Extracting Mg isotope signatures of ancient seawater from marine halite: A reconnaissance

Xia, Zhiguang; Horita, Juske; Reuning, Lars; Bialik, Or M.; Hu, Zhongya; Waldmann, Nicolás; Liu, Chuan; Li, Weiqiang

doi:10.1016/j.chemgeo.2020.119768

Cited by 17 publications

(15 citation statements)

References 120 publications

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“…Yet, in order to obtain first order estimates of D mineral-brine , the d 26 Mg values of the natural salts were subtracted from the Mg isotopic composition of modern seawater (d 26 Mg = À0.83‰). It should be noted however, that d 26 Mg of seawater varied somewhat during the Cenozoic Era (Higgins and Schrag, 2015;Gothmann et al, 2017) and, possibly, throughout the Phanerozoic Eon (Li et al, 2015;Xia et al, 2020). Furthermore, reactions (e.g., dolomitization) and/or mixing with different Mg sources within the evaporitic basin may have changed the composition of the evaporating seawater and Galy, 2004;Foster et al, 2010;Ling et al, 2011) and of the evaporated Dead-Sea (DS) brine, from which the sample DScarnallite was precipitated, are presented for comparison.…”

Section: Magnesium Isotope Fractionation During Precipitation Of Mg-evaporitesmentioning

confidence: 99%

“…Also, further research is required to evaluate the potential effect of post-depositional alterations, such as recrystallization, on the Mg isotopic composition of these evaporites and, for natural sequences, local mineralogical, petrographic, and sedimentological study should supplement the Mg isotopes measurements to enable reconstruction of the conditions under which these evaporites formed. In addition, it is suggested that the high Mg concentration in these evaporites, together with the large isotope fractionations, may overprint the d 26 Mg signal derived from other low-Mg archives, such as Ca-carbonates or fluid inclusions in halite, if these Mg-evaporites are present in the same system, for example, as mineral inclusions (e.g., Xia et al, 2020).…”

Section: Evolution Of D 26 Mg Brine During Brine Evaporation and Mg-salts Precipitationmentioning

confidence: 99%

“…Thus, understanding and quantifying the Mg budget of the modern and ancient oceans are important to our understanding of how fundamental Earth processes, such as weathering, volcanism and sedimentation, have changed globally throughout the geological past, and how these processes are linked to Earth's carbon cycle and long-term climate change (e.g., Holland, 2005;Elderfield, 2010). The isotopic composition of dissolved Mg in seawater, d 26 Mg seawater , has recently been shown to be a reliable proxy for the reconstructions of the Mg budget of the modern and past oceans (e.g., Tipper et al, 2006;Pogge Von Strandmann et al, 2014;Higgins and Schrag, 2015;Li et al, 2015;Gothmann et al, 2017;Shalev et al, 2019;Xia et al, 2020). However, a full understanding of the isotopic compositions of the oceanic Mg inputs and outputs and reliable record of d 26 Mg seawater in the past are needed in order to reconstruct the oceanic Mg-isotope budget.…”

Section: Introductionmentioning

confidence: 99%

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The Mg isotope signature of marine Mg-evaporites

Shalev

Lazar

Halicz

et al. 2021

Geochimica et Cosmochimica Acta

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Marine Mg-evaporites are a small oceanic sink of magnesium, precipitating only from extremely evaporated brines. The isotopic composition of Mg in seawater, d 26 Mg seawater , has recently been shown to be an effective tool for reconstructing the Mg budget of the modern and past oceans. However, estimations of the Mg isotope fractionation between the Mg-evaporites and their precipitating solution are required for full quantification of the isotope effect of the evaporitic sink on d 26 Mg seawater , as well as for utilizing ancient evaporitic sequences as an archive for past d 26 Mg seawater . Here, we estimate the Mg isotope fractionation between Mg-evaporites and modern marine-derived brine along the course of seawater evaporation, up to degree evaporation of >200. The sequence of Mg-salts included epsomite (The following isotope fractionation values, either negative or positive, were calculated from the isotope difference between the salt and its precipitating brine, and from the evolution of d 26 Mg in the brine throughout the evaporation: D carnallite-brine = +1.1‰, D epsomite-brine = +0.59‰, D bischofite-brine = +0.33‰, D kieserite-brine = À0.2‰ and D kainitebrine = À1.3‰. Magnesium isotopic compositions determined on minerals from different ages in the geological record corroborate well these results. Due to precipitation of multi-mineral assemblages having isotope fractionation values of opposing signs, the d 26 Mg value of the brine changes only slightly (<0.5‰) throughout the evaporation path, despite the considerable Mg removal (>50%). The isotope fractionations are shown to correlate with the number of water molecules coordinated to the Mg 2+ and with Mg-O bond length in the mineral lattice.Given these isotope fractionations, it is calculated that a volume of 0.4 Á 10 6 -0.8 Á 10 6 Km 3 of a mono-mineral assemblage of kainite or carnallite needs to precipitate in order to change seawater d 26 Mg by only 0.1‰. This huge volume is by far larger than the volume of these minerals known to date in the global geological record. Therefore, it is concluded that the impact of Mg-evaporites formation on d 26 Mg seawater has been insignificant since the Proterozoic. The results of this study suggest that the Mg isotopic composition of Mg-evaporites preserved in the geological record of evaporitic basins may be used to: 1) quantify geochemical processes that fractionate Mg-isotopes within these basins, such as dolomitization; and 2) complete the secular variations curve of the marine d 26 Mg record using basins with well-established evaporitic sequences.

