Halite Units Research Articles

Triassic-Early Jurassic evaporites of the Saharan Platform, Algeria: Astronomical and geodynamic constraints on stratigraphy and sedimentation

The sequence stratigraphy of the Late Triassic - Early Jurassic evaporites of the Berkine Basin is described. Disconformities occur between all the major evaporitic units but lack of biostratigraphy (or other) chronostratigraphic control precludes their precise dating. The S4 and S3 Halites are predominantly non-marine halites deposited in low-lying salinas with a barrier to the north. The top of the S4 depositional sequence is marked by the D2, usually regarded as the Tr-J boundary in the Berkine Basin. Both the S3 and S4 salt deposits thin rapidly to the south-east and are thicker in the basin centre coincident with a subcrop of Carnian? aged volcanics. A combination of thermal cooling, rifting and reactivation of N–S lineaments parallel to the Hassi Messaoud-El Biod Arch controlled the (∼1500 m thick) depocenter.Time series analysis shows that astronomical forcing played a key role in the deposition of the S3 and S4 bedded halites. The prevailing climate was monsoonal with major replenishment of the basin indicated by long eccentricity cycles (405 kyr). Sedimentation rates were estimated using eCOCO analysis with average rates of 15 cm/kyr. Well to well comparisons shows that in marginal areas thinner sedimentary sequences relate to slower accumulation rates and periods of non-deposition or deflation. The pattern is similar in the S4 and S3 halite, but the reduced mud content and amalgamation of halite beds suggests a more arid climate in S3 times.The S1+S2 unit marks the first widespread deposition of sulphate in the basin. The lowermost anhydrite beds of the S1 + S2 rest unconformably on the underlying S3 and overstep the basin margins in the south-east; the sequence is capped by the B Horizon a basin-wide carbonate shelf deposit about 25 m thick indicating increased marine influence. Above there is a rapid return to thinly bedded mudstone-halite dominated sedimentation (Lias Salifère) which is overlain by the Lias Anhydritique an alternating sequence of halite and anhydrite deposits. Astronomical parameters of the whole sequence indicate an average sedimentation rate of ∼10 cm/kyr in this marine-influenced section, slower than the halite units. Although the time series analysis cannot provide precision dating of the evaporitic sequences the results indicate that there are important breaks in the depositional record. The combined S4 and S3 halites account for 4.75 Ma and the rest of the Liassic 9.4 Ma. It seems clear that much of the depositional record is missing.These Saharan Platform basins bear much in common with other western Mediterranean evaporite basins. Many show the same overall pattern of sedimentation with increased sulphate deposition above the Tr-J boundary. In late Triassic time they formed a contiguous low-lying zone flanked by cratonic highlands. This zone spanned the Gondwana-Laurussia boundary immediately prior to its break-up and Greater Adria formed a barrier between these basins and the developing Neotethys to the east. The major changes seen in the Saharan Platform are mirrored by the break-up of Adria and the separation of Gondwana and Laurasia and the ultimate connection of the western Mediterranean and the central Atlantic.Although the cyclostratigraphy can tell us much about the absolute duration of sedimentation, the lack of significant anchor points forbids the construction of a detailed chronostratigraphic framework. In particular, the precise location of the Tr-J boundary remains unclear. Although it is usually placed at the base of the D2 Horizon, biostratigraphical evidence from Southern Tunisia places the S3 in the Norian. The sharp contrast between the S4 and S3 halites with the later evaporite sequence suggests that positioning the boundary between the S3 halite and the S1 + S2 unconformity should be given consideration.

Reconstructing lake bottom water temperatures and their seasonal variability in the Dead Sea Basin during MIS5e

AbstractInterglacial periods are characterised by thick accumulations of halite units in the Dead Sea Basin. During these intervals, small water droplets (fluid inclusions, FIs) were entrapped in the halite crystals which serve as windows to estimate the chemistry and physical properties of the primary lake water conditions. Brillouin spectroscopy is used here to reconstruct annual resolution temperatures from a halite core section in the Dead Sea Basin during the onset of Marine Isotope Stage 5e (ca 130 ka) of the Last Interglacial. Lake bottom temperatures can be inferred based on the occurrence of coarse/fine halite facies, as observed today with the formation of equivalent halite facies during winter/summer seasons in the Dead Sea. A recurring increase in lake bottom temperatures is found along the direction of coarse halite layers in three successive years. Moreover, low FI entrapment temperatures were detected in layers of fine (cumulate) halite facies. These results imply a twofold stronger seasonality in the Dead Sea Basin compared to today, with colder winters at the onset of Marine Isotope Stage 5e. The results therefore highlight the potential of using cyclic salt deposits to reconstruct seasonal temperature variability for numerous evaporitic environments in the geological record.

