Late Pleistocene Climate and Dust Source From the Mobarakabad Loess-Paleosol Sequence, Northern Foothills of the Alborz Mountains, Northern Iran

Paleoclimatic investigation of loess-paleosol sequences from northern Iran is important for understanding past changes in a region highly sensitive to shifts in precipitation, and along potential routes of past human migration. Here, we present carbon and oxygen isotopic compositions of bulk carbonate (delta C-13(bc) and delta O-18(bc), respectively) coupled with particle size distributions of samples from the Mobarakabad section, northern Iran, to study past wind dynamics and hydroclimate. We also present new initial clay-sized Hf-Nd isotope results from key horizons in order to assess general dust sources. Variations of delta C-13(bc) and delta O-18(bc) values of modern soils compared to paleosols allow reconstruction of late Pleistocene-Holocene climate change in the area. Our results show severe drought during a major eolian deposition phase (EDP) after 34 ka. The thickness and PSD of the C horizon of unit 5 suggest significant shifts in loess sources and depositional environments during this EDP after 34 ka. Indeed, based on our new clay-sized Hf-Nd data, we hypothesize that the loess unit 5 might originate from the young crustal source of the Alborz and Kopet Dagh mountains. In general, the PSD of C horizons in the section is bimodal in the silt fraction and the very small, very fine clay fraction, with a mode at c. 1 mu m in the modern soil and paleosols possibly produced by weathering and pedogenic processes. There also appears to be a good correlation between delta C-13(bc) and delta O-18(bc) values, differentiating phases of loess accumulation and paleosol formation and hence providing quantitative data for reconstructing paleoclimatic conditions in the study area.