Thin loess in Southwestern Sweden

ABSTRACT

A thin (20–80 cm), patchy layer of silt-rich sediment occurs at the surface throughout Svartedalen, a nature reserve 30 km north of Gothenburg, Sweden. This surface silt mantles a bedrock-dominated, fracture-valley landscape. Using data from grain-size analysis, OSL dating and detrital-zircon U-Pb dating, we argue that the silt is loess sourced from glacial sediment that was eroded from local bedrock. The sediment has a grain-size distribution typical of wind-blown silt and is especially similar to thin deposits of loess overlying coarser material. OSL ages on five samples range from 1 to 8 ka, although analysis of equivalent dose distributions of one may suggest an age as old as 11 ka. The dates may represent true depositional ages and represent several Holocene eolian events. However, we consider as more likely that the loess was deposited during deglaciation, and quartz-grain signals have been partially reset during bioturbation. U-Pb ages on 273 zircon grains from the loess show prominent peaks at 1.6 and 1.8 Ga, as well as smaller numbers of grains from 1.0 to 1.6 Ga. These ages match dates from the Idefjord Terrane which comprises the bedrock of the study area. We argue that during ice-margin retreat, debris in the glacier was dominated by locally derived debris. This glacial sediment was left in thin patches uplands and particularly in large ice-marginal deltas. These deposits served as the proximal source for the loess. The presence of thin loess in Svartedalen suggests loess to be common in soils of southwest Sweden.

KEYWORDS:

• Computer virus propagation
• SEIRQ model
• Levenberg Marquardt backpropagation
• MSE
• artificial neural networks

Acknowledgements

We thank Birgitta Svensson for her gracious interest in continuing her research, and to Per Wedel, who originally suggested the project to Birgitta. We thank Tore Påsse for information on potential outcrops. Vanda Jakabova was of extremely valuable help in assisting grain-size analysis in Uppsala. We thank David Grimley for information on the Peoria Loess and Sten Ekman for informing us about the Engelke thesis. We thank Randy Schaetzl and an anonymous reviewer for improving this manuscript with their reviews. TS and YB acknowledge funding from the Swedish Research Council (2017-03888) and the Geological Survey of Sweden (6-1857/2020). Funding for AH, FE and MJ was provided by the Department of Earth Sciences, Gothenburg University. This work is the result of a master’s thesis by AH and FE (Ekström & Hedeving, 2021) that was suggested by MJ. AH and FE conducted all fieldwork; AH, FE and MJ wrote the manuscript with additions by HA and YB on dating and provenance. All authors critically read and commented on the manuscript.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by Geological Survey of Sweden: [Grant Number 6-1857/2020]; Swedish Research Council: [Grant Number 2017-03888].