Criteria for the recognition of clastic halite: The modern Dead Sea shoreline

AbstractSedimentological studies of modern halites have focused on shallow water to subaerially‐exposed saline pans, where in‐place crystal growth, dissolution and cementation textures dominate. Clastic halite transported and deposited by waves and unidirectional currents as bedload is poorly known. This paper: (i) describes and interprets the diagnostic sedimentary features of clastic halite from a modern outcrop exposed along the north‐western coastline of the Dead Sea; and (ii) provides criteria for recognition of clastic halite in the rock record. The 2 m thick halite unit at Nahal Og was deposited within the last four decades at water depths <30 m as Dead Sea levels fell ca 30 m. Clastic halites consist of frameworks of sorted crystals with point contacts and no preferred growth fabrics. Halite cumulates, deposited as suspended load, precipitated in the water column and sank to the brine bottom. The excellent sorting and purity of halite crystal layers are unique to cumulates. Small‐scale ripple cross‐stratified thin beds and intraclast conglomerates were deposited from bedload. Halite bedload deposits (composed of halite flat pebbles, ooids, rafts, single clear crystals, cumulate crystals, mud intraclasts and rounded mudballs, foraminifera, gypsum) reflect wave transport and deposition via oscillatory flow above wave base, or by unidirectional flow in the breaker and surf zones. In addition, waves on the Dead Sea coast generate longshore currents. Thin beds produced by wave‐influenced oscillatory transport of halite are symmetrical in cross‐section. Less common cross‐stratified units with asymmetrical cross‐sections indicate unidirectional currents. Clastic halite, especially as a bedload deposit, has rarely been identified in ancient evaporites. Shoreline deposits from ancient halites, however, must contain wave‐reworked and current‐reworked layers and should be common in saline giants, given their enormous size and potential for generating waves and currents. Documentation of modern clastic halite may lead to a better understanding of ancient hypersaline environments on Earth.

Structure of the Tectonic Front of the Western Alps: Control of Fluid Pressure and Halite Occurrence on the Decollement Processes

AbstractThis study focuses on the respective role of (1) the occurrence and the nature of evaporitic layers and (2) the fluid pressure conditions on the decollement processes and the structure of the foreland fold and thrust belt of the Western Alps. The decollement in the Jura Mountains is predominantly localized in halite‐bearing layers. Anhydrite‐bearing units which are not associated to halite are not hosting major decollement. The shift of decollement level between Mid‐Triassic halite unit and Upper Triassic halite unit has induced local tectonic subtractions and, elsewhere, tectonic duplications at depth. Available fluid pressure measurements show that fluids are not overpressured in the Jura. Even below the salt decollement, they remain in hydrostatic conditions. South of the Jura, the absence of halite is correlated with no efficient role of the Triassic layers in terms of decollement. The available pressure measurements show that the decollement is associated with high overpressure. Because of the low friction of halite, the Jura thrust wedge shows a narrow angle (3°–4°). The relatively high friction behavior of the decollement south of the Jura is responsible for stacks of tectonic units associated with a relatively wide angle of the tectonic wedge (12°–13°). The structural change between the Chartreuse and Vercors massifs is not controlled by the properties of the decollement but by the change of thickness of the sedimentary pile involved in the tectonic wedge. The change of thickness is controlled by paleogeographic heritage during Jurassic and Cretaceous times.

