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

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 post-depositional processes that operated during burial and metamorphic overprinting.

Rare earth elements and neodymium and strontium isotopic constraints on provenance switch and post-depositional alteration of fossiliferous Ediacaran and lowermost Cambrian strata from Arctic Norway

“…TIB -Transscandinavian Igneous Belt. calcite U-Pb age of 418 ± 23 Ma from deformed cone-in-cone calcite within the 2nd cycle of the Manndrapselva Member on the Digermulen Peninsula (Meinhold et al, 2020). It also overlaps in error with a Rb-Sr age of 430 ± 11 Ma from the<0.1 μm grain-size fraction from the Indreelva Member of the parautochthonous units on the Varanger Peninsula (Gorokhov et al, 2001).…”

“…3). The postdepositional low-grade metamorphic overprint of the sedimentary succession of the Digermulen Peninsula is related to a Scandian tectonometamorphic event at 450-430 Ma (Meinhold et al, 2019b(Meinhold et al, , 2020.…”

“…Our 147 Nd isotopic data provide the first constraints on provenance changes across a glacial-interglacial cycle and the fossil-bearing Ediacaran-Cambrian boundary interval in Scandinavia. Results from the 87 Rb-87 Sr whole-rock isochron method (this study) are compared with previously obtained ages for the metamorphic overprint based on finefraction 40 K-40 Ar (Meinhold et al, 2019b) and in situ 238,235 U-206,207 Pb calcite data (Meinhold et al, 2020). Finally, we explore how redox-sensitive elements (primarily Ce) in the Digermulen succession relate to the stratigraphical distribution of palaeopascichnids and Ediacara-type fossils.…”

Geochronological and geochemical constraints on the origin of highly 13Ccarb-depleted calcite in basal Ediacaran cap carbonate

“…LA-ICP-MS U-Pb dating of carbonates has been applied to material with ages ranging from the Mesoproterozoic to Quaternary, but mostly to the Mesozoic to Cenozoic (see Roberts et al 2020). Because of high ratios of common to radiogenic lead, most older dates reported from Precambrian to Cambrian carbonates (Liivamägi et al 2018(Liivamägi et al , 2021Meinhold et al 2020) are rather imprecise (e.g. 5-12 % uncertainties 2σ).…”

In situ U-Pb Dating of Calcite from the South China Antimony Metallogenic Belt

“…The limitations include: (1) the scarce of spike (e.g. 233 U- 205 Pb) ( Moorbath et al., 1987 ; Pickering et al., 2010 ; Engel et al., 2020 ); (2) low U and Pb contents (<1 ppm) within single hydrothermal carbonate minerals ( Brannon et al., 1996 ; Grandia et al., 2000 ; Coveney et al., 2000 ; Meinhold et al., 2020 ); and (3) a small spread of 238 U/ 206 Pb due to the average of isotopic zonation within the analytical volume ( Li et al., 2014 ; Guillong et al., 2020 ; Roberts et al., 2020 ).…”