The behavior of strontium during the replacement of aragonite by calcite, in a closed system between 40°C and 98°C, has been experimentally investigated. The experiments were conducted in CaCl2 solutions, with and without NaCl. The distribution coefficient of strontium in calcite (λSr2+C) was found to be affected only slightly by temperature changes, and almost insignificantly by the presence of NaCl. λSr2+C values at 0.01 mCa2+ (its concentration in normal sea water) are: 0.055 at 40°C and 0.058 at 98°C. These results indicate that the low (around 500 ppm) concentration of strontium in ancient limestones could have been brought about by aragonite-to-calcite transformation in a system open to sea water, and are not necessarily indicative of replacement in fresh waters.