2021
A 1.9 Ga glacial sedimentary-facies association at low palaeolatitude in the Bergslagen Group, Grythyttan Field, Central Sweden
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Glacial sedimentary facies are recognised in the Palaeoproterozoic (Orosirian) Bergslagen Group in central Sweden, described previously as post-orogenic conglomerates in the Grythyttan Field. The evidence is provided by the presence of macro boulders in a megaclastic to conglomerate rock formation or diamictite around lake Brunnsjön, south of Grythyttan. Pebble to cobble size
conglomerates discordantly overlie a megaclastic rock formation, with facetted clasts resembling flatirons. The sedimentary facies assemblage resembles an ice-front resedimented sequence, previously interpreted as an alluvial fan by the writers. A glacial interpretation is supported by evidence of permafrost and related periglacial structures in coeval, 1895 ± 5 Ma (U–Pb zircon age),
metavolcaniclastic rocks in the Bergslagen Group. The association of glacial sedimentary facies, permafrost and banded ironstones in the low-latitudinal Bergslagen Group suggests its similarity to better known ‘Snowball Earth’ deposits from Palaeoproterozoic and particularly Neoproterozoic times.

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