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

Since the discovery of the Neoproterozoic 'Snowball Earth' glaciations, the climate history of the Earth in the Precambrian has been in the spotlight more than ever. Here we investigate the ≤1871 Ma old Fagervik diamictite, exposed along the coast of the Bothnian Gulf in northern Sweden, on the Fennoscandian Shield. Previously described as a magmatic, hydraulic breccia, we reinterpret this deposit as a subglacial, deformed till, based on syndepositional textures, particularly the imprint of significant crushing and bedding-parallel shearing. A greenschist-facies metamorphic overprint affected the matrix mineralogy, but preserved characteristic synsedimentary macro- and microtextures. The diamictite formed near sea-level most likely at low geographical latitude. This would be a second account of a glacigenic deposit from the late Palaeoproterozoic era in Sweden, following evidence for ~1895 Ma periglacial and proglacial sedimentary rocks in Bergslagen, South central Sweden.

Deposition of Precambrian Banded Iron Formations (BIFs) was commonly associated with glaciations, but for 1.9–1.8 Ga BIFs the correlation was less evident. The Fagervik diamictite adds additional evidence for the glacial connection of BIFs.