High-resolution decording of terrestrial paleo-climate recorder in laminated tufas

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A tufa, a freshwater carbonate deposited in a limestone area, is an excellent tool for quantitative and highresolution analysis of terrestrial paleo-climate. Results of our investigation reveal that 1) laminated texture of tufas can be treated as annual layering developed due to seasonal change in precipitation rate of calcite. Estimation of microbial biomass shows that 2) the precipitation is not induced by photosynthesis of cyanobacteria living on the tufa surface. This and results of chemical analyses conduct to the conclusion that 3) equilibrium in terms of oxygen stable isotope and minor metal elements is confirmed in the calcite precipitation.These contexts make paleo-climatic analyses using a laminated tufa possible, and the analyses were performed for the specimens collected from Shirokawa (Ehime Prefecture) and Niimi (Okayama Prefecture). We found that 4) oxygen isotopic composition changes very regularly together with annual layering. The change is reflected from regular seasonal change in water temperature. Furthermore, we realized that 5) rainfall events are recorded as brown-colored bands, which are rich in Si, and Al. Excellent correlation between positions of the bands and periods of the rainfall events was recognized.This study provided new aspects of depositional processes and conditions of laminated tufas, and confirmed importance of the tufas in terms of paleo-climatological analytical tools