Sedimentology and stratigraphy of a modern halite sequence formed under Dead Sea level fall

AbstractHalite sequences in the geological record accumulated in deep hypersaline basins. However, such halite sequences are interpreted based on modern analogues of halite deposition in shallow hypersaline environments. Recently, halite deposition in the deep, hypersaline Dead Sea has been studied together with its coeval environmental and limnogeological forcing. This is the closest modern analogue for deep environments. Therefore, stratigraphy, sedimentology and petrography of a well‐dated, high‐resolution modern Dead Sea halite sequence are explored. The sequence was deposited during a ca 30 m lake‐level decline since the onset of modern halite deposition in 1980, and was compared with sub‐annual lake levels, precipitation and flood records. The sedimentology of the sequence documents the trend of shallowing water depth, including individual floods. The sequence base is composed of alternating bottom growth‐cumulate halite annual couplets, typical of deep hypolimnetic water deposition. Up‐sequence, the annual couplets disappear and towards its top are composed of cumulate layers with dissolution features, typical of shallow epilimnetic water deposition. Halite deposition rate is reduced by 60% at the shallow lakefloor compared with the deep lakefloor, mainly due to the summer undersaturation that leads to depocentre ‘halite focusing'. The top of the sequence contains shoreline deposits, halolites (halite ooids) and polygonal surface cracks, indicating subaerial exposure. This study shows petrographic indicators for summer thermal dissolution (partially dissolved crystals), which are distinct from dissolution features by winter floods that generate a regional truncation surface. Spatial variations in halite thickness and facies, indicating much thinner and spatially limited halite units compared to modelled halite units based on mass balance considerations were also observed. These observations provide criteria for: (i) recognizing water depths and shallowing lake‐level trends from halite sequences throughout the geological record; and (ii) interpreting palaeolimnology, water column structure and the relations between stratigraphic horizons and corresponding shorelines.

RETRACTED: Identification and delineation of potash deposits in Saskatchewan, Canada using pulsed radar technology

Editorial notice: This article has been retracted. See the associated retraction notice here . Saskatchewan, Canada, contains almost half of the world’s known potash deposits, within the Middle Devonian Prairie Evaporite Formation. As the global demand for potash increases, so does the need for faster, greener and cheaper methods of potash identification and extraction. The primary methods for exploration and development of potash include traditional 2D and 3D seismic methods, along with exploration drilling, downhole geophysical logging, coring, and assays for geological interpretation. One challenge with existing seismic geophysical methods in potash exploration is the difficulty in differentiating the responses and interpretation between the evaporite (sylvinite and halite (NaCl)) beds which are intermittently deposited within the Prairie Evaporite Formation. We field tested a new pulsed radar method for subsurface geophysical measurements at the Vanguard Area, Saskatchewan, to demonstrate whether subsurface evaporties could be directly identified non-invasively from ground level. In the Vanguard Area, the Prairie Evaporite Formation occurs at a depth of approximately 1500 m below ground surface (BGS). Achieving deep penetration of the transmitted pulsed radar wave packets, whilst discerning the materials from which the reflected wave packets (containing difference frequency and energy levels) bounced back from, was another scientific challenge. Following robust testing and due diligence on the method, we have been able to confirm that the pulsed radar method is capable of identifying broad lithological zones, differentiating halite units from sylvinite units (the potash-bearing members) within the Prairie Evaporite Formation, and also differentiating individual sub-members within each major potash member. A high-level identification of potash grade (%KCl) of the potash sub-members was also assessed. Based on this preliminary work, the results presented provide significant evidence and resulting confidence in the promise of utilizing the pulsed radar technology for successful identification and delineation of potash deposits

Sedimentology and diagenetic evolution of the Neogene ‘Intermediate Sandstone Unit’ in the halite deposits of the Granada Basin (SE Spain): the turning point in the change from marine to continental sedimentation

