[M-IS14] Aqua planetology

[MIS14-P13] Formation mechanism of spherical concretions in Tatsukushi area: Possible analogy with spherical nodule in Gale crater, Mars

*Saki Asai¹, Hitoshi Hasegawa¹, Hidekazu Yoshida², Minoru Ikehara¹, Nagayoshi Katsuta³, Masakazu Nara¹, Yui Tomonao¹, Satoru Imai⁴ (1.Kochi University, 2.Nagoya University, 3.Gifu University, 4.Tosashimizu GeoPark)

Keywords:spherical concretion, organic matter origin, carbon isotope, Mars, Gale crater

On Earth, spherical carbonate (CaCO₃) concretions are widely recognized. Many of these concretions are centered on fossils, and thought to be formed by decaying of soft body organic matter as carbon source. On the other hand, carbonate concretions are also formed by inorganic precipitation of calcite-saturated groundwater in arid environment. In addition, Fe-oxide encrusted concretions are found both on Earth (Utah and Mongolia) and Mars (Meridiani Planum). Yoshida et al. (2018) proposed that Martian Fe-oxide concretions are formed by dissolution of pre-existing carbonate concretions. They further suggested that spherical-shaped nodules in Gale crater can also formed by similar process, although shape and size of the Gale nodules are more variable. Here we report that spherical and variable-shaped concretions in Tatsukushi area, western Kochi, whose shapes are resembling to Gale nodules. In order to understand formation mechanisms of concretions in Tatsukushi area, we performed analyses of X-ray CT scan, elemental mapping, and stable carbon and oxygen isotope on samples of variable shapes of concretion. The results reveal that large-sized spherical-shaped concretion can be formed by organic matter origin. In this presentation, we will discuss the similarity of both concretions in Tatuskushi area and Gale crater.


Reference

Yoshida, H., Hasegawa, H., et al. (2018). Fe-oxide concretions formed by interacting carbonate and acidic waters on Earth and Mars. Science advances, 4(12), eaau0872.