment of the marine conditions in a transitional area between the eastern and the western Mediterranean. Two intervals are distinguished through the palaeoenvironmental reconstruction of the pre‐evaporitic Messinian in Kalamaki: (a) 6.45–6.122 Ma and (b) 6.122–5.97 Ma. Both the planktonic foraminifer and the fish assemblages indicate a cooling phase punctuated by hypersalinity episodes at around 6.05 Ma. Two evaporite units are recognized and associated with the tectonic evolution of the Kalamaki–Argassi area. The Primary Lower Gypsum (PLG) unit was deposited during the firstMSCstage (5.971–5.60 Ma) in late‐Messinian marginal basins within the pre‐Apulian foreland basin and in the wedge‐top (<300 m) developed over the Ionian zone. During the secondMSCstage (5.60–5.55 Ma), thePLGevaporites were deeply eroded in the forebulge–backbulge and the wedge‐top areas, and supplied the foreland basin's depocentre with gypsum turbidites assigned to the Resedimented Lower Gypsum (RLG) unit. In this study, we propose a simple model for the Neogene–Pliocene continental foreland‐directed migration of the Hellenide thrusting, which explains the palaeogeography of the Zakynthos basin. The diapiric movements of the Ionian Triassic evaporites regulated the configuration and the overall subsidence of the foreland basin and, therefore, theMSCexpression in this area.

Stratigraphy, mineralogy and depositional environment of the evaporite unit in the Aşkale (Erzurum) sub-basin, Eastern Anatolia (Turkey)

The study area is situated in the Aşkale sub-basin where the Early-Middle Miocene aged Aşkale Formation was deposited in a shallow marine to lagoonal environment, and consists of interstratifications of clastic sediments, carbonates and evaporites. The successions of the Aşkale Formation can be divided into four main members interfingering with one another both vertically and laterally, and composed of the sandstone-mudstone-limestone member, the evaporite member, the gravelstone-sandstone-mudstone intercalations and the limestone member. The evaporite unit comprises of secondary gypsum lithofacies formed by hydration of precursor anhydrite, anhydrite, gypsum-bearing limestone and claystone in the form of wedges and lenses. Massive, nodular, nodular-banded, laminated and laminated-banded gpysum lithofacieses in addition to chicken-wire and rare entrolithic structures were described, indicating a sabhka or a shallow water depositional environment. Alabastrine and porphyblastic textures of gypsum were identified within the all lithofacieses with abundant amount of anhydrite relics. Additionally, saponite and illite/smectite, calcite and dolomite, celestite, epsomite were also observed. Successions of the Aşkale Formation were deposited in stable subtropical climatic conditions within rapidly subsiding sub-basin resulted in conversion of sub-basin to shallow platform and even in lagoon environment.

Contrasting Siliciclastic-Evaporite Strata In Subsurface and Outcrop: An Example From the Permian Nippewalla Group of Kansas, U.S.A

