高校地质学报2025，Vol.31Issue(6)：698-710,13.DOI:10.16108/j.issn1006-7493.2024094
云南曲靖上志留统—泥盆系古土壤的元素、Li同位素地球化学特征及其古气候意义
Elemental,Lithium Isotopic Composition and Paleoclimatic Significance of Upper Silurian-Devonian Paleosols in Qujing,Yunnan Province
摘要
Abstract
To explore the influence of plant landfall in the early Paleozoic on climate and environmental change in southwest China,we conducted elemental and lithium isotopic analyses of late Silurian-Devonian paleosols from Qujing City,Yunnan Province.Clay separation experiments were performed to eliminate the interference of unweathered primary minerals on the Li isotopic composition.The results show that the Chemical Index of Alteration(CIA)ranges from 66.8 to 82.7 with mean the degree of chemical weathering is moderate to strong.Compared with the upper Silurian and middle Devonian,the CIA average values(77.9±1.9)of the lower Devonian paleosols are higher,indicating enhanced chemical weathering.The Li contents in the clay fraction(<2 μm)range from 24.1 to 383.3×10-6,evidently higher than in the bulk samples(7.5 to 74.5×10-6)and the upper continental crust average(35±11×10-6),suggesting Li enrichment in the clay minerals during the chemical weathering process.The lithium isotopic compositions of the clay fraction(δ7LiClay,-7.0 ‰ to+2.2 ‰)are lower than the UCC(～0 ‰),with the greatest isotopic fractionation occurring in the early Devonian(-7.0‰).This is primarily due to stronger chemical weathering during this period,which led to the formation of more clay minerals that preferentially adsorbed lighter 6Li,resulting in more negative δ7Li values.Meanwhile,many well-preserved plant fossils have been found in the Xujiachong Formation of the Lower Devonian.Combined with plant fossil records from the same period globally,this suggests a link between the enhanced silicate weathering may be related to the evolution of higher plants.This study provides Li isotope evidence for the hypothesis that the landing of vascular plants in the early Devonian triggered enhanced chemical weathering and reduced CO2 levels,helping to improve the understanding of the interactions between vegetation,weathering,and climate.关键词
古土壤/元素地球化学/Li同位素组成/化学风化Key words
paleosol/element geochemistry/lithium isotope/chemical weathering分类
海洋科学引用本文复制引用
徐成笑,杨浩,管祎亭,吴卫华..云南曲靖上志留统—泥盆系古土壤的元素、Li同位素地球化学特征及其古气候意义[J].高校地质学报,2025,31(6):698-710,13.基金项目
国家自然科学基金(41991324 （）
41773007)资助 （）
