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It has been known for some time that viable palaeoclimatic information should be recorded in groundwater-fed riverine tufas, particularly barrage, paludal or spring-line deposits. Stable isotope variation in active tufa-depositing systems is well understood. Variability in δ¹⁸O is driven mainly by changes in water temperature and the δ¹⁸O value of the recharging water. Variability in δ¹³C reflects principally the relative contribution of isotopically light CO₂ from soil organic matter, and isotopically heavier carbon derived from the dissolution of the aquifer limestone, modulated by equilibration of the aquifer, spring and stream water with atmospheric CO₂ (degassing) and by in-aquifer or in-stream calcite precipitation. In fast-flowing riverine systems the effects of evaporation and in-stream biological activity are negligible. Disequilibrium isotope effects away from actively degassing springs are probably very small, although …