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Section: Magnesium Isotope Fractionation During Precipitation Of Mg-evaporitesmentioning

confidence: 99%

Section: Evolution Of D 26 Mg Brine During Brine Evaporation and Mg-salts Precipitationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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The Mg isotope signature of marine Mg-evaporites

Shalev

Lazar

Halicz

et al. 2021

Geochimica et Cosmochimica Acta

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“…An alternative seawater Mg isotope archive is marine halite. Bedded halite from marine evaporites contains primary uid inclusions, which preserve the Mg isotope composition of the contemporary seawater 20 . The advantage of the halite record is that seawater δ 26 Mg values can be directly measured from uid inclusions without the application of Mg isotope fractionation factors, which are needed for the Mg-carbonates.…”

mentioning

confidence: 99%

“…The advantage of the halite record is that seawater δ 26 Mg values can be directly measured from uid inclusions without the application of Mg isotope fractionation factors, which are needed for the Mg-carbonates. That is because precipitation of halite from evaporating seawater occurs prior to precipitation of Mg-bearing evaporite minerals 20 . Thus, the Mg in the brine and uid inclusions has the same Mg isotopic composition as contemporaneous seawater.…”

mentioning

confidence: 99%

The evolution of Earth’s surficial Mg cycle over the past 2 billion years

Xia

et al. 2022

Preprint

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The surficial cycling of Mg is directly coupled with the global carbon cycle, a predominant control of Earth’s climate. However, how Earth’s surficial Mg cycle evolved with time had been elusive. Magnesium isotope signatures of seawater (δ26Mgsw) track the surficial Mg cycle, which could provide crucial information on the carbon cycle in Earth’s history. Here, we present a reconstruction of δ26Mgsw evolution over the last 2 billion years using marine halite fluid inclusions and sedimentary dolostones. The two independent archives yield consistent evolutionary trends of δ26Mgsw for the past 430 million years, and the dolostone records extend the δ26Mgsw curve to 2 billion years ago. Modeling results of the net CO2 sequestration efficiency (EMg−CO2) by the surficial Mg cycle based on the δ26Mgsw record reveal a secular decline EMg−CO2 during the past 2 billion years, with the periods of low EMg−CO2 coinciding with ice ages in the Phanerozoic. Our work underlines a previously under-appreciated, but indispensable role of dolostones in regulating Earth’s climate on geologic time scales.

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Smithian–Spathian carbonate geochemistry in the northern Thaynes Group influenced by multiple styles of diagenesis

Todes,

Blattmann,

Vennemann

et al. 2024

The Depositional Record

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The Smithian–Spathian boundary interval is characterised by a positive carbon isotopic excursion in both δ13Ccarb and δ13Corg, concurrent with a major marine ecosystem reorganisation and the resurgence of microbialite facies. While these δ13C records have been traditionally interpreted as capturing global carbon cycle behaviour, recent studies have suggested that at least some excursions in early Triassic δ13C values may incorporate influences from authigenic or early diagenetic processes. To examine the mechanistic drivers of Smithian–Spathian boundary geochemistry, the carbonate geochemistry of a core from Georgetown, Idaho (USA), was analysed using a coupled δ44/40Ca, δ26Mg and trace‐metal framework. While the δ13C record in the Georgetown core is broadly similar to other Smithian–Spathian boundary sections, portions of the record coincide with substantial shifts in δ44/40Ca, δ26Mg and trace‐metal compositions that cannot feasibly be interpreted as primary. Furthermore, these geochemical variations correspond with lithology: The δ13C record is modulated by variations in the extent of dolomitisation, and the diagenetic styles recognised here coincide with individual lithostratigraphic units. A primary shift in local sea water δ13C values is inferred from the most geochemically unaltered strata, from ca 3‰ in the middle Smithian to ca 5‰ in the early Spathian, although the timing and pathway through which this occurs cannot be readily identified nor extrapolated globally. Therefore, the Georgetown core may not directly record exogenic carbon cycle evolution, showing that there is a need for the careful reconsideration of the Smithian–Spathian boundary—and more broadly, Early Triassic—geochemical records to examine potential local and diagenetic influences on sedimentary geochemistry.

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Extracting Mg isotope signatures of ancient seawater from marine halite: A reconnaissance

Cited by 17 publications

References 120 publications

The Mg isotope signature of marine Mg-evaporites

The Mg isotope signature of marine Mg-evaporites

The evolution of Earth’s surficial Mg cycle over the past 2 billion years

Smithian–Spathian carbonate geochemistry in the northern Thaynes Group influenced by multiple styles of diagenesis

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