Magnetic properties and geochemistry of loess–paleosol sequences at the Nowdeh section in northeastern Iran

Abstract. The loess–paleosol sequences in the northeastern part of Iran serve as a high-resolution natural archive documenting climate and environmental changes. These sequences offer evidence of the interaction between the accumulation and erosion of aeolian and fluvial sediments during the Middle and Late Pleistocene periods. In this study, the Azadshahr (Nowdeh loess section) site was chosen to reconstruct Late Quaternary climate shifts. The 24 m thick Nowdeh loess–paleosol sequence was sampled for magnetic and geochemical analysis. The sampling involved 237 samples taken systematically at high resolution (10 cm intervals, selected samples, corresponding to peaks in magnetic susceptibility, underwent geochemical analysis to aid in the interpretation of paleoclimatic changes indicated by the magnetic signals). The magnetic susceptibility results of the loess–paleosol deposits revealed low values during cold and dry climate periods (loess) and high values during warm and humid climate periods (paleosol). The magnetic susceptibility at a depth of 22.1 m (approximately 130 ka) has significantly decreased, suggesting cold climate conditions at this time. The most substantial changes in magnetic susceptibility occur at depths between 18.6 and 21.3 m (approximately 100–120 ka). During this period, there are four phases of decrease (indicating cold and dry conditions) interspersed with three phases of increase (signifying warm and humid conditions) in magnetic susceptibility. The comparison of magnetic and geochemical data showed that variations in geochemical weathering ratios corresponded to changes in magnetic parameters. A high level of correlation was observed between the magnetic susceptibility intensity and ratios such as Rb / Sr, Mn / Ti, Zr / Ti, and Mn / Sr. The findings from this research indicate that the sedimentary section of Nowdeh has experienced six distinct climate periods over the last 160 kyr. Notably, three cold and dry periods occurred between three warm and humid periods. Additionally, during these climate phases, short-term cold (stadial) and warm (interstadial) intervals were also observed.