Loess-paleosol sedimentological characteristics in northern Iran since the last interglacial and their paleoenvironmental significance

Abstract

The climatic signals recorded by loess sequences vary between different regions, which makes it important to study loess sequences worldwide. The loess deposits in northern Iran are situated in the transitional zone between the European loess and Central Asian loess. However, the depositional dynamics and paleoenvironmental significance of the loess deposits in this region are not well understood, making it difficult to establish detailed correlations with loess deposits elsewhere, partly due to the lack of systematic and high-resolution chronological control. We used K-feldspar pIR₅₀IR₂₉₀ and MET-pIRIR₂₅₀ luminescence dating protocols to date fifty-two K-feldspar samples from the Toshan-19 section in the northern foothills of the Alborz Mountains, northern Iran. These chronological data, along with the climate proxies of magnetic susceptibility and redness, combined with a comparison with published loess records from various regions, indicate the following: (1) K-feldspar luminescence ages obtained using pIRIR and MET-pIRIR protocols are consistent, and their luminescence ages up to ∼200 ka are deemed dependable. The loess at Toshan was primarily deposited during 78–24 ka, corresponding to MIS 4–2, and the paleosols developed during 139–78, and 24–1.7 ka, corresponding respectively to MIS 5, and late MIS 2–MIS 1. (2) Drier conditions prevailed during the last glacial and wetter conditions dominated during the last interglacial. Moisture variations during the substages of MIS 5 in this region indicate cold-dry and warm-wet climatic characteristics. The reasons for increased moisture from late MIS 2 onwards in this region still require further investigation. (3) The loess-paleosol records indicate a consistent pattern of climate change over Eurasia on the scale of the last interglacial-glacial cycle. During the substages of MIS 5, warm-wet and cold-dry conditions in northern Iran were in-phase with those on the Chinese Loess Plateau, Europe, and southern Tajikistan; however, they were anti-phased or out-of-phase with those in Xinjiang.