Late Pleistocene dust dynamics and pedogenesis in Southern Eurasia - Detailed insights from the loess profile Toshan (NE Iran)

The last interglacial Luvisol/Phaeozem-like (∼MIS 5e) and the early glacial interstadial steppic palaeosols (∼MIS 5 c and a) are characterized by gradually increasing grain-size and decreasing degrees in decomposition of micaceous and mafic minerals. Pronounced feldspar weathering is detected in the last interglacial and modern soils only, which formed under reduced or absent dust deposition on penultimate and last glacial loess, respectively (postsedimentary). The overall pedosedimentary conditions correspond to large scale trends of increasing drought, dust accumulation and wind strength in southern Eurasia in relation to decreasing moisture availability towards the early Pleniglacial (∼MIS 4), causing soil formation under ongoing dust deposition (synsedimentary). Similar intervals of synsedimentary soil formation are recorded during the interglacial/interstadial-stadial transitions of the early glacial and during pleniglacial (∼MIS 4 to 2) interstadials. The latter are marked by gradual increases in magnetic susceptibility, colour and decreasing texture. Conversely, silicate weathering could not be detected, suggesting that grain-size fluctuations are a primary feature. Thus, windy and arid pleniglacial conditions in southern Eurasia were interrupted by intermittent phases of synsedimentary soil formation, in response to short-lived and relatively moist interstadials. Although the interrelation of these incipient soils, throughout southern Eurasia is afflicted with considerable restrictions, the oscillatory pattern of the Toshan LPS bears great similarity with millennial-scale oscillations recorded in limnic archives of western Asia.