Abstract Geologists tend to expect that rocks as they appear in outcrop are a very good approximation of the same strata in the subsurface. But this is not the case in mixed siliciclastic–evaporite units, strata that contain both a siliciclastic and an evaporite mineral component. Distinct differences in lithologic and stratigraphic descriptions of ancient siliciclastic–evaporite strata exist between outcrop and core. These differences present challenges in stratigraphic nomenclature, lithologic correlation, age determinations, and interpretations about past depositional environments, diagenetic history, and paleoclimate. An example of siliciclastic–evaporite strata is the middle Permian to early Triassic gypsum- and/or anhydrite- (hereby referred to as gypsum/anhydrite) and halite-bearing red beds throughout the midcontinent of North America and equivalent strata from other Pangean deposits. Here, we use core and field observations of the middle Permian Nippewalla Group in Kansas to show the range of similarities and differences in lithologies and thicknesses of specific lithofacies in outcrop and at various depths. For example, the displacive halite lithology, consisting of red mudstones dominated by randomly oriented halite crystals, is abundant in cores and interpreted as saline mudflat deposits. The outcrop counterpart is less common, friable, massive red mudstones with some gypsum/anhydrite pseudomorphs after displacive halite crystals. We interpret these lithologic differences of this saline mudflat lithofacies as the result of excellent preservation of buried displacive halite and late-stage dissolution of near-surface halite. Additionally, bedded halite and intergranular halite cements in siltstones and sandstones are also vulnerable to late-stage dissolution near the surface, further modifying lithologies and thicknesses. Thickness of the Nippewalla Group in the Amoco Rebecca K. Bounds core of western Kansas is 931 feet (∼ 284 meters) thick, but it is estimated to be only half as thick in the outcrop belt of south-central Kansas. To estimate amount of rock lost to late-stage dissolution, we conducted dissolution experiments on displacive halite units from cores, which resulted in 60–95% loss of rock thickness and mass due to dissolution of halite. The unconsolidated red sediment resulting from these dissolution experiments compares favorably with much of the fine massive red siliciclastics that make up the greater part of the Nippewalla Group outcrops. We propose that major lithologic differences resulting from near-surface diagenetic processes must be expected in any evaporite-bearing siliciclastic unit. Besides guiding correlation attempts between surface and subsurface, this knowledge is vital for making accurate interpretations of depositional and diagenetic history of siliciclastic–evaporite units.

The deep record of the Messinian salinity crisis: Evidence of a non-desiccated Mediterranean Sea

Abstract This research is focused on a complete reexamination of the evaporite facies present in all the cores that cut through the topmost deposits of the Messinian salinity crisis lying below the floor of the Mediterranean Sea (DSDP Legs 13 and 42A, ODP Legs 107 and 161). This review suggests that the uppermost evaporite units in both western and eastern deep Mediterranean basins consist mainly of clastic (gypsrudite, gypsarenite and gypsiltite) and fully subaqueous deposits (laminar gypsum, selenite and cumulate halite) that are partially affected by burial anhydritization and tectonic-induced recrystallization. No unequivocal evidence of shallow water or even supratidal (sabkha) deposition is in evidence, suggesting that at the very last phase of the salinity crisis the Mediterranean Sea did not experience desiccation, but that deposition took place under permanent subaqueous conditions.

Seismic expression 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 2D/3D seismic data and exploration wells in the central part of the basin, an Upper Jurassic evaporite unit produced numerous salt rollers, salt pillows, reactive, flip-flop, and falling diapirs. Halokinetics began as soon as the early Cretaceous, within just a few million years after the deposition of the Tithonian Sab’atayn evaporite sequence. The significant proportions of nonevaporite lithologies within the “salt” made the seismic interpretation of the salt features challenging. The evaporite sequence had been described by most as a syn-rift unit and therefore a strong correlation was assumed between the subsalt syn-rift basement architecture and the overlying diapirs and other salt-related features. However, seismic reflection and well data revealed a nonsystematic relationship between the salt diapirs and the subsalt basement highs. This observation has very important implications for the subsalt fractured basement play in the Sab’atayn Basin.

Diagenetic evolution of Aptian evaporites in the Namibe Basin (south‐west Angola)

AbstractThe widespread and dissected nature of the Angolan gypsiferous salt residuals offers a uniquely detailed view of the lateral and vertical relations inherent to secondary evaporite textures, which typify exhumed salt masses worldwide. Such secondary textures are sometimes misinterpreted as primary evaporite textures. Thin, metre‐scale and patchy, dome‐like gypsum accumulations are well‐exposed within strongly incised present‐day river valleys along the eastern margin of the Namibe and Benguela basins (south‐west Angola). These sections are time equivalent to the main basinward subsurface evaporites (Aptian Loeme Formation) which mostly consist of halite. The gypsum (here called the Bambata Formation) is interpreted to represent the final residual product of fractional dissolution and recrystallization of the halite mass that occurred during Late Cretaceous margin uplift and continues today. This halite underwent multiple episodes of diagenetic alteration between its deposition and its final exhumation, leading to the formation of various secondary gypsum fabrics and solution‐related karst and breccia textures that typify the current evaporite outcrop. Four different diagenetic gypsum fabrics are defined: thinly bedded alabastrine, nodular alabastrine, displacive selenite rosettes and fibrous satin‐spar gypsum. Current arid conditions are responsible for a thin weathered crust developed at the top of the outcropping gypsum, but the fabrics in the main core of the current at‐surface evaporite unit mostly formed during the telogenetic stage of uplift prior to complete subaerial exposure. Alteration occurred as various dissolving and rehydrating saline minerals encountered shallow aquifers in the active phreatic and vadose zones. Geomorphological and petrographic analyses, mostly based on the cross‐cutting relations and crystallographic patterns in the outcrop, are used to propose a sequence of formation of these different fabrics.