The Granada Basin is a small (50 × 50 km) Neogene intramontane basin located in the central part of the Betic Cordillera (Spain). In the latest Tortonian, the Granada Basin desiccated and a thick salt succession formed, encompassing three halite-bearing units: the ‘Lower Halite Unit’, the ‘Intermediate Sandstone Unit’ (ISU), and the ‘Upper Halite Unit’ (UHU). ISU deposits record the onset of marine to non-marine conditions in the Granada Basin. The main purpose of this paper is to study the environment of formation and the diagenetic evolution of the ISU salt-bearing unit, in order to assess the events leading to and resulting from the continentalization of this basin in the late Miocene. This study includes visual core descriptions, petrographic (conventional petrography and scanning electron microscopy), and geochemical (δ34S and δ18O and 87Sr/86Sr) analyses. ISU deposition took place in a coastal lake, isolated from the open sea by a sand barrier. Lake evolution was from a very shallow, hypersaline lacustrine environment to a deeper, perennial lake undergoing frequent storm-induced marine flooding and, finally, to a shallower, perennial saline lake. Isotope analyses point to a mixture of different inflow waters, including marine- and underground (hydrothermal)-water inputs for the origin of the brines. Halite dissolution occurred after flooding events and clear-halite cement was precipitated inside primary-halite dissolution cavities. Early diagenesis involves halite re-crystallisation during repetitive, dissolution–precipitation cycles, gypsum replacement by halite, halite replacement by nodular anhydrite, and framboid pyrite formation. Intermediate- to late-diagenetic processes are silica (megaquartz, chalcedony, and lutecite) replacement of halite and anhydrite, and celestine replacement. Megaquartz formation relates to sulfate-depleted, UHU percolating brines. Chalcedony and lutecite crystallization took place sometime later from sulfate-rich percolating brines, during deposition of the gypsum sequence occurring on top of the salt. Celestine, replacing lutecite, resulted from the interaction with Sr-rich underground waters (via dissolution of previously formed celestine).

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.

Environmental implications of salt facies in the Dead Sea

Thick sequences of salt (halite) have been recovered in a 456-m-long core drilled at the deepest floor of the Dead Sea by the Dead Sea Deep Drilling Project and extending ∼200 k.y. back in time. The salt sequences were precipitated in the ancient lake that occupied the Dead Sea Basin during the last three interglacials during intervals of extreme aridity in the lake’s watershed. The salt layers alternate with “mud” layers that indicate wetter periods in the watershed, when floods transported fine detritus matter to the lake. The salt sources include brine discharge and freshwater runoff that dissolved halite units. Dissolved salts accumulated in the lake during glacials and relatively wet periods when the lake expanded, and precipitated during interglacials when the lake levels dropped. This study establishes for the first time the evaporite facies and sedimentological features of the deep Dead Sea brine during interglacial periods, by using the modern precipitation of halite in the Dead Sea as an analogue for past halite depositional periods as recorded in the drill core. The halite intervals provide a record of facies characterizing a deep-water evaporitic environment. The halite layers consist mainly of two types of crystals: small cumulate crystals containing halite rafts, which indicate precipitation from the surface brine of the lake (epilimnion), and bottom-growth (usually large) halite crystals that precipitated on the lake floor (hypolimnion). The layers of small halite crystals formed during drier periods as compared to the bottom-growth crystals. The bottom-growth halite crystals contain variable quantities of detritus and show mild dissolution structures at the contact between the mud and the halite crystals. These two main types of halite, in combination with “muds” and gypsum, comprise seven categories of salt facies that reflect the hydrological conditions (dry-to-wet), and that display a cyclic (decadal to millennial) pattern along the sampled core intervals. Frequent alternation of these two salt crystal types suggests seasonal changes, whereby the small cumulate crystals were formed during the summer, and the bottom-growth crystals were formed during the winter, when the surface temperatures of the lake were low, and the surface water was less saline and less likely to be saturated with respect to halite. Comparison of the last interglacial halite with the modern halite facies, together with the absence of significant dissolution features within the halite and the cyclic nature of the facies, indicates that the lake was continuously deep (>100 m) during the last 200 k.y.

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.

