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.

中文翻译：

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古代碳酸盐中方解石的 U-Pb 测年用于同沉积后过程的年龄估计：来自挪威北极芬马克上埃迪卡拉纪地层的案例研究

报告了来自挪威北极芬马克上埃迪卡拉纪钙质结核的方解石球晶、锥形 (CIC) 方解石和方解石纤维的原位 U-Pb 测年结果。来自结核最内层的方解石球晶产生的截距较低，为 563 ± 70 Ma，虽然不精确，但在基于化石组合的沉积年龄的不确定性范围内。来自结核底部的未变形 CIC 方解石的年龄为 475 ± 25 Ma，这被解释为在沉积物埋藏期间引起的流体超压期间 CIC 方解石形成的年龄。来自结核顶部的变形 CIC 方解石产生的年龄为 418 ± 23 Ma，与已知的加里东构造变质事件重叠，并表示此时可能存在沉积后叠印。沿着球晶边缘在小裂缝中生长的方解石纤维被解释为变形和形成解理过程中的再结晶特征，给出了 486 ± 161 Ma 的不精确年龄。我们的研究结果表明，方解石的 U-Pb 测年可以为古代碳酸盐岩和在埋藏和变质叠印期间运行的沉积后过程提供年龄限制。