Origin of the tufa at Jiuzhaigou scenic spot in Sichuan

Jiuzhaigou is well known for its unique and gorgeous scenery. As a key factor of the landscape, tufa there has high tourist value and scientific value. The hydrochemistry, stable hydrogen and oxygen isotope ( delta D and delta super(18)O) in some key water samples and stable carbon isotope ( delta super(13)C) in dissolved inorganic carbon (DIC) as well as modern tufa are examined to understand the origin of the tufa and especially the CO sub(2) needed for the formation of the tufa at Jiuzhaigou, Sichuan. It is found that, (1) water of Jiuzhaigou is supplied by atmospheric precipitation; (2) the concentrations of HCO super(3) sub(-) and Ca super(2+) in the water of Jiuzhaigou, originated from the dissolution of carbonate rock by soil CO sub(2), are low; (3) according to the source of CO sub(2), the tufa at Jiuzhaigou is meteor-gene or supergene; (4) the large fractionation of carbon isotope between modern tufa and DIC at pearl shoal suggests that photosynthesis of algae there played important role in the tufa deposition.