Controls on basal Zechstein (Wuchiapingian) evaporite deposition in SW Poland

The development of basal Zechstein (Wuchiapingian) strata inSW Polandindicates the existence of a diversified relief inherited after the flooding of the pre-existing depression by the transgressing Zechstein sea. The deeper parts of the basin were the place of development of thin basinal Zechstein Limestone showing sedimentary condensation manifested by bored and encrusted grains and thick evaporites (mostly halite), and in shallow parts Zechstein Limestone reefs followed by thinner evaporite sequences (dominated by anhydrite) occur. The analysis of 3D seismic sections showed that instead of three conventionally recognized evaporite units of stratigraphic potential in the PZ1 cycle, five units occur (from the base to the top: Lower Anhydrite, Lower Oldest Halite, Middle Anhydrite, Upper Oldest Halite, Upper Anhydrite). In a particular place their number may vary from two (Lower Anhydrite at the base of the PZ1 cycle and Upper Anhydrite at the top of the PZ1 cycle) to five. There are two complexes of Lower Anhydrite occurring throughout the platform and basinal zones showing deepening-upward (transgressive) trend. The halite sedimentation in the deepest parts of salt basins began shortly after the deposition of the upper Lower Anhydrite complex while in the sulphate platform areas the sulphate deposition lasted still for a long time. The Lower Oldest Halite deposits occur in the depressions. Between the halite basins, anhydrite platforms occur, and the thickness of anhydrite platform deposits is smaller than it is observed in salt basins. The Upper Oldest Halite in turn is recorded above the anhydrite platform. The two halite units represent different phases of development of halite basins. The Lower Oldest Halite basins are related to the pre-Zechstein depressions, although in some cases their syndepositional subsidence was controlled by reactivation, during the deposition of basal Zechstein strata, of former faults. In turn, the Upper Oldest Halite basins used the accommodation space created due to anhydritization of the Lower Anhydrite deposits composed originally of selenitic gypsum. The 3D seismics evidences that the PZ1 evaporites inSW Polandhave been deposited in far more complex and dynamic system than it was assumed before.

High-resolution strontium isotope stratigraphy of the Messinian deep Mediterranean basins: Implications for marginal to central basins correlation

New 87Sr/86Sr data from DSDP–ODP Messinian cores from deep Mediterranean basins suggest that the usually envisaged correlation of offshore Upper Evaporites with onshore Upper Gypsum deposits of Sicily, Cyprus and Crete recording the stage 3 (5.53–5.33 Ma) of the Messinian salinity crisis may be not entirely correct. High-resolution stratigraphic calibration of Sr isotope data indicates that only a very thin unit (commonly < 50 m) in the uppermost part of the “seismic” Upper Evaporites is characterized by the typically lower values for Sr isotopes with respect to the global Ocean which characterize stage 3 onshore successions (“Lago Mare event”). These deposits mainly consist of interbedded clastic or cumulate gypsum and marls; halite recovered from cores in the Upper Evaporites unit is actually characterized by Sr isotope values consistent with stage 2 deposits of onshore successions. According to these results, the Messinian trilogy of the western Mediterranean basin could be as a whole correlated with the halite unit of the eastern basin, suggesting that different hydrologic conditions characterized the two deep areas during the peak of the salinity crisis.

Salt deposition and brine evolution in the Granada Basin (Late Tortonian, SE Spain)

A group of sedimentary basins in the Betic Chain were formed during the Middle-Late Miocene as a result of the closure of the Tethys during the Alpine orogeny. In the Late Miocene (Tortonian–Messinian) the connections between the Atlantic Ocean and Mediterranean Sea were interrupted and those basins hosted major evaporites. The Granada Basin, an ‘inner basin’ located far from the Mediterranean, contains a thick rock salt deposited during the latest Tortonian in the transition from marine to non-marine conditions. In the centre of the basin, three halite-bearing units overlie a basal anhydrite bed: the Lower Halite Unit, the Intermediate Sandstone Unit and the Upper Halite Unit. Fluid inclusion compositions and bromine concentrations in halite, together with stable isotopes (δ34Ssulfate, δ18Osulfate and 87Sr/86Sr) indicate a mixture of different inflow waters in the Granada Basin, beginning with a marine lagoon that evolved into a salt-pan strongly isolated from the sea. Saline waters evolved from sulfate-rich marine-derived to sulfate-depleted non-marine brines influenced by the addition of CaCl2-rich inputs. These CaCl2-rich waters were probably linked to thermal fluids associated with a major crustal fracture system (Crevillente or Cádiz-Alicante fault system) that cuts through the Granada Basin.

A comprehensive review of the MSC facies and their origins in the offshore Sirt Basin, Libya

Interpretation of 2D long-offset multi-client seismic data acquired by CGGVeritas in 2004–5 has allowed the distribution and composition of the Messinian salinity crisis (MSC) facies to be mapped across the offshore Sirt Basin, Libya. The results reveal that only the Lower and Upper Evaporites are present within the marginal offshore Sirt Basin, with the middle halite unit confined to the deeper basin. The Upper Evaporites, ‘Lago Mare’, are characterized by a period of fluctuating base level and strong water salinity changes controlled by astronomical precession. They consist of interbedded evaporites and clastics with a total of seven precessional cycles recognized, each associated with erosional sub-aerial channels interpreted to have been created by the Eosahabi rivers sourced from the flooding of Neogene Lake Chad. The Lower Evaporites display a high relief, irregular topography which strongly controls the distribution of the overlying Lago Mare facies. They have an overall chaotic high amplitude response with very little internal structure and are interpreted to represent mass transport complex deposits of the Re-sedimented Lower Gypsum unit. There is a strong correlation between the distribution and composition of the MSC facies and the quality of seismic imaging.

