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U-Pb dating of calcite in ancient carbonates for age estimates of syn- to post-depositional processes: a case study from the upper Ediacaran strata of Finnmark, Arctic Norway

U-Pb dating of calcite in ancient carbonates for age estimates of syn- to post-depositional processes: a case study from the upper Ediacaran strata of Finnmark, Arctic Norway Thumbnail


Abstract

Results of in situ U-Pb dating of calcite spherulites, cone-in-cone (CIC) calcite and calcite fibres from a calcareous concretion of the upper Ediacaran of Finnmark, Arctic Norway, are reported. Calcite spherulites from the innermost layers of the concretion yielded a lower intercept age of 563 ± 70 Ma, which although imprecise, is within uncertainty of the age of sedimentation based on fossil assemblages. Non-deformed CIC calcite from the bottom part of the concretion yielded an age of 475 ± 25 Ma, which is interpreted as the age of CIC calcite formation during a period of fluid overpressure induced during burial of the sediments. Deformed CIC calcite from the top part of the concretion yielded an age of 418 ± 23 Ma, which overlaps with a known Caledonian tectono-metamorphic event, and indicates a potential post-depositional overprint at this time. Calcite fibres that grew in small fissures along spherulite rims, which are interpreted as a recrystallization feature during deformation and formation of a cleavage, gave an imprecise age of 486 ± 161 Ma. Our results show that U-Pb dating of calcite can provide age constraints for ancient carbonates and syn- to postdepositional processes that operated during burial and metamorphic overprinting.

Acceptance Date May 11, 2020
Publication Date Jul 11, 2020
Publicly Available Date Mar 28, 2024
Journal Geological Magazine
Print ISSN 0016-7568
Publisher Cambridge University Press
Pages 1367-1372
DOI https://doi.org/10.1017/S0016756820000564
Keywords U–Pb calcite geochronology; calcite spherulites; cone-in-cone calcite; Ediacaran; Caledonides; Norway
Publisher URL https://doi.org/10.1017/S0016756820000564

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