The origin theory of the spherical rock mass of calcium carbonate (spherical concretion) that is universally formed in sedimentary rocks has been debated for about a century.However, its clear formation remains unclear, and verification as a unified theory has been an issue for the relational expressions that express the formation conditions and formation speed.

　This time, the research group verified the formation rate and formation conditions from more than 100 spherical concretions in Japan and overseas.As a result, it was clarified that spherical concretions are formed by a rapid reaction between carbon of biological origin and calcium ions in seawater.In addition, it was discovered for the first time in the world that the formation conditions are uniformly and universally expressed by the relational expression D = VL (D: diffusion coefficient, V: formation rate, L: reaction edge width).

　Furthermore, regarding the formation rate of carbonate spherical concretion, it overturns the conventional concept that it takes hundreds of thousands to millions of years, and actually grows at a very high rate of several months to several years. I also revealed that.

　From the formation conditions clarified this time, it is possible to perform a reproduction experiment of spherical concretion formation.This will give momentum to the application and practical application of maintenance-free long-term groundwater control (sealing) technology associated with the repair of cracks in concrete in tunnels and the use of large-scale underground environments (linear, energy underground storage, underground waste disposal, etc.). Is expected to be attached.

Paper information:[Scientific Reports] Generalized conditions of spherical carbonate concretion formation around decaying organic matter in early diagenesis