CONGOLITE AND TREMBATHITE FROM THE KLODAWA SALT MINE, CENTRAL POLAND: RECORDS OF THE THERMAL HISTORY OF THE PARENTAL SALT DOME

Pseudocubic crystals of (Fe,Mg,Mn) 3 B 7 O 13 Cl borate, ≤ 1.2 mm in size and yellowish through pale-violet to pale-violet-brown and brownish in color, were found in the Klodawa salt dome, located within the Mid-Polish Trough (central Poland), an axial part of the Polish basin belonging to a system of Permian-Mesozoic epicontinental basins of Western and Central Europe. The crystals occur in adjacent parts of the Underlying Halite and Youngest Halite units bordering the Anhydrite Pegmatite unit around the PZ–3/PZ–4 (Leine/Aller) boundary. The internal texture of the crystals reflects phase-transitions from rhombohedral congolite (space-group symmetry R 3 c ) through orthorhombic ericaite ( Pca 2 1 ) to a cubic, high-temperature, mainly Fe-dominant analogue of boracite ( F 43 c ), indicating formation of the phases under increasing temperature. Currently, the parts of the crystals showing orthorhombic and cubic morphology generally represent congolite and, much less frequently, trembathite paramorphs after higher-temperature structural varieties of (Fe,Mg,Mn) 3 B 7 O 13 Cl and (Mg,Fe,Mn) 3 B 7 O 13 Cl, which are unstable at room-temperature. The phase-transitions R 3 c → Pca 2 1 and Pca 2 1 → F 43 c recorded in the morphology of the growing crystals took place at temperatures of 230–250 °C and 310–315 °C, respectively, whereas the total range of (Fe,Mg,Mn) 3 B 7 O 13 Cl borate crystallization was determined to be ca . 100 °C to 350–360 °C. The primary congolite crystallized as a result of the metasomatic reaction of Fe and Mn carriers present within the host rock-salts of the Underlying Halite and Youngest Halite with (BO 3 ) 3− -bearing brines and fluids released from primary evaporate sediments (probably mainly from Upper Younger Halite with potash impurities of the PZ–3 cyclothem) in diagenetic and metamorphic processes induced by disturbances in halokinetic stability, intensive faulting of the pre-Zechstein basement and decompression, and, connected with movements of evaporates, their upward flow in the crust and the formation of a diapiric structure. The phase-transitions R 3 c → Pca 2 1 and Pca 2 1 → F 43 c have been forced by inflows of Mg-bearing fluids sourced from relatively thick loads of potash salts (Younger Potash) of the PZ–3 cyclothem, containing inclusions of carnallite, kainite, and kieserite. The brines and fluids have utilized cracks in Pegmatite Anhydrite as convenient pathways for migration in the dome, in contrast to the host rock-salts, which are too solid to be penetrated by the fluids for distances greater than a few meters.

Large depressions, thickened terraces, and gravitational deformation in the Ebro River valley (Zaragoza area, NE Spain): Evidence of glauberite and halite interstratal karstification

