Age, formation and significance of loess deposits in central Sweden

Abstract

Loess deposits are common in the mid-latitudes and are excellent records of past climate, landscape change and dust. However, loess deposits are seldom reported from Fennoscandia. Here we investigate two former glaciofluvial areas in central Sweden, Brattforsheden and Bonäsheden, where post-glacial loess and sand dune activity have been documented previously. Based on detailed mapping, grain size, scanning electron microscopy and optically stimulated luminescence dating analyses, we confirm the presence of loess deposits at the sites and extend the known area of loess coverage. Our results suggest that loess deposits are more common than previously thought in Sweden. The results also demonstrate that basal parts of the loess are often mixed with underlying sediment, which may be a common feature of thin loess deposits close to former ice margins. Quartz luminescence is well suited for dating these deposits, but ages from the mixed basal loess layers are older than expected, while ages from undisturbed loess extend to c. 5 ka. The loess ages contrast with the timing of main dune activity in these areas, which is dominantly in the 1-3 kyr postdeglaciation (c. 10.9-10.5 cal kyr BP). We suggest that either sediment mixing during soil formation is responsible for the mid-Holocene loess ages, or that the loess deposits record periodic landscape destabilization into the mid-Holocene. Furthermore, there is a clear topographic control on aeolian sedimentary facies, with loess mantling high ground and dunes restricted to valleys. Loess deposits are also primarily found to the south and southwest of source areas, implying transport from the north and east. This pattern contrasts with evidence for NW winds inferred from associated sand dunes. At present, the reasons for this mismatch are unclear, although one possible explanation is that silts deposited at higher elevations were affected by Ekman flow deflection of NW surface winds.

Storm chasing: Tracking Holocene storminess in southern Sweden using mineral proxies from inland and coastal peat bogs

“…The sampling sites were selected based on available maps, which are low resolution in comparison to the size of the actual deposits. While loess has not been mapped in the area, the low median grain size of AS01 suggests that it could be present, as found in other inland dune systems in Sweden (Alexanderson and Fabel, 2015;H€ orner, 1927;Stevens et al, 2022). The SMT1 samples have a slightly tighter range of median values (with perhaps the exception of SMT1-0) than the samples taken to the west of the bog, which could reflect a more heterogenous landscape cover.…”

Combined optically stimulated luminescence and radiocarbon dating of aeolian dunes in Arctic Sweden

“…This may be due to the denser, more extensive vegetation cover in more southern sites. Interestingly though, coarse silt loess sediments in Värmland in central Sweden also suggest prolonged aeolian activity well into the Middle Holocene, 70 in contrast to the majority of dune ages from the region, 13 implying that aeolian activity throughout Fennoscandia may be episodic in the Holocene.…”