Geochemical Proxies For Stalagmite SI3 From Shizi Cave, NE Sichuan, Central China And Their Paleoclimatic Implications

TIMS U-Th dating was conducted on a stalagmite SI3 collected from Shizi cave, Nuoshuihe, northeastern Sichuan, Central China and it was found that SI3 developed from 54 to 46 ka before present. Based on a multi-analysis of geochemical proxies for this stalagmite, includingδ¹⁸O,δ¹³C, Mg/Ca, Ba/Ca, Sr/Ca and ⁸⁷Sr/⁸⁶Sr, palaeoclimate and palaeoenvironment for the period from 54 to 46 ka is explored. Theδ¹⁸O record for SI3 displays a high similarity with those for stalagmites MSL, MSD and D4 obtained from Hulu Cave, east China and Dongge Cave, southwest China, respectively. This suggests that theδ¹⁸O record for SI3 is closely related with summer monsoon variation in East Asia. However, some evidences seem to suggest that carbonates in SI3 are more ¹⁸O enriched compared with those deposited under oxygen isotopic equilibrium. There was probably kinetic fractionation when SI3 was developed. This is consistent with the fact that SI3 was collected near the entrance of Shizi Cave. The possible mechanism between theδ¹⁸O record of SI3 and the variation in East Asian summer monsoon was speculated. We suggest that in the East Asian summer monsoon domain, theδ¹⁸O record of some speleothem deposited even under non-equilibrium condition is still useful for summer monsoon investigation. Theδ¹³C and elemental proxies Mg/Ca, Ba/Ca, Sr/Ca for SI3 display a good positive correlation, indicating that they are significantly influenced by prior calcite precipitation that may occur in the epikarst or on the cave ceiling before the dripwater reach stalagmite SI3. Usually cold-dry climate would lead to more prior calcite precipitation and eventually result in higherδ¹³C, Mg/Ca, Ba/Ca, Sr/Ca in SI3. The ⁸⁷Sr/⁸⁶Sr ratio correlates negatively with Sr/Ca and varies generally in an positive direction withδ¹⁸O. The ⁸⁷Sr/⁸⁶Sr ratio for SI3 usually shows relatively higher values under relatively cold and dry climate, suggesting a relationship with dust activity in this area that has significantly higher ⁸⁷Sr/⁸⁶Sr ratios compared with limestone and would be more intensive under cold-dry climatic phase.