Experimental investigation of Ca isotopic fractionation during abiotic gypsum precipitation

Harouaka, Khadouja; Eisenhauer, Anton; Fantle, Matthew S.

doi:10.1016/j.gca.2013.12.004

Cited by 42 publications

(17 citation statements)

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“…The gypsum crystals are offset from the fluids by 1.0‰-1.3‰, with larger apparent offsets occurring with the most extreme isotopic enrichments. This fractionation may be dependent on additional factors such as temperature, precipitation rate, and crystal morphology (Harouaka et al, 2014), but the steady enrichment of the fluid suggests an apparent average fractionation of ~1.0‰. These experiments neglect the dynamic balance of evaporation and recharge of geological basins, but facies changes in evaporite sequences represent relatively fixed markers for seawater concentration and ensure that threshold concentration levels are reached.…”

Section: Resultsmentioning

confidence: 96%

“…Seawater evaporation yields predictable mineral facies characterized by a progression from carbonates to sulfates to chlorides (Holser, 1979). Gypsum and anhydrite dominate the removal of Ca during these stages of evaporation in modern seawater, and previous work indicates that lighter Ca isotopes are preferentially removed while minerals from more advanced stages of evaporation become enriched in heavier isotopes (Harouaka et al, 2014;Hensley, 2006). In modern SO 4 -rich seawater (SO 4 /Ca = 2.7), nearly all the original Ca is depleted by sulfate minerals before reaching halite.…”

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Calcium isotopes in evaporites record variations in Phanerozoic seawater SO4 and Ca

Blättler

Higgins

2014

Geology

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Reconstructing variations in the major element chemistry of seawater provides constraints on how the global carbon and sulfur cycles have changed over geological time, but archives for this information are rare. This work generates a new independent record of ancient seawater composition, in particular the relative abundance of Ca and SO 4 , through Ca isotope measurements in marine evaporites. Evaporite sequences that reach halite saturation record large Ca isotope variability if SO 4 > Ca, whereas a small range in Ca isotope ratios is observed if Ca > SO 4 . Analyses of geological evaporites indicate SO 4 -rich seawater in the Neogene and Permian and Ca-rich seawater in the Cretaceous and Silurian. These results agree with previous reconstructions using fluid inclusions in halite, and demonstrate a new approach for extending our understanding of oceanic and geochemical evolution. INTRODUCTIONThe major element chemistry of seawater is linked to the global carbon cycle and climate through weathering of silicate rocks, formation of clays, and burial of calcium carbonate, and to the oxidation of Earth's surface environment through cycling of seawater SO 4 . Changes in seawater chemistry over the Phanerozoic have been proposed to explain a range of observations, including the occurrence of inorganic marine carbonates as either aragonite or calcite (Sandberg, 1983), the presence of MgSO 4 or KCl in late-stage evaporite minerals (Hardie, 1996), and the chemistry of fluid inclusions within evaporitic halite (Brennan and Lowenstein, 2002;Horita et al., 2002;Lowenstein et al., 2001Lowenstein et al., , 2005. Many aspects of these records, however, remain untested. Several assumptions are required to transform fluid inclusion analyses into presumed seawater composition, due to the absence of certain ionic species, the evolved nature of the brine, and its extended storage in halite (Brennan et al., 2013). Other data sets, such as the composition of mid-ocean ridge flank veins (Coggon et al., 2010) and Mg/Ca ratios in well-preserved fossils (Dickson, 2002), generally confirm the direction of the fluid inclusion trends, but differences in the timing and magnitude of key changes suggest that the true seawater signatures contained in these records are yet to be resolved (Broecker, 2013).Ca isotope ratios in gypsum and anhydrite evaporites provide new independent evidence for intervals of Ca-rich seas and SO 4 -rich seas. Seawater evaporation yields predictable mineral facies characterized by a progression from carbonates to sulfates to chlorides (Holser, 1979). Gypsum and anhydrite dominate the removal of Ca during these stages of evaporation in modern seawater, and previous work indicates that lighter Ca isotopes are preferentially removed while minerals from more advanced stages of evaporation become enriched in heavier isotopes (Harouaka et al., 2014;Hensley, 2006). In modern SO 4 -rich seawater (SO 4 /Ca = 2.7), nearly all the original Ca is depleted by sulfate minerals before reaching halite. Fluid inclusions within halite...

