摘要
从黄土高原中部洛川和环县两个剖面选取若干黄土和古土壤样品,分为三种粒级(>45μm、2～45μm、<2μm),挑出>45μm粒级中的根状结核与蜗牛壳化石碎片,分别测定δ13C和δ18O值。结果显示,两个剖面不同粒级组分的δ13C和δ18O值表现出相似的分布规律。洛川剖面的根状结核和蜗牛壳与分粒级样品中的<2μm粒级中碳酸盐的δ13C和δ18O值最为接近,处于相同的区域内;而>45μm粒级中的δ13C和δ18O值与其他样品有明显的差别。因此,可以认为黄土-古土壤中<2μm粒级中所含的碳酸盐可代表成壤碳酸盐,其蕴涵的地球化学信息可用以重建成壤时的古气候和古环境条件。
Carbonate is a common component in Chinese loess, and both detrital and authigenic carbonates occur in loess sequences. Authigenic carbonate includes important climatic and ecological information associated with soil forming and/or post depositional processes. In this study, samples of the loess and paleosol are collected from the Luochuan and Huanxian loess sections, the Loess Plateau, China. First, these samples are separated into three different grain size fractions, i.e. > 45 μm, 2～45 μm, and < 2 μm. Second, mollusk shell fragments and rhizocretion are picked up from the > 45 μm fraction under the microscope. Then oxygen and carbon isotopic compositions of these samples are measured using MAT 252, respectively. The results show that the finest fraction, i.e. < 2 μm, has the same fluctuation range of the δ13C and δ18O values with the mollusk shell and rhizocretion at the same depth for both sections. The δ13C and δ18O values in the > 45 μm fraction are very different from any other fractions. It is well known that the mollusk shell and rhizocretion were formed as the loess and paleosol came into being and they are typical authigenic carbonates in the multiminerals system of the loess and paleosol. Therefore, it can be concluded that carbonates in the < 2 μm fraction from the loess and paleosol samples can be regarded as authigenic carbonate. It is a good indicator of the summer monsoon induced weathering and pedogenesis fluctuations and can be used to reconstruct the conditions of the paleoclimate and paleoenvironment.
出处
《地球化学》
CAS
CSCD
北大核心
2002年第2期105-112,共8页
Geochimica
基金
国家重点基础研究发展规划项目(G1999043400)
国家杰出青年基金(49725307)
关键词
黄土
原生碳酸盐
次生碳酸盐
分粒级
氧同位素
碳同位素
古环境
古土壤
loess
detrital carbonate
authigenic carbonate
grain size fractions
carbon and oxygen isotopic composition
