Depositional environment of biologically induced carbonate, tufa, developed in surface stream in Hirao-dai Plateau, Kitakyushu, Southwestern Japn

Abstract

Downstream of Ishizaka Spring in Hirao-dai Plateau, Kitakyushu, pH and Ca²⁺ concentration in surface stream water showed daily changes to the extent that the temperature effect of CO₂ outgassing on the carbonate deposition could be ignored. They were significant changed by sunshine duration. In May, it was found that about 80 % of the total precipitation was induced by biological activities such as photosynthesis. The tufa deposition rate accelerated biologically reached a maximum during spring and early summer with much discharge and/or sunshine: this is the reason for the annual layers found in the tufa deposition.