In the studied reach of the Ebro Valley, the terrace and pediment sediments deposited over glauberite- and halite-bearing evaporites show local thickenings (>50m) recording dissolution-induced synsedimentary subsidence. Recent data on the lithostratigraphy of the evaporite sequence allow relating the alluvium thickenings with either halite or glauberite dissolution. The alluvium-filled dissolution basin underlying the youngest terraces (T8–T11) is ascribed to halite karstification; the top of a halite unit approximately 75m thick is situated 40–15m below the valley bottom. The thickenings of terrace (T1–T7) and pediment sediments are attributed to interstratal glauberite karstification: (1) Coincidence between the elevation range of the terraces and that of the glauberite-rich unit. Glauberite beds reach 30 and 100m in single-bed and cumulative thickness, respectively. (2) The exposed bedrock underlying thickened alluvium shows abundant subsidence features indicative of interstratal karstification. The most common structure corresponds to hectometer-scale sag basins with superimposed collapses in the central sector of each basin. The subsided bedrock is frequently transformed into dissolution-collapse breccias showing a complete textural gradation, from crackle packbreccias to chaotic floatbreccias and karstic residues. (3) Paleokarst exposures show evidence of karstification confined to specific beds made up of secondary gypsum after precursory glauberite, partly dissolved and partly replaced. Despite the magnitude of the subsidence recorded by the thickened alluvium and unlike nearby tributaries, the terraces show a continuous and parallel arrangement indicating that the fluvial system was able to counterbalance subsidence by aggradation. A number of kilometer-size flat-bottom depressions have been developed in the valley margin, typically next to and inset into thickened terrace and pediment deposits. The subsidence structures exposed in artificial excavations excavated in the bottom of some depressions and the correlation between the altitudinal distribution of these basins and that of the glauberite-rich unit reveal that subsidence related to interstratal glauberite karstification is the main process involved in their genesis. This research ascribes for the first time the thickenings and deformation of specific terrace levels and pediment levels and the development of large karstic depressions to interstratal karstification of exceptionally thick glauberite units.

Evaluation of halite dissolution at a radioactive waste disposal site, Andrews County, Texas

Waste Control Specialists (WCS) has been granted permits to dispose of radioactive waste at their surface facility in western Andrews County, Texas, U.S.A. The facility is located over Permian-age, halite-bearing formations, and the possibility of dissolution and its effects on the long-term performance of the disposal site must be considered. We compare data from the WCS site and vicinity to three conceptual hydrologic models of dissolution processes (shallow, deep, and stratabound). Geophysical logs yield stratigraphic and lithofacies data from the underlying halite-bearing units, the Permian Rustler and Salado Formations. The halite units are continuous, and thickness and lithofacies vary by depositional process, with no discernible postdepositional dissolution. Modest structural trends in these units differ from local changes in evaporite thickness. Therefore, deformation is not related to thickness differences. Local thickness changes in the middle of the Salado Formation indicate depositional variations. Core obtained from upper evaporite-bearing formations at the WCS site show normal depositional features and no brecciation that would be associated with postdepositional dissolution. Deeply buried bedded halite behaves as a ductile material, and the effective stress is close to zero, so that the pressure in pore fluids approaches lithostatic. Hydraulic gradients are outward from halite toward overlying and underlying rocks, eliminating access for low-salinity fluids. Formation fluids at depth are commonly saline and slow moving, further limiting the dissolution process. The hydrologic systems at the site limit the potential for future dissolution.

A new facies model for the Upper Gypsum of Sicily (Italy): chronological and palaeoenvironmental constraints for the Messinian salinity crisis in the Mediterranean

AbstractThe Upper Gypsum unit of the Caltanissetta Basin (Sicily) records the last phase of the Messinian salinity crisis comprising the so‐called ‘Lago Mare’ event. A new facies analysis study recognizes nine to ten depositional cycles consisting of seven rhythmically interbedded primary gypsum bodies, and two to three sandstone bodies separated by marly terrigenous horizons showing laterally persistent vertical organization. A basal thin gypsum bed is overlain by a cluster of five thicker gypsum bodies. A marly interval containing two distinct sandstone horizons separates this cluster from the overlying uppermost (seventh) gypsum body. The terrigenous Arenazzolo Formation, in turn followed by the lower Pliocene Trubi Formation, is considered here to form the uppermost part of the Upper Gypsum unit. The rhythmic alternation in the sandy marls and gypsum/sandstone bodies records the response of sediments from shelfal to deltaic systems to precession‐driven arid‐wet climate fluctuations causing cyclical changes of both base‐level and water concentration. During wet climate phases (at insolation maxima) marl and sandstone were deposited in a hypohaline environment as suggested by: (i) the typical Lago Mare faunal assemblage and (ii) the negative δ18O values. During arid phases (at insolation minima) the reduced meteoric supply, recorded by higher δ18O values in the carbonate, caused the development of a negative hydrological budget leading to evaporite precipitation. At a basinal scale the Upper Gypsum unit unconformably overlies a mainly clastic evaporite unit containing carbonate breccia (the so‐called ‘Calcare di Base’) and/or clastic gypsum. Towards the basin centres, where the basal contact becomes conformable, a primary gypsum cumulate horizon is present. This layer is interpreted as a possible lateral equivalent of the Halite unit present only in the deepest depocentres. Based on astronomical calibration of the depositional cycles, the Upper Gypsum unit, including the Arenazzolo Formation, spans the interval between 5·33 and 5·53 Ma. This new age calibration allows the deposition of the Halite unit to be dated between 5·6 Ma (top of the Lower Evaporites) and 5·55 Ma (base of the Upper Evaporites) corresponding to isotopic stages TG12 and/or TG14.

