Variation of Oxygen and Carbon Isotope Compositions in Transformation of Speleothem Primary Aragonite to Secondary Calcite

Knowledge on the variations of oxygen and carbon isotope compositions in the transformation of speleothem primary aragonite to secondary calcite is the foundation of paleo-environmental studies using speleothem.A stalagmite SN15,which was collected from the Shennong Cave,Jiangxi Province,southeastern China,has been identified by XRD analyzing that its aragonite has partially inverted into calcite.The comparisons of carbon and oxygen isotopic data series between secondary calcite and corresponding primary aragonite within stalagmite SN15indicate that theδ13 C datum of calcite have a quite similar range to those of the aragonite,whereas theδ18 O values of calcite are depleted about 0.2‰-1.4‰at random.Our result suggests that the oxygen isotopic data of calcite can hardly be used to investigate the paleo-climatic changes with high-resolution.Carbon isotope composition of calcite seems to be inherited from the aragonite,but it should be cautious to use the carbon isotopic data in paleo-environmental studies because the mechanism of aragonite-to-calcite transformation has not been fully understood.