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Section: Resultsmentioning

confidence: 96%

mentioning

confidence: 99%

Calcium isotopes in evaporites record variations in Phanerozoic seawater SO4 and Ca

Blättler

Higgins

2014

Geology

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“…Gypsum also preferentially incorporates light Ca compared to dissolved Ca (Harouaka et al 2014). Zhu and MacDougall (1998) have made the first attempt to investigate the global Ca cycle.…”

Section: Fractionations During Carbonate Precipitationmentioning

confidence: 99%

Isotope Fractionation Processes of Selected Elements

Hoefs

2015

Stable Isotope Geochemistry

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“…Geochemistry, Geophysics, Geosystems more enriched in 40 Ca relative to the lake water calcium. This calcium isotope fractionation factor for gypsum precipitation can be compared to Harouaka et al (2014), who reported calcium isotope fractionation between À0.8‰ and À2.25‰ in gypsum precipitated under a range of experimental conditions. The calcium isotope fractionation for gypsum reported by Harouaka et al (2014) has a slightly wider range than the calcium isotope fractionation during gypsum precipitation reported by Blättler and Higgins (2014; À1‰) and Hensley (2006;~À0.9‰).…”

Section: 1029/2018gc007898mentioning

confidence: 74%

“…There has been an attempt to attribute calcium isotope fractionation quantitatively to temperature (Marriott et al, ); however, it may be that the apparent temperature dependence of calcium isotope fractionation is due to changes in the relative size and growth rate of calcite, which vary with salinity, pH, and temperature (Tang et al, ; Zuddas & Mucci, ). Calcium isotope fractionation during gypsum precipitation is less well known, but a series of experiments have suggested that it is between −0.8‰ and −2.25‰ (Blättler & Higgins, ; Harouaka et al, ; Harouaka et al, ; Hensley, ). Harouaka et al () found that the calcium isotopic fractionation factor depends on the crystal face of gypsum growth.…”

Section: Introductionmentioning

confidence: 99%

The Calcium Isotope Systematics of the Late Quaternary Dead Sea Basin Lakes

Bradbury

Torfstein

Wong

et al. 2018

Geochem Geophys Geosyst

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We report the calcium isotopic composition (δ44Ca) of primary aragonite laminae, primary gypsum, and secondary gypsum in sediments deposited from Lake Lisan, the last glacial cycle of the Dead Sea (70–14.5 ka). The δ44Ca of primary gypsum varies between 0.17‰ and 0.71‰ versus bulk silicate earth, with an average of 0.29‰, whereas the aragonite δ44Ca varies between −0.68‰ and −0.16‰ with an average of −0.4‰. The secondary gypsum δ44Ca is close to the calcium isotope composition of the aragonite, averaging at −0.3‰. The aragonite δ44Ca shows small variations temporally in sync with lake level fluctuations, suggesting the aragonite δ44Ca reflects changes in the lake calcium balance, which in turn reflects changes in the local hydrological cycle. The secondary gypsum calcium isotope composition (−0.3‰) overlaps with that of coeval aragonite, suggesting the calcium for secondary gypsum was derived from the aragonite through quantitative, or near‐isotopic equilibrium, recrystallization of the aragonite to gypsum after the lake desiccation and exposure of sediments during the Holocene. A numerical box model is used to explore the effect of changing lake water levels on the calcium isotope composition of the aragonite and gypsum in the lake. The relatively low variability in the δ44Ca over the lake's history suggests that a high‐concentration calcium‐rich brine buffers the calcium cycle.

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Experimental investigation of Ca isotopic fractionation during abiotic gypsum precipitation

Cited by 42 publications

References 62 publications

Calcium isotopes in evaporites record variations in Phanerozoic seawater SO4 and Ca

Calcium isotopes in evaporites record variations in Phanerozoic seawater SO4 and Ca

Isotope Fractionation Processes of Selected Elements

The Calcium Isotope Systematics of the Late Quaternary Dead Sea Basin Lakes

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