长江三角洲古土壤发育与晚更新世末海平面变化的耦合关系

文章运用沉积学、元素地球化学和稳定碳同位素等方法,研究长江三角洲古土壤记录的古环境和古气候特征。古土壤与下伏漫滩沉积在粒度组成和化学风化程度等方面有继承性和延续性。不同剖面母质粒度组成受局部地形起伏控制,具有泛滥平原沉积特征。结合沉积学特征及古生物研究分析表明,古土壤成土母质应为洪泛平原沉积物。有机稳定碳同位素分析显示,古土壤形成过程中气候有逐渐变干的趋势。各剖面粒度向上变细可能反映母质沉积时泛滥平原淹没能力降低、河流水位不断下降。古土壤底部化学风化程度最低,反映早期以母质堆积为主间或有成土作用;向上化学风化程度增强,指示暴露成土作用加强,而沉积作用减弱;顶部风化程度又逐渐减弱,可能是降雨量持续减少以及气候的变干变冷造成的。古土壤母质堆积过程中河流水位下降及化学风化程度的变化,是晚更新世末海平面降低过程中古河谷下切、气候变干变冷的结果。

CORRELATION OF PALEOSOL DEVELOPMENT IN THE CHANGJIANG DELTA WITH SEA LEVEL FLUCTUATIONS IN THE LATE PLEISTOCENE

The paleo environment reconstruction was made based on sedimentological, geochemical features and δ 13 C values of the paleosol, developed on flood plain sediments, in Changjiang delta. δ 13 C values imply that climate changed from humid and warm in the early stage of the paleosol development to dry and cold in the late stage. Grain size distribution shows that the sedimentary dynamic weakened as the incised valley deepened. Variations of CIA and contents of active elements demonstrate chemical weathering is primarily controlled by sedimentary process in the early stage, and by the climate change later on. Combination of the depositional environments and paleoclimatic changes indicates that the paleosol was formed during the transition from the last interstadial to Last Glacial Maximum while the sea level was falling.