江西信江盆地晚白垩世塘边组成壤碳酸盐岩碳、氧同位素特征

摘要

利用古土壤成壤碳酸盐岩稳定同位素组成估算古代大气CO2浓度,是当前古气候环境研究的重要手段.对采自江西信江盆地晚白垩世圭峰群塘边组的成壤碳酸盐岩碳、氧同位素测试表明,δ13C(PDB)值在-4.30‰～-2.10‰之间,平均值为-2.84‰.δ18O(PDB)值在-6.62‰～-1.14‰之间,平均值为-3.62‰.由Cerling经验公式估算出晚白垩世Campanian晚期约75 Ma的大气CO2浓度在782～1 420 ppmv之间,平均值为1 181 ppmv,是当今大气CO2浓度的2～4倍.因此,基于信江盆地塘边组成壤碳酸盐岩的大气CO2浓度估算结果,可能指示了晚白垩世Campanian晚期存在一个大气CO2浓度高峰值,反映了晚白垩世大气CO2浓度的波动性.%The isotope composition of pedogenic carbonates in paleosols is an effective approach to quantitative reconstruction of atmospheric CO2 partial pressure.Stable isotope analysis of pedogenic carbonates from the Late Cretaceous Tangbian Formation in the Xinjiang Basin of Jiangxi Province was conducted to understand the paleoclimatic conditions.The carbon isotope compositions range from-4.30‰ to-2.10‰ (PDB) with an average of-2.84‰,and the oxygen isotope compositions range from-6.62‰ to-1.14‰ (PDB) with an average of -3.62‰.The CO2 partial pressure was calculated to be from 782 to 1 420 ppmv based on Cerling's formula with an average of 1 181 ppmv during the Campanian Stage (～75 Ma),which is about 2～4 times higher than that of the present-day level.Therefore,a marked high value of CO2 partial pressure probably occurred during the late Campanian Stage,possibly reflecting the undulation of Pco2 during the Late Cretaceous time.