Recent evaporite deposition associated with microbial mats, Al-Kharrar supratidal–intertidal sabkha, Rabigh area, Red Sea coastal plain of Saudi Arabia

Aref, Mahmoud A.; Taj, Rushdi J.

doi:10.1007/s10347-018-0539-y

Cited by 18 publications

(13 citation statements)

References 49 publications

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“…Only in very arid and hot supratidal environments (sabkha) has anhydrite been reported to form at (near) surface conditions directly from concentrated brines or replacing gypsum (e.g. Kinsman, 1966;Butler, 1969;Butler et al, 1982;Shearman, 1985;Gunatilaka, 1990;Aref and Taj, 2018). More commonly anhydrite appears in evaporitic settings through gypsum dehydration caused by burial to depths below the reaction isotherm (e.g.…”

Section: Earth Surfacementioning

confidence: 99%

Calcium sulfate precipitation pathways in natural and engineered environments

2019

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The solution-mediated formation of calcium sulfate minerals, i.e. gypsum, anhydrite and bassanite, is a common process in both natural and engineered settings. It plays a key role in the global sulfur cycle and serves as an indicator of past environmental conditions on Earth and Mars. Products relying on the crystallization of these minerals have been employed since antiquity, and today they are an essential part of a wide array of industrial applications. Accordingly, the fundamental aspects of calcium sulfate mineralization have been the focus of intensive research during the past century. However, a recent flurry of studies addressing alternative, i.e. nonclassical, nucleation and growth mechanisms has spurred a revisit of the precipitation pathway of the most common phase, gypsum. The newly obtained data sketch a far more complex picture of the mineralization process than previously assumed. This has important consequences for the interpretation of calcium sulfate deposits, both from a geochemical and industrial point of view. In order to shed light on this issue, we discuss in this review both recent and long-standing observations of abiotic formation routes of calcium sulfate minerals as a function of the physicochemical solution properties. By integrating both the classical and non-classical perspectives on crystallization we put forward a unified model for calcium sulfate crystallization. Using this model, we (re)-evaluate the phase stability and transformations taking place in the CaSO 4-H 2 O system. Next, we look into the formation of calcium sulfate minerals occurring in close association with the biosphere. Employing the abiotic case scenario as a benchmarking tool, the possible influence and/or control exerted by biological activity (and its byproducts) on the precipitation pathway is critically reviewed. Finally, we point out the central issues that need to be resolved if we wish to fully understand and control the formation of calcium sulfate solids in natural and engineered environments.

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Section: Earth Surfacementioning

confidence: 99%

Calcium sulfate precipitation pathways in natural and engineered environments

2019

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“…In the same mats, evaporitic crystals, generally abiotic, occur as displacive gypsum lenses, associated with less frequent halite (e.g. Aref & Taj, 2018). In the studied deposits, these evaporitic crystals are generally dissolved but, because the carbonates were lithified early, their indicative shapes are commonly preserved as cavities, later filled with other minerals (pseudomorphs) (Fig.…”

Section: Depositional Modelmentioning

confidence: 86%

“…is also found in modern marginal-marine environments such as the Red Sea (e.g. Aref & Taj, 2018) and is generally representative of sabkha settings (lower sabkha) located both in the continent surrounding salinas and saline pans, and in more marine zones such as coastal sabkhas or tidal flats. In these kinds of environments, within widespread microbial mats, thanks to microbial metabolic activities and environmental conditions (for example, aridity and high salinity), biomediated minerals precipitate, especially carbonates and even silicates (e.g.…”

Section: Depositional Modelmentioning

confidence: 89%

“…Very common, within the CdB, are facies suggesting salina settings, that is shallow perennial saline lakes or very restricted marine-fed lagoons commonly developing laterally to the sabkhas (e.g. Aref & Taj, 2018). In modern systems these kinds of environment persist for long periods of time without drying up, even if they are subjected to dry/wet fluctuations that can change the concentration of the brine and, consequently, the resultant deposits.…”

Section: Depositional Modelmentioning

confidence: 99%

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The onset of the Messinian Salinity Crisis in the central Mediterranean recorded by pre‐salt carbonate/evaporite deposition

et al. 2020

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The Calcare di Base is a carbonate/evaporitic unit formed before the deposition of the massive halite bodies in the main depozones of the Mediterranean region, and has been at the centre of a fiery debate between different 'schools of thought' about its genesis, environmental conditions and timing of deposition. It crops out extensively in Southern Italy, across Neogene basins located on the Tyrrhenian and Ionian margins of northern Calabria, where it was studied through a detailed facies and stratigraphic analysis that revealed the presence of a continental/shallow-marine to slope system, active during the onset of the Messinian Salinity Crisis. During the Calcare di Base deposition, an arid climate regime with intermittent humid phases occurred with a precession forced cyclicity, facing an overall generally cold climatic period. During arid periods, stressed environmental conditions permitted the establishment of widespread microbial-mediated carbonate production, frequently associated with evaporitic (gypsum-dominated) deposition, along a sabkha-type environment with extensive salinas and hypersaline coastal lagoons grading seaward into a carbonate/evaporite shallow-marine shelf. This is testified to by microbial boundstones and dissolution breccias commonly associated with nodular gypsum and arenites affected by desiccation, typically forming metre-scale shallowing-upward peritidal cycles. Seaward, gravity flow deposits are interpreted as re-sedimented shelf limestones, defining a slope apron. Mixed carbonate/evaporite megabreccias and disorganized floatbreccias were deposited along the upper slope, whereas soft deformation with slides, slumps and channelized turbidites further developed along the lower slope to basin. During the humid climate episodes, that affected the platform system with a precession-forced cyclicity, the carbonate production was reduced together with the evaporitic deposition, leading to the widespread deposition of marlstones and fine to coarse siliciclastic deposits.

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“…The occasional occurrence of gypsum is explained by the evaporative pumping mechanism of shallow groundwater. Lenticular gypsum crystals grow diagenetically in the pore spaces of siliciclastic sediments by displacive growth from the fluctuating groundwater (Aref et al, 1997;Aref and Taj, 2018). The chemical composition of the sediments is fundamentally controlled by the source rock composition and secondarily by hydraulic sorting.…”

Section: Discussionmentioning

confidence: 99%