Age, sedimentation, and soil formation in the Val Sorda loess sequence, Northern Italy.

The Val Sorda sequence is a key section for Quaternary stratigraphy of Northern Italy, because it is very well preserved and is the only loess section in the area providing 14C and luminescence dating. The base of the succession consists of a till, capped with a rubefied Eemian palaeosol. It is overlain by a colluvial layer and by a thick loess unit, including three chernozem palaeosols, formed during MIS 4 and 3. The sequence is capped and preserved by fluvioglacial and glacial deposits (MIS 2). Grain-size analysis of each single sand and silt fraction from the loess reveals that it can be used as a proxy of wind energy with higher amounts of coarser fractions corresponding to stronger winds; grain-size zones are identified showing cycles of variations in aeolian dynamics. Chernozems occur at grain-size zone boundaries, corresponding to changes in wind strength. Among heavy minerals, the ultradense fraction also represents a wind proxy, fitting with the identified grain-size zones, higher percentages indicating higher wind intensities. Although the Val Sorda sediments have the same provenance, the glacial and aeolian units are characterized by different heavy mineral assemblages. The loess unit is marked by the presence of garnet, while in both tills amphiboles are common. Magnetic parameters here considered confirm their role of palaeoclimatic proxies, similarly to that proposed for many loess sequences: MS and ARM values fit with the identified grain-size zones; higher values correspond to higher wind intensities. χfd% is sensitive to ultrafine SP particles, confirming its role as a pedogenesis proxy.