Some phenomenological aspects of carbonate geochemistry. The control effect of transition metals

Abstract

ZusammenfassungDie Gegens~itzlichkeit der Geochemie der Karbonateorganische oder anorganische Produktion -fiihrte zu einer widerspriichlichen Definition des Karbonatsystems AbstractThe dualism in carbonate geochemistry -organic or inorganic production -leads to an erroneous definition of the carbonate system. A different formulation of the chemical mechanism is proposed where traces of transition metals together with organic matter in natural environments play a central role in carbonate production. This approach is verified in a series of experiments using natural and artificial sea water and as chelating agents citric, tartaric, malonic, and oxalic acids with five transition metals: Ni, Co, Fe, Mn and Zn. The final product of carbonate precipitation depends on the type of metal acting as a central atom. In the series Ni, Co, Fe, Mn, Zn the potential for calcium uptake increases from Ni to Zn, while magnesium uptake increases in the opposit direction from Zn to Ni. Dolomite can precipitate from Mg-rich natural waters by the catalytic effect of Fe(II)-chelates. If the waters containing Fe(II)-chelates are exhausted with respect to magnesium carbonate, they will attack dolomite to form calcite.

Inorganic synthesis of Fe–Ca–Mg carbonates at low temperature

“…Nevertheless, additional mechanistic details are required to account for the occurrence of the following naturally-occurring low temperature phases: (1) high Mg siderite formed microbially from aqueous solutions with low Mg concentrations (e.g., , (2) microbial dolomite (e.g., Sánchez-Román et al, 2008a,b), and (3) bedded and lacustrine magnesite deposits (e.g., Mö ller, 1989;Thompson and Ferris, 1990). Mirsal and Zankl (1985) proposed a mechanism by which a metal chelate facilitates the production of Mg-bearing carbonates at low temperature from solution. In their experiments, citric, tartaric, malonic and/or oxalic acids associated with specific transition metal ions (Me: Ni, Co, Fe(II), Mn, or Zn) are believed to form an octahedral transition metal ion chelate bound at various coordination positions by: (1) an organic-ligand (L), (2) a bicarbonate (HCO 3 ) or carbonate anion (CO 3 ), and (3) water molecules.…”

Early diagenetic dolomitization and dedolomitization of Late Jurassic and earliest Cretaceous platform carbonates: A case study from the Jura Mountains (NW Switzerland, E France)

“…Under these geochemical conditions, dolomite crystals precipitate under microbial mediation (van Lith et al, 2003b). Metal enrichments in the organic burrow lining may additionally facilitate dolomite precipitation (Mirsal and Zankl, 1985). Dolomite precipitation may spread into the surrounding micritic matrix and thus create few mm-thick dolomitic zones of floating dolomite rhombs (Fig.…”

Some phenomenological aspects of carbonate geochemistry. The control effect of transition metals — Discussion

“…In order to reach the desired salinity of 55 %0, an additional amount of 31.53 g NaC1 had to be added. Although not mentioned by MIRSAL & ZANKL (1985), another addition has to be made. The Mg/Ca ratio of this artificial sea water is not 5.28 : because 4.98 g magnesium chloride and 1.10g calcium chloride were used, and no other forms of magnesium or calcium salts are involved, the Mg/Ca ratio is actually 3.27.…”

“…In their recent paper MIRSAL & ZANKL (1985) claimed to have synthesized dolomite at room temperature in only 10 days time, and all that was needed were a few well-defined chemicals. In other words, it would be relatively simple to duplicate the tests described by MIRSAL & ZANKL (1985) and thus con-*) Author's address: Dr. J. C. DE~LMAN, P.O.Box 1460, Eindhoven, The Netherlands.…”

“…In other words, it would be relatively simple to duplicate the tests described by MIRSAL & ZANKL (1985) and thus con-*) Author's address: Dr. J. C. DE~LMAN, P.O.Box 1460, Eindhoven, The Netherlands.…”