Precise and accurate isotope fractionation factors (α17O, α18O and αD) for water and CaSO4·2H2O (gypsum)

Hałas

BSGF - Earth Sci. Bull.

et al. 2019

Isotopic compositions of water of crystallization and sulfate anionic group in gypsum and polyhalite were used as tracers for events related to their formation and subsequent evolution, as for example origin of crystallization water and extent of thermal overprint. For this purpose, gypsum and polyhalite from the Permo-Triassic evaporites of the Eastern Alps, were analysed for isotope composition of sulfate anionic group (d 34 S and d 18 O SO4 ) and water of crystallization (dD and d 18 O). For comparison, water of crystallisation of polyhalite samples of similar age from New Mexico (USA), Kłodawa (Poland) and Hattberg, Hesse (Germany) were also investigated. Estimated d 18 O and dD values of polyhalite formation brines vary from 14.4 to 3.4‰ and 42.5 to À6.1‰, respectively. Gypsum formation brines show different d 18 O and dD values, from À5.7 to À15‰ and À30.9 to À88.8‰, respectively. The measured d 18 O SO4 values of sulfate group are compatible with a thermal overprint at 100°-200°C for both minerals. The thermal overprint documented for the Eastern Alps led to gypsum but not to polyhalite dehydration. The isotopic composition of water of crystallization suggests that polyhalite is preserving the isotopic signature of an enriched brine. During a subsequent event, anhydrite rehydrated to gypsum, with the isotopic composition of water of crystallisation indicating lower (dD and d 18 O) values than the present-day meteoric water ones. Due to their distinct mineral structure and, as a result, different temperature of dehydratation, gypsum and polyhalite record different histories following precipitation in an evaporative system.

Section: Resultssupporting

confidence: 80%

Section: Resultssupporting

confidence: 80%

Multiple isotope tracers from Permian-Triassic hydrated sulfates: Implications for fluid-mineral interaction

Hałas

BSGF - Earth Sci. Bull.

et al. 2019

Earth and Planetary Science Letters

“…The fractionation factors for oxygen and hydrogen isotopes between the free solution and GHW are largely independent of temperature in the range of most lakes (e.g. 10-35 o C; Gázquez et al, 2017a).…”

Section: Introductionmentioning

confidence: 99%

“…exposure to temperature >50 o C after deposition, solution-reprecipitation, etc.). Whether the original isotopic composition of GHW has been preserved or not must be evaluated on a case-by-case basis (Hodell et al, 2012;Gázquez et al, 2017a).…”

Section: Introductionmentioning

confidence: 99%

Triple oxygen and hydrogen isotopes of gypsum hydration water for quantitative paleo-humidity reconstruction

Gázquez

Morellón

Bauska

et al. 2018

Self Cite

Atmospheric relative humidity (RH) is an important parameter affecting vegetation yet palaeoproxies for RH are scarce and difficult to calibrate. Here we use triple oxygen ( 17 O and  18 O) and hydrogen (D) isotopes of structurally bounded gypsum hydration water (GHW) extracted from lacustrine gypsum to quantify past changes in paleo-atmospheric RH. An evaporation *Manuscript Click here to view linked References isotope mass balance model is used together with Monte Carlo simulations to determine the range of climatological conditions that simultaneously satisfy the stable isotope results of GHW, and with statistically robust estimates of uncertainty. We apply this method to reconstruct the isotopic composition of paleo-waters of Lake Estanya (NE Spain) and changes in atmospheric RH over the last glacial termination and Holocene (from ~15 to 0.6 cal. kyrs BP). The isotopic record indicates the driest conditions occurred during the Younger Dryas (YD; ~12-13 cal. kyrs BP). We estimate a RH of ~40-45% during the YD, which is ~30-35% lower than today. Because of the southward displacement of the Polar Front to ~42 o N, it was both windier and drier during the YD than the Bølling-Allerød period and Holocene. Mean atmospheric moisture gradually increased from the Preboreal to Early Holocene (~11 to 8 cal. kyrs BP, 50-60%), reaching 70-75% RH from ~7.5 cal. kyrs BP until present-day. We demonstrate that combining hydrogen and triple oxygen isotopes in GHW provides a powerful tool for quantitative estimates of past changes in relative humidity.

“…In this scenario, the Afifi brine pool could be largely the result of a glacial lowstand evaporative event, accounting for the agreement between the isotopic composition of its waters and a theoretical evaporation line of Gofiantini et al 51 and the concentration of cations and anions associate to degree of evaporation of seawater by 82-88% 25 . For example, seawater evaporation in pools of a natural salt factory (Cabo de Gata, SE Spain) give similar isotopic values to those found in the Afifi brine pool 58 . However, this hypothesis is inconsistent with the ionic composition of Afifi pool waters, which does not provide evidence of precipitation of sulfates or other minerals.…”

Section: Scientific Reports |mentioning

confidence: 57%

Discovery of Afifi, the shallowest and southernmost brine pool reported in the Red Sea

Duarte

Røstad

Michoud

et al. 2020

Sci Rep

The previously uncharted Afifi brine pool was discovered in the eastern shelf of the southern Red Sea. It is the shallowest brine basin yet reported in the Red Sea (depth range: 353.0 to 400.5 m). It presents a highly saline (228 g/L), thalassohaline, cold (23.3 °C), anoxic brine, inhabited by the bacterial classes KB1, Bacteroidia and Clostridia and the archaeal classes Methanobacteria and Deep Sea Euryarcheota Group. Functional assignments deduced from the taxonomy indicate methanogenesis and sulfur respiration to be important metabolic processes in this environment. The Afifi brine was remarkably enriched in dissolved inorganic carbon due to microbial respiration and in dissolved nitrogen, derived from anammox processes and denitrification, according to high δ 15 N values (+6.88‰, AIR). The Afifi brine show a linear increase in δ 18 O and δD relative to seawater that differs from the others Red Sea brine pools, indicating a non-hydrothermal origin, compatible with enrichment in evaporitic environments. Afifi brine was probably formed by venting of fossil connate waters from the evaporitic sediments beneath the seafloor, with a possible contribution from the dehydration of gypsum to anhydrite. Such origin is unique among the known Red Sea brine pools.Submarine brine pools are bodies of water with elevated salinity that form lake-like structures on the seafloor.