Pleistocene dynamics of dust accumulation and soil formation in the southern Caspian Lowlands - New insights from the loess-paleosol sequence at Neka-Abelou, northern Iran

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

“…By contrast, the strong correlation between average mode size of early-middle MIS 3 loess at Mobarakabad (unit 4), Toshan, Now Deh, and Neka-Abelou with the geographical latitude of the sections (Figure 6) in northern Iran is in agreement with the findings of Kehl et al (2021), who suggested dust transport by north to northeasterly winds supplying coarse-grained dust to the NILP and finer facies along the NFAM. Currently, north to northeasterly winds are most frequent during late autumn and winter as the influence of the Siberian high-pressure cell intensifies (Kehl et al, 2021). Hence, similar wind dynamics during early-middle MIS 3, almost certainly, would have been responsible for the entrainment of coarse silt from the north and the transport of this coarse sediment to NFAM.…”

“…In contrast to the relatively fine-grained loess at Mobarakabad, the average median particle size of the Aghband loess in NLIP is (Ghafarpour et al, 2016), clay variations (this study), and OSL ages (Ghafarpour et al, 2017) at Mobarakabad and associated luminescence ages (red circles) of Toshan and Neka-Abelou sections (see Vlaminck et al, 2016;Kehl et al, 2021).…”

“…These buried horizons in modern soil and paleosols have clearly been affected by pedogenic processes, and their high clay content (with an increase in pedogenic smectite content) is the result of weathering and clay illuviation (Ghafarpour et al, 2016). Therefore, we argue that in the modern soil and paleosols, the dominant mode at c. 8.5-9.5 µm, with a secondary one in very fine clay fraction (c. (Vlaminck et al, 2016;Kehl et al, 2021), supplemented by data from the Aghband section (Lauer et al, 2017a) in the NILP. Note that with increasing latitude, the mode size of loess from early to middle MIS 3 increases (r 2 0.98), but it appears that there is a weaker trend in the mode size of loess samples in the sections at the NFAM within MIS 5 (see text).…”

“…Furthermore, these comparisons allow wider patterns to be identified that are independent of local topographic or proximal source influences. Previous studies in northern Iran defined the median particle size as 9.12-11 μm for least weathered loess at Neka-Abelou and Toshan sections (Figure 5) on the NFAM (Vlaminck et al, 2016;Kehl, et al, 2021). In particular, the modes of the C horizons of units 1-3 (10.7-12 μm) at Mobarakabad are comparable with the modal values of the loess (∼11 μm) in unit 5 at Toshan (Figure 6) and also with the mode size of loess in unit 3 (∼10.5 μm) at Neka-Abelou (Figure 6), both forming during MIS 5 (Lauer et al, 2017b;Kehl et al, 2021) (Figure 7).…”

“…These deposits represent outstanding archives of past climate in a region highly sensitive to changes in hydroclimate and potentially important in past human migrations (Shoaee et al, 2021) but otherwise poorly represented by past climate records. The loess units in the area are separated by paleosols showing various development degrees, providing valuable sedimentary archives of loess accumulation, soil, and paleosol formation within the loess units (Kehl et al, 2005;Frechen et al, 2009;Kehl, 2010;Khormali and Kehl, 2011;Ghafarpour et al, 2016Ghafarpour et al, , 2021Vlaminck et al, 2016Vlaminck et al, , 2018Lauer et al, 2017a;Lauer et al, 2017b;Shahriari et al, 2017;Pourmasoumi et al, 2019;Sharifigarmdareh et al, 2020;Kehl et al, 2021). These previous studies of loess-paleosol sequences in northern Iran mainly focused on dating of the deposits, particle size distributions, and paleosol formation in response to paleoprecipitation and paleopedogenic process, with little emphasis on phases of eolian deposition, meaning that additional detailed analyses of the loess units in particular are essential.…”