Investigation of disequilibrium clumped isotope fractionation in (speleothem) CaCO3 with cave analogous laboratory experiments using thin films of flowing solution

Abstract. Calcium carbonate (CaCO3) plays an important role in the natural environment as a major constituent of the skeleton and supporting structure of marine life and has high economic importance as additive in food, chemicals and medical products. Pure CaCO3 occurs in the three different polymorphs calcite, aragonite and vaterite, whereof calcite is the most abundant and best characterized mineral. In contrast, little is known about the rare polymorph vaterite, in particular with regard to the oxygen isotope fractionation between H2O and the mineral. Synthetic precipitation of vaterite in the laboratory typically involves rapid processes and isotopic non-equilibrium, which excludes isotope studies focused on characterization of vaterite at equilibrium conditions. Here, we used a new experimental approach that enables vaterite mineral formation from an isotopically equilibrated solution. The solution consists of a ~ 0.007 mol L-1 CaCO3 solution that is saturated with NaCl at room temperature (up to 6.5 mol L-1). Vaterite precipitated as single phase or major phase (≥ 94%) in experiments performed between 23 and 91 °C. Only at 80 °C was vaterite a minor phase with a relative abundance of 27%. The high mineral yield of up to 235 mg relative to a total dissolved CaCO3 amount of 370 mg enables an investigation of the oxygen isotope fractionation between mineral and water, and the determination of clumped isotope values in vaterite.

Download Full-text

Functionally graded SrTiO3–BaTiO3 thin films prepared by the hydrothermal-electrochemical method under flowing solution

Journal of Materials Research ◽

10.1557/jmr.1998.0117 ◽

1998 ◽

Vol 13 (4) ◽

pp. 875-879 ◽

Cited By ~ 21

Author(s):

Masahiro Yoshimura ◽

Wojciech Suchanek ◽

Tomoaki Watanabe ◽

Bungo Sakurai ◽

Masanori Abe

Keyword(s):

Thin Films ◽

Electrochemical Method ◽

Single Phase ◽

Flow System ◽

Functionally Graded ◽

Processing Conditions ◽

Synthesis Parameters ◽

Variable Chemical ◽

Hydrothermal Electrochemical Method ◽

Flowing Solution

BaTiO3, SrTiO3, and BaxSr1−x TiO3 thin films, as well as multilayers in the SrTiO3-BaTiO3 system, have been prepared on Ti substrates in newly constructed flow-system equipment by the hydrothermal-electrochemical method. The synthesis parameters (temperature of 120–200 °C, flow rate of 1–50 cm3/min) allow fabrication of dense, single-phase films with different morphology by controlling nucleation and/or growth rates. The flow system enables also an easy fabrication of SrTiO3/BaTiO3 and BaTiO3/SrTiO3 multilayers with variable chemical composition and microstructure across the film thickness. The multilayers can be prepared in only one experiment by simply changing the kind of flowing solution and/or adjusting the processing conditions.

Download Full-text

Belemnites, clumped isotopes and oxygen fractionation

10.5194/egusphere-egu2020-260 ◽

2020 ◽

Author(s):

Madeleine Vickers ◽

Stefano Bernasconi ◽

Clemens Ullmann ◽

Stephen Hesselbo ◽

Gregory Price ◽

...

Keyword(s):

Oxygen Isotope ◽

Isotope Fractionation ◽

Clumped Isotopes ◽

Fractionation Factor ◽

Oxygen Isotope Fractionation ◽

Temperature Reconstructions ◽

Life Habits ◽

Stable Oxygen ◽

Clumped Isotope ◽

Low Precipitation

Belemnite calcite has been used extensively for Jurassic and Cretaceous stable oxygen isotope temperature reconstructions since the 1950s. However, with the advent of clumped isotope thermometry, a consistent offset between reconstructed &#948;18O temperatures vs &#916;47 temperatures from the same belemnites has been observed. We investigate the causes of this offset by analyzing samples from the aragonitic phragmacone and calcitic rostrum from the same Cylindroteuthis belemnites, along with other aragonitic benthos, from the Callovian-aged Christian Malford Lagerst&#228;tte, U.K. Our new clumped isotope data suggest that the water-calcite 18O-fractionation factor in belemnite calcite was larger than that of the commonly used &#948;18O thermometry equations (e.g. Kim and O&#8217;Neil, 1997), and which is currently observed in other marine calcifiers. Our reconstructions suggest that the oxygen isotope fractionation is compatible with that observed in slow-forming abiotic calcites (e.g. Coplen, 2007) and in rapidly precipitating Travertines (Kele et al. 2015). The application of more established &#948;18O thermometry equations (Kim and O&#8217;Neil, 1997) to belemnite calcite for temperature reconstructions has resulted in a consistent underestimation of belemnite calcification temperatures, which has led to erroneous conclusions about belemnite life habits, and underestimation of global temperatures during these greenhouse times. We therefore advocate the use of calcite equations based on low precipitation rate experiments (e.g. Coplen, 2007; Kele et al., 2015) for belemnite rostra temperature reconstructions.

Download Full-text