9:15 AM - 9:30 AM
[MIS11-14] Estimation of formation mechanism and morphological condition in calcite concretion
Keywords:Spherical calcite concretion
In this study, we focused on calcite concretion produced in an eolian layer. Calcite concretion of the eolian layer is produced in three forms, spherical, plate-like, fish egg (globular gathering state). It is aimed to clarify the forming mechanism and the forming conditions in indoor experiments. We will report the current experiment status. CaCO3 is precipitated by evaporation in Utah's sand. In order to increase the solubility of the CaCO3 aqueous solution, CO2 is blown into the solvent. Ca(HCO3)2 is made in the solvent. By evaporating it CaCO3 is precipitated in the layer of sand to generate a concretion. Then Ca(HCO3)2 is made in the solvent. It evaporates to precipitate CaCO3 in the layer of sand.Utah's sand has an average particle diameter of 150 μm (Kawakami 2015). The minimum size of calcite concretion and Fe-oxide concretion discovered on Earth is several mm in diameter  and experiments are conducted with the aim of creating the size. CaCO3 concentration and evaporation rate are changed as parameters. X-ray CT is used to analyze CaCO3 in the experimental layer. In order to investigate whether CaCO3 and sand can be distinguished from X-ray CT images, a experiment was conducted when CaCO3 precipitated in the sand layer. The simulated sample was prepared by mixing sand from Navajo sandstone and a few mg of CaCO3. As a result of the X-ray CT experiment, it was confirmed that a CaCO3 having a size of 0.50 mm can be discriminated at a resolution of 0.019mm/pixel. It was also found that CaCO3 and sand are close in density, so it can not be determined that CaCO3 is not sufficiently larger than the average particle diameter of sand 150μm.
In the future, we will analyze the samples prepared in the experiment and try experiments under various conditions by adding experimental parameters as well as CaCO3 concentration, evaporation rate and sand filling rate. Then we will clarify the formation mechanism and the morphological condition of calcite concretion in the eolian layer.
 Yoshida et al.(2018) Science Advances Vol.4, no.12;Sally Latham Potter.2009 Chracteization of navajo sandstone hydrous ferric oxide concretions