Aluminum is one of the most important and abundant elements on Earth’s surface. The dynamics of this element has been widely studied in acidic soils and in the soils of the Mediterranean bioclimatic regions while there are very limited data about the dynamics and forms of Al in Aridisols. The aim of this study was to evaluate the dynamics of Al forms in a relict palaeosol and its environmental significance in an arid setting of central Iran. The studied soil is located on an upper terrace without impacts of groundwater and alluvial materials from adjacent landforms. We investigated different forms of aluminum (total (Alt), amorphous (Alo) and crystalline (Ald)) and also the mineralogical composition of the soil using a highresolution sampling strategy (10 cm interval). The soil has the highest content of total Al near the surface. The amount of crystalline aluminum is the highest in the middle part of the pedon and does not show any significant trend with depth while the amount of amorphous aluminum, the Allophane index (Alo+ 0.5Feo) and Alo/Ald ratio increased exponentially towards the soil surface. Mineralogical analyses revealed that the clast fraction of the soil lacks in smectite and K-feldspar minerals while smectite is abundant in fine earth fraction in the middle part of the pedon. The K-feldspar content increased exponentially towards the soil surface with a maximum content in dust-derived vesicular horizons. These findings suggest the formation of smectite in the soil environment by pedogenic processes and the addition of K-feldspar onto the soil surface by dust. Therefore, the soil experienced a profound environmental change from an environment that was characterized by chemical weathering to an environment of the accumulation of Al-bearing dust. Our study highlights the importance of the dynamics of aluminum in arid soils which must be considered for paleoenvironmental reconstructions as well as considering Al as a product of hydrolysis processes and an immobile element of weathering in soils.

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