Late Weichselian and Holocene climatic and local controls on aeolian deposition inferred from decomposing grain size-shape distributions

Aeolian deposits form rich archives of climatic and environmental changes, which have not been fully explored. In this study, results from end-member modelling of grain size-shape distributions were combined with palynological records to reconstruct sedimentary environments and transport mechanisms, and to distinguish climatically-caused from local or system-intrinsic variabilities. We compare results from Weichselian aeolian type locality Lutterzand in the Eastern Netherlands to those of a aeolian site in the Central Netherlands. Four grain size-shape end-members were determined. These represent coarse fluvial or aeolian bedload, fine aeolian bedload, aeolian modified saltation and aeolian suspension (loess) transport mechanisms. We assume that synchronous changes in end-member composition at the two sites are effects of climate change; non-synchronous changes are the result of local or system-intrinsic variability, which are attributed to the influence of the paleo-topographic position on local humidity of the sediment bed. Our results show that during the final stage of the Late Pleniglacial, a change from polar desert to wet sand-sheet paleo-environment occurred, which implies increased humidity and decreased wind speed that may be linked to a northward shift of the polar front preceding warming during the Bølling time interval. The deposition of loess during the Bølling implies further climate amelioration and a concomitant increase in vegetation density. The landscape re-opens during the Older Dryas. The high degree of sediment sorting and near absence of modified saltation and suspension transport mechanisms/end members during this phase are indicative of an undulating aeolian topography and the formation of incipient dunes, for which sparse vegetation forms growth nuclei. A high loess content reveals that the Betula phase of the Allerød was humid. The subsequent Allerød Pinus phase was drier, potentially due to Pinus-induced drought and wildfires. The deposits of the Younger Dryas reflect a paleo-environment similar to that of the Older Dryas. Land use-induced sand-drifting in the Middle Ages is differentiated from the Late-Weichselian aeolian depositional phases by a higher proportion of suspension and modified saltation end members, reflecting wetter climate and denser vegetation during the Holocene.