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.
Original language | English |
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Pages (from-to) | 169-177 |
Number of pages | 9 |
Journal | Permafrost and Periglacial Processes |
Volume | 32 |
Issue number | 1 |
Early online date | 17 Dec 2020 |
DOIs | |
Publication status | Published - Jan 2021 |
Funding
G.K., F.F.B. and F.M.vdW. acknowledge funding for fieldwork and laboratory costs from the Dutch Dr. Schürmann Foundation for Precambrian research ( www.dr-schurmannfonds.nl ). The ANWB is thanked for allowing the use of the photograph in Figure 5 . The authors are very grateful for the constructive comments provided by Anthony M. Spencer and Cunhai Gao and two anonymous reviewers.
Funders | Funder number |
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Schürmann Foundation for Precambrian research |
Keywords
- Central Sweden, early Proterozoic, ice-wedge cast, paleo-permafrost