Evidence of permafrost in the Paleoproterozoic (c. 1.9 Ga) of Central Sweden

Abstract

This paper reports on an ice‐wedge pseudomorph that formed and is preserved in metavolcanic host material that was later transformed to metamorphic solid bedrock. It has been dated to 1,895 ± 5 Ma by U–Pb geochronology of zircon in the bedrock, an Early Proterozoic age. Detailed observation of the deformation structures of the wedge points to an ice‐wedge pseudomorph based on typical downbending around the wedge and vertical lamination in the inner part of the wedge due to slumping into the wedge after the ice melted, along with a few remains of lateral pressure structures (such as folds and upturned strata) in the adjacent host sediment. The interpretation of the wedge structure as an ice‐wedge pseudomorph confirms previous work on this topic. This ice‐wedge pseudomorph demonstrates for the first time the existence of permafrost at c. 1.9 Ga. It indicates that permafrost and associated conditions were present in lowlands at low latitude at discrete time intervals early in Earth’s history. Although some caution should be applied, mean annual air temperature appears to have been slightly below the freezing point at that time.

The Fagervik diamictite: Evidence for a low-latitude, post-1871 Ma glaciation in the Svecofennian orogen of northern Sweden

“…The missing link is provided by Fennoscandian and other BIFs of that age and glacial evidence from central and northern Sweden (Kuipers et al, 2013(Kuipers et al, , 2021Vandenberghe et al, 2020;herein) and from the Kimberley basin of NW Australia (Williams, 2005).…”

“…There is mounting evidence for a post-1900 Ma glaciation from the Palaeoproterozoic Bergslagen province in central Sweden (Kuipers et al, 2013(Kuipers et al, , 2018(Kuipers et al, , 2021Vandenberghe et al, 2020). Although the accretionary (exotic) nature of the Skelleftea field and Bergslagen requires caution, existing paleomagnetic data from various locations within the Svecofennian orogen indicate an equatorial latitude for formation of the periglacial structures and glacial deposits, reminiscent of the Neoproterozoic 'Snowball Earth' period.…”

The Fagervik diamictite: Evidence for a low-latitude, post-1871 Ma glaciation in the Svecofennian orogen of northern Sweden

“…The missing link is provided by Fennoscandian and other BIFs of that age and glacial evidence from central and northern Sweden (Kuipers et al, 2013(Kuipers et al, , 2021Vandenberghe et al, 2020;herein) and from the Kimberley basin of NW Australia (Williams, 2005).…”

“…There is mounting evidence for a post-1900 Ma glaciation from the Palaeoproterozoic Bergslagen province in central Sweden (Kuipers et al, 2013(Kuipers et al, , 2018(Kuipers et al, , 2021Vandenberghe et al, 2020). Although the accretionary (exotic) nature of the Skelleftea field and Bergslagen requires caution, existing paleomagnetic data from various locations within the Svecofennian orogen indicate an equatorial latitude for formation of the periglacial structures and glacial deposits, reminiscent of the Neoproterozoic 'Snowball Earth' period.…”