Impact of halite dissolution subsidence on Quaternary fluvial terrace development: Case study of the Huerva River, Ebro Basin, NE Spain

This paper analyses the control of evaporite dissolution subsidence on the evolution of the lower 30 km-long reach of the Huerva River up to its confluence with the Ebro River. In the study area the Huerva River flows across different interfingered lithofacies of the subhorizontally lying Ebro Basin fill: (1) shales and sandstones upstream of Cadrete; (2) evaporites dominated by gypsum between Cadrete and Cuarte; (3) gypsum with glauberite and halite units in the subsurface downstream of Cuarte. The halite shows a marked downvalley increase in thickness. Twelve terrace levels and seven pediment levels correlative to some of the terraces have been mapped in the studied area. Upstream of Cadrete, the terrace deposits, with a relatively constant thickness less than 4 m and overlying unsoluble bedrock, remain undeformed. Between Cadrete and Cuarte the deposits of some terraces show local thickening (< 20 m). Downstream of Cuarte, a markedly asymmetric valley carved in gypsiferous bedrock and flanked by a prominent gypsum escarpment changes into a narrower and symmetric valley excavated in the > 60 m-thick terrace alluvium that fills a 5 km-long trough generated by synsedimentary subsidence phenomena caused primarily by the interstratal dissolution of halite. The older terraces (T1 to T4) show slight thickening (> 18 m) and locally truncate paleocollapse structures ascribed to the interstratal karstification of halite beds. The intermediate terraces (T5 to T7) correspond to degradation surfaces that grade downstream of Cuarte into aggradation flights underlain by the abruptly thickened deposits that fill this 5 km-long dissolution trough. Subsidence migrated episodically downstream during the generation of these terraces and the subsidence/aggradation rate was probably large enough to induce a base-level drop and knickpoint migration upstream generating strath terraces with convergent longitudinal profiles. The sedimentological changes that show the thickened terrace deposits in the subsidence area (high proportion of overbank fines (> 60%) including palustrine facies, gravel channels with lower width/depth ratio, multiple fining-upward cycles, decrease in the calibre of the channel gravels) indicate a change in the channel pattern from braided to meandering due to the lowering of the valley slope in the reach affected by subsidence. Some of the anomalous features of the lower terraces (T8 to T12) attributable to dissolution subsidence include: (1) steepening of the T8 terrace profile; (2) change of the T10 terrace from degradational to aggradational downstream Cuarte; and (3) thickening recorded beneath the T11 terrace surface.

Depositional environments of the Mediterranean “Lower Evaporites” of the Messinian salinity crisis: Constraints from quantitative analyses

We use simple quantitative analyses to evaluate controversial water level scenarios for the Mediterranean “Lower Evaporites” of the Messinian salinity crisis. Our results indicate that a shallow-water scenario for the Lower Gypsum units – with Mediterranean water level lower than the sill at Gibraltar – would imply unrealistic salt thicknesses on the order of 3 km. Some outflow to the open ocean must have persisted, implying that the Mediterranean was a deep-water basin during Lower Gypsum formation. Since glacio-eustatic fluctuations do not seem to have had a major influence on Lower Gypsum deposits, Mediterranean water level was even substantially higher than the Gibraltar sill. Our analyses furthermore show that precessional changes in the freshwater budget may explain the observed cyclic lithological changes of gypsum and non-evaporitic sediments. Potential precipitation of gypsum in the deep Mediterranean basins would have critically depended on the availability of oxygen and thus on the stratification of the water column. Finally, our results indicate that the deep Mediterranean halite units could have been deposited under shallow conditions, assuming that they correspond to the ~ 70 kyr time interval between glacials TG12 and TG14, when Mediterranean outflow to the Atlantic was blocked.