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A geochemical interpretation of sediment maturity and weathering, provenance, palaeoclimate, tectonic setting and redox-sensitive proxies is broadly assessed across the late Ediacaran‒Terreneuvian arc to rift turnover preserved in the Iberian Massif, based on major, trace and rare earth elements. Chemical concentrations of 393 (granulometric) shale, greywacke and very fine-grained sandstone samples (geochemically assigned to shale and wacke compositions), taken from bibliographic sources (from the Ossa-Morena, Central Iberian, West Asturian–Leonese and Cantabrian Zones and the Iberian Chains), were completed with 37 new terrigenous samples from the Cíjara Formation and carbonate ones from the Ibor Group (Central Iberian Zone). The REEs are mainly characterized by slight enrichment in LREEs and loss of HREEs (with LREE/HREE ratios ranging from 4.3 to 18.9; average 8.3). The values of (La/Yb)N are 0.4 to 1.2 (average 0.8) and those of (Gd/Yb)N 4.3 to 18.9 (average 0.98) indicating variable patterns of fractionation of LREE and HREE. Sedimentary provenance from bivariate plots of Zr versus TiO2, La/Sc versus Th/Sc, Sc versus Th/Sc, Hf versus La/Th shows that despite the arc to rift turnover, all the samples persistently derived from felsic igneous and quartzose sedimentary sources, with subsidiary intermediate and mafic igneous influences. The discrimination diagrams of source areas (Th–Co–Zr/10, Th–Sc–Zr/10 and La–Th–Sc) suggest that the sedimentary rocks were originally deposited in Cadomian-related continental island-arc settings, succeeded by recycling of rift basement-inherited uplifted shoulders. Semi-arid climates, represented by Al2O3 + Fe2O3 + MgO + CaO + Na2O + K2O versus SiO2 and Sr/Cu versus Ga/Rb plots, seemingly prevailed, although some geochemical indicators of source weathering may have also been chemically mimicked by burial diagenesis. Redox proxies (Pr/Pr*SN vs Ce/Ce*SN and Ti vs ΣREE plots) yielded by impure carbonate interbeds from the Ibor Group indicate carbonate production under oxic, suboxic and anoxic substrates, the latter related to carbonate factories developed along the retroarc foredeep basin and associated in the Salamanca-Hurdes Dome with black (kerogenous) shales.

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Geochemical (Non-Isotopic) Proxy Indicators of the Late Ediacaran‒Terreneuvian Arc to Rift Turnover in the Iberian Massif, Spain

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  • 发表日期：

    2026年

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  • J. J. Álvaro

摘要

A geochemical interpretation of sediment maturity and weathering, provenance, palaeoclimate, tectonic setting and redox-sensitive proxies is broadly assessed across the late Ediacaran‒Terreneuvian arc to rift turnover preserved in the Iberian Massif, based on major, trace and rare earth elements. Chemical concentrations of 393 (granulometric) shale, greywacke and very fine-grained sandstone samples (geochemically assigned to shale and wacke compositions), taken from bibliographic sources (from the Ossa-Morena, Central Iberian, West Asturian–Leonese and Cantabrian Zones and the Iberian Chains), were completed with 37 new terrigenous samples from the Cíjara Formation and carbonate ones from the Ibor Group (Central Iberian Zone). The REEs are mainly characterized by slight enrichment in LREEs and loss of HREEs (with LREE/HREE ratios ranging from 4.3 to 18.9; average 8.3). The values of (La/Yb)N are 0.4 to 1.2 (average 0.8) and those of (Gd/Yb)N 4.3 to 18.9 (average 0.98) indicating variable patterns of fractionation of LREE and HREE. Sedimentary provenance from bivariate plots of Zr versus TiO2, La/Sc versus Th/Sc, Sc versus Th/Sc, Hf versus La/Th shows that despite the arc to rift turnover, all the samples persistently derived from felsic igneous and quartzose sedimentary sources, with subsidiary intermediate and mafic igneous influences. The discrimination diagrams of source areas (Th–Co–Zr/10, Th–Sc–Zr/10 and La–Th–Sc) suggest that the sedimentary rocks were originally deposited in Cadomian-related continental island-arc settings, succeeded by recycling of rift basement-inherited uplifted shoulders. Semi-arid climates, represented by Al2O3 + Fe2O3 + MgO + CaO + Na2O + K2O versus SiO2 and Sr/Cu versus Ga/Rb plots, seemingly prevailed, although some geochemical indicators of source weathering may have also been chemically mimicked by burial diagenesis. Redox proxies (Pr/Pr*SN vs Ce/Ce*SN and Ti vs ΣREE plots) yielded by impure carbonate interbeds from the Ibor Group indicate carbonate production under oxic, suboxic and anoxic substrates, the latter related to carbonate factories developed along the retroarc foredeep basin and associated in the Salamanca-Hurdes Dome with black (kerogenous) shales.