The role of phosphate on non-skeletal carbonate production in a Cretaceous alkaline lake

Pietzsch, Raphael; Tosca, Nicholas J.; Gomes, J.P.; Roest‐Ellis, Sascha; Sartorato, Ana Carolina Leonel; Tonietto, Sandra Nélis

doi:10.1016/j.gca.2021.09.032

Cited by 8 publications

(7 citation statements)

References 103 publications

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“…Another example of mineral phases undetected by bulk analyses but evidenced by quantitative SEM-EDXS analyses are the P-and S-bearing phases. P-bearing phases usually consist of Papatite, which is widely found in nature and have lately been increasingly reported in carbonate deposits/microbialites from alkaline lakes (Zeyen et al, 2021;Pietzsch et al, 2022). Some F and Cl enrichment was detected in P-apatite, consistent with the presence of chlor-and fluoroapatite.…”

Section: Advantage Of the Quantitative Sem-edxs Approach: Identifying...mentioning

confidence: 88%

“…In Mari Ermi stromatolites, P-apatite phases may result from the diagenetic decomposition of P-containing organic matter and the diversion of part of the released orthophosphate anions to apatite precipitation favored by the high Ca concentration in seawater (Baturin, 1982(Baturin, , 1988. Alternatively, they may form authigenically with relatively high dissolved orthophosphate concentrations possibly favored by evaporation and high alkalinity as suggested by Pietzsch et al (2022).…”

Section: Advantage Of the Quantitative Sem-edxs Approach: Identifying...mentioning

confidence: 99%

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Mapping mineralogical heterogeneities at the nm-scale by scanning electron microscopy in modern Sardinian stromatolites: Deciphering the origin of their laminations

et al. 2022

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Section: Advantage Of the Quantitative Sem-edxs Approach: Identifying...mentioning

confidence: 88%

Section: Advantage Of the Quantitative Sem-edxs Approach: Identifying...mentioning

confidence: 99%

Mapping mineralogical heterogeneities at the nm-scale by scanning electron microscopy in modern Sardinian stromatolites: Deciphering the origin of their laminations

et al. 2022

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“…The limitation of dolomite formation within lake water columns or near the Earth's surface in highly alkaline lakes might also be attributed to phosphate inhibition of calcium carbonate precipitation and the rarity of finely particulate (micritic) calcite or aragonite precipitates (Pietzsch et al ., 2022). High alkalinity can enhance the accumulation rate of phosphate in lake waters, and phosphate is the most effective inhibitor to suppress the nucleation of new CaCO 3 and promote growth of calcite crystals on pre‐existing substrates in the Cretaceous alkaline lakes along the South Atlantic margin (Pietzsch et al ., 2022). The enhanced phosphate inhibition of calcium carbonate precipitation by high alkalinity can explain the rarity of microscopic calcite and aragonite (<70 μm) in the Fengcheng Formation, not only in the dolomite‐rich mudstones, but also in the dolomite‐deficient mudstones.…”

Section: Discussionmentioning

confidence: 99%

Constraints on dolomite formation in a Late Palaeozoic saline alkaline lake deposit, Junggar Basin, north‐west China

2023

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Alkaline lakes (pH > 9) are among the few modern sedimentary environments that are hydrochemically favourable for low‐temperature dolomite formation. While Mg‐clays and Mg‐evaporites also form more easily in alkaline environments, few studies have focused on how the kinetically inhibited dolomite wins the competition for Mg2+. Here, a basin‐wide survey of the distribution, paragenesis and stable C, O and Mg isotopes of main Mg‐rich minerals in the Late Palaeozoic saline alkaline lake deposit of the north‐west Junggar Basin, north‐west China, is conducted to study the influence of the formation and diagenesis of eitelite, northupite and Mg‐clays on dolomite formation. Large, isolated dolomite crystals (20 to 70 μm in diameter), show positive δ13C values (ranging from +1 to +7‰) and a restricted distribution in the mudstones of the lake‐transitional zone. These crystals have been interpreted as organogenic dolomite driven by methanogenesis via fermentation of organic substrates. The δ18O values of dolomitic mudstones (from −7.4 to +3.4‰), calcitic mudstones (from −15.1 to −3.3‰) and bedded Na‐carbonate evaporites (from +0.08 to +3.7‰), together with their Mg isotopic compositions, suggest that dolomite was not enriched in the most concentrated environments or during stages with most Mg sources, but in the organic‐rich deposits containing few other authigenic Mg‐rich minerals. Dolomite is at a competitive disadvantage for Mg2+ ions compared to Mg‐evaporite and Mg‐clay minerals due to its slow crystallization rates and the deficiency of micritic calcium carbonate precursors. However, it can nucleate and progressively grow into large crystals (>20 μm) if bacterial methanogenesis could effectively lower porewater pH (<8.5) and induce the dissolution of generated eitelite, northupite or Mg‐clays. These findings suggest that high salinity and/or high alkalinity are not always favourable conditions for dolomite formation and highlight the active role of pH fluctuations in inducing low‐temperature dolomite formation.

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“…Instead, SI values are higher. Recently, Pietzsch et al (2022), suggested that in some alkaline lakes, orthophosphate concentrations are high and inhibit crystalline anhydrous CaCO 3 precipitation, allowing the onset of saturation levels as high as the solubility of ACC. Unfortunately, this cannot be further tested here since dissolved PO 4 2− concentrations are only reported in eleven microbialite-forming environments of our database.…”

Section: Discussionmentioning

confidence: 99%

The chemical conditions necessary for the formation of microbialites

Caumartin¹,

Benzerara²,

Havas³

et al. 2023

Geochem. Persp. Let.

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Whether biological and/or physico-chemical variations may have changed the abundance of microbialites over geological times remains debated. This calls for a better appraisal of the conditions necessary for the formation of modern microbialites. Here, we compiled datasets from 140 aqueous environments where modern microbialites have been reported, including their respective physico-chemical parameters. By analysing this database, we find that solutions where microbialites form have a relatively high saturation with calcite, the chemical activities of Ca 2þ and CO 3 2− being controlled by the solubility of amorphous calcium carbonate (ACC) or monohydrocalcite (MHC) in most of these localities. Further statistical analyses of two databases listing ∼8000 continental aqueous systems show that only a few of them display saturation with ACC/MHC, appearing as candidates for the detection of overlooked microbialites.

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The role of phosphate on non-skeletal carbonate production in a Cretaceous alkaline lake

Cited by 8 publications

References 103 publications

Mapping mineralogical heterogeneities at the nm-scale by scanning electron microscopy in modern Sardinian stromatolites: Deciphering the origin of their laminations

Mapping mineralogical heterogeneities at the nm-scale by scanning electron microscopy in modern Sardinian stromatolites: Deciphering the origin of their laminations

Constraints on dolomite formation in a Late Palaeozoic saline alkaline lake deposit, Junggar Basin, north‐west China

The chemical conditions necessary for the formation of microbialites

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