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

Guido Meinhold,Arzu Arslan,Teodoro Palacios,Magne Høyberget,Nick M W Roberts,Jan Ove R Ebbestad,Anette E S Högström,Wendy L Taylor,Heda Agić,Sören Jensen

doi:10.1017/s0016756820000564

Abstract

AbstractResults 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.

Highlights

Calcite U–Pb geochronology has attracted increasing interest in recent years within the Earth Sciences community
In the present case study, we focus on calcite from carbonates of the upper Ediacaran – lower Cambrian Manndrapselva Member of the Stáhpogieddi Formation (Vestertana Group, Gaissa Nappe Complex) of the Digermulen Peninsula in eastern Finnmark, Arctic Norway (Fig. 1)
We applied in situ U–Pb dating of calcite using LA-ICP-MS to address this question

Summary

Introduction

Calcite U–Pb geochronology has attracted increasing interest in recent years within the Earth Sciences community. Rasbury & Cole, 2009; Yokoyama et al 2018; Drost et al 2019) and mineralization along fracture and fault planes (e.g. Roberts & Walker, 2016; Goodfellow et al 2017; Nuriel et al 2017; Parrish et al 2018; Holdsworth et al 2019), among others. Regardless of the successful application of calcite U–Pb geochronology in recent years, the method has its challenges. The in situ technique, laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), helps overcome some of these challenges, namely by allowing for the measurement of discrete zones of uranium enrichment that are typical of diagenetic and hydrothermal calcite (Roberts et al 2020), and by allowing a combination of U–Pb analysis with other in situ petrographic and analytical techniques

Methods

Results

Discussion

Conclusion