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<p>In the northwestern (NW) Iberian Peninsula (NW Gondwana) Ordovician black-grey shales and sandstones were deposited on marine platforms at southern polar latitudes. Provenance, recycling, weathering and redox geochemical proxies were derived from the bulk rock composition of siliciclastic rocks recovered from northwest Spain. Statistically significant proxies were studied across the stratigraphy to interpret the paleoenvironment of this region during the Ordovician period. During the beginning of the Middle Ordovician period, the black-grey shales recorded a noticeable influence of recycling and provenance (Th/Sc, Zr/Sc, Zr/Ti, La/Th), and slightly lower levels of chemical alteration (CIA, Th/U) and oxygen conditions (Ce/Ce*, Y/Ho). Evidence for more felsic and recycled sources and possible periglacial-glacial conditions are consistent with the location of the NW Iberian Peninsula at high latitudes close to the South Pole. Towards the upper part of the Middle Ordovician, the black-grey shales recorded less felsic and less recycled sources, possibly associated with a more temperate climate, more chemical alteration, and a relatively more oxygenated environment. Proposed sedimentary models (glacial-arid conditions becoming more temperate, basinal barriers, and/or upwelling basinal waters shifting to more open ocean and stable conditions) can explain these geochemical variations and support the Ordovician paleoenvironmental reconstructions for this part of Gondwana.</p>

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Gondwana platform paleoenvironment reconstruction: insights from the geochemistry of Ordovician black-grey shales in NW Iberia

  • 期刊论文

  • 发表日期：

    2025年4月15日

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  • Alba Lozano,
  • Luis González-Menéndez,
  • Ignacio González-Álvarez,
  • Fernando Gómez Fernández,
  • Pablo Caldevilla

摘要

In the northwestern (NW) Iberian Peninsula (NW Gondwana) Ordovician black-grey shales and sandstones were deposited on marine platforms at southern polar latitudes. Provenance, recycling, weathering and redox geochemical proxies were derived from the bulk rock composition of siliciclastic rocks recovered from northwest Spain. Statistically significant proxies were studied across the stratigraphy to interpret the paleoenvironment of this region during the Ordovician period. During the beginning of the Middle Ordovician period, the black-grey shales recorded a noticeable influence of recycling and provenance (Th/Sc, Zr/Sc, Zr/Ti, La/Th), and slightly lower levels of chemical alteration (CIA, Th/U) and oxygen conditions (Ce/Ce*, Y/Ho). Evidence for more felsic and recycled sources and possible periglacial-glacial conditions are consistent with the location of the NW Iberian Peninsula at high latitudes close to the South Pole. Towards the upper part of the Middle Ordovician, the black-grey shales recorded less felsic and less recycled sources, possibly associated with a more temperate climate, more chemical alteration, and a relatively more oxygenated environment. Proposed sedimentary models (glacial-arid conditions becoming more temperate, basinal barriers, and/or upwelling basinal waters shifting to more open ocean and stable conditions) can explain these geochemical variations and support the Ordovician paleoenvironmental reconstructions for this part of Gondwana.