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.

Automated summary

The study of carbon and oxygen isotopic compositions of samples from the Mobarakabad section in northern Iran provides insights into late Pleistocene-Holocene climate change in the region. Results suggest a severe drought after 34 ka, with significant shifts in loess sources and depositional environments during this time period. The correlation between delta C-13(bc) and delta O-18(bc) values differentiates phases of loess accumulation and paleosol formation, offering quantitative data for reconstructing paleoclimatic conditions.