Multiepisodic evaporite sedimentation as an indicator of palaeogeographical evolution in foreland basins (South‐eastern Pyrenean basin, Early–Middle Eocene)

AbstractExtensive deposition of marine evaporites occurred during the Early–Middle Eocene in the South‐eastern Pyrenean basin (north‐east Spain). This study integrates stratigraphic and geochemical analyses of subsurface data (oil wells, seismic profiles and gravity data) together with field surveys to characterize this sedimentation in the foredeep and adjacent platform. Four major evaporite units were identified. The oldest was the Serrat Evaporites unit, with a platform‐slope‐basin configuration. Thick salina and sabkha sulphates accumulated on the platform, whereas resedimented and gravity‐derived sulphates were deposited on the slope, and salt and sulphates were deposited in the deep basin. In the subsequent unit (Vallfogona evaporites), thin sulphates formed on the platform, whereas very thick siliciclastic turbidites accumulated in the foredeep. However, some clastic gypsum coming from the platform (gypsarenites and gypsum olistoliths) was intercalated in these turbidites. The following unit, the Beuda Gypsum Formation developed in a sulphate platform‐basin configuration, where the topography of the depositional surface had become smooth. The youngest unit, the Besalú Gypsum, formed in a shallow setting. This small unit provides the last evidence of marine influence in a residual basin. Sulphur and oxygen isotope compositions are consistent with a marine origin for all evaporites. However, δ34S and δ18O values also suggest that, except for the oldest unit (Serrat Evaporites), there was some sulphate recycling from the older into the younger units. The South‐eastern Pyrenean basin constitutes a fine example of a foreland basin that underwent multiepisodic evaporitic sedimentation. In the basin, depositional factors evolved with time under a structural control. Decreasing complexity is observed in the lithofacies, as well as in the depositional models, together with a diminishing thickness of the evaporite units.

Fault-controlled evaporite deformation in the Levant Basin, Eastern Mediterranean

Abstract During the Messinian Salinity Crisis a multi-layered salt giant of 1.5 km thickness was precipitated in the Levant Basin, easternmost Mediterranean Sea. Incipient deformation of this geologically young salt layer was commonly explained by gravity-driven processes only. Based on high-quality depth-migrated seismic data, we show for the first time, how sub-salt extensional faults influence the internal deformation pattern of the Messinian evaporites in the Levant Basin. Extensional faulting started in the Middle Miocene and lasted until Late Messinian times. We suggest faulting to have caused the development of fault-propagation folds within the evaporite unit. Subsequently, folds may have accommodated tectonic shortening at the Latakia Ridge and evolved into the presently observed complex intra-evaporite fold pattern. While fault-controlled evaporite deformation is evident in the northern part of the Levant Basin only, evaporites are increasingly influenced by Nile-derived differential sediment loading towards the south. Locally, zones of reduced amplitudes in the sub-salt domain terminate into phase-reversed bright spots within the lower part of the evaporites, indicating active fluid migration and potentially evaporite dissolution. Finally, we present a high-resolution velocity model of the Messinian evaporites, based on model-based processing and residual moveout analysis. Relatively high interval velocities of acoustically transparent evaporites (3850–4240 km/s) are consistent with halite, whereas lower velocities of reflective layers (3650–4030 km/s) may point towards the presence of low-velocity evaporite facies like gypsum.