Geodynamic seawater-sediment porewater evolution of the east central Atlantic Paleogene ocean margin revealed by U-Pb dating of sedimentary phosphates
Emerging evidence suggests that U-Pb and Lu-Hf ages of sedimentary apatite group minerals are often younger than their biostratigraphic ages. However, U-Pb dating of exquisitely preserved carbonate fluorapatite (CFA) is rare. The Upper Cretaceous/Paleogene marine sedimentary rocks of the Moroccan Hi...
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Frontiers Media S.A.
2022-09-01
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| Series: | Frontiers in Earth Science |
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| Online Access: | https://www.frontiersin.org/articles/10.3389/feart.2022.997008/full |
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| author | Jérémie Aubineau Fleurice Parat Ernest Chi Fru Radouan El Bamiki Olivia Mauguin Fabien Baron Marc Poujol Michel Séranne |
| author_facet | Jérémie Aubineau Fleurice Parat Ernest Chi Fru Radouan El Bamiki Olivia Mauguin Fabien Baron Marc Poujol Michel Séranne |
| author_sort | Jérémie Aubineau |
| collection | DOAJ |
| description | Emerging evidence suggests that U-Pb and Lu-Hf ages of sedimentary apatite group minerals are often younger than their biostratigraphic ages. However, U-Pb dating of exquisitely preserved carbonate fluorapatite (CFA) is rare. The Upper Cretaceous/Paleogene marine sedimentary rocks of the Moroccan High Atlas host phosphate-rich sediments bracketed by calcareous nannofossil Zones (NP4-NP9) of late Danian to Thanetian age. Here, we use a laser-ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) to decipher whether CFA minerals are suitable for U-Pb chronostratigraphy and whether they can reveal the sedimentary and seawater history from which they formed. U-Pb dating of the CFA grains yields ages of 42.9 ± 1.3 Ma (MSWD = 2.3) and 35.7 ± 2.8 Ma (MSWD = 1.3) from three distinct phosphate-rich beds, being >15 million years younger than the expected biostratigraphic age. Combined scanning electron microscopy, X-ray diffraction, and infrared spectroscopy analyses, associate the Mg-rich clay minerals sepiolite and palygorskite, with micro-CFA crystals, while LA-ICP-MS trace element, rare earth element, and yttrium content for primary CFA grains, collectively point to long-term early diagenetic adsorption from oxygenated seawater-dominated porewater fluids. Authigenic clay minerals display a seawater-like pattern, with negligible U concentrations suggesting limited clay mineral influence on U-Pb dating of the CFA crystals. Considering the absence of extensive post-depositional alteration, we propose that because of their large surface area, the µm-sized CFA crystallites facilitated real-time surface adsorption and desorption of elements and diffusion processes. These conditions generated long-term open system connection of sediments with overlying seawater, enabling continuous U-Pb exchange for 15–25 Myr after phosphate precipitation. The data suggest that system closure was potentially associated with sediment lithification and the Atlas orogeny, pointing to stable oxygenation of shallow marine waters along the eastern passive margin of the central Atlantic Ocean in the Paleogene. |
| first_indexed | 2024-04-11T21:25:51Z |
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| institution | Directory Open Access Journal |
| issn | 2296-6463 |
| language | English |
| last_indexed | 2024-04-11T21:25:51Z |
| publishDate | 2022-09-01 |
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| spelling | doaj.art-7bce8c7a283444d986084ecf26d54ccd2022-12-22T04:02:25ZengFrontiers Media S.A.Frontiers in Earth Science2296-64632022-09-011010.3389/feart.2022.997008997008Geodynamic seawater-sediment porewater evolution of the east central Atlantic Paleogene ocean margin revealed by U-Pb dating of sedimentary phosphatesJérémie Aubineau0Fleurice Parat1Ernest Chi Fru2Radouan El Bamiki3Olivia Mauguin4Fabien Baron5Marc Poujol6Michel Séranne7Géosciences Montpellier, Université de Montpellier, CNRS UMR 5243, Montpellier, FranceGéosciences Montpellier, Université de Montpellier, CNRS UMR 5243, Montpellier, FranceCenter of Geobiology and Geochemistry, School of Earth and Ocean Sciences, College of Physical Sciences and Engineering, Cardiff University, Cardiff, United KingdomMohammed VI Polytechnic UniversityGeology and Sustainable Mining, Ben Guerir, MoroccoGéosciences Montpellier, Université de Montpellier, CNRS UMR 5243, Montpellier, FranceIC2MP, Université de Poitiers, CNRS UMR 7285, Poitiers, FranceUniv Rennes, CNRS, Géosciences Rennes, UMR 6118, Rennes, FranceGéosciences Montpellier, Université de Montpellier, CNRS UMR 5243, Montpellier, FranceEmerging evidence suggests that U-Pb and Lu-Hf ages of sedimentary apatite group minerals are often younger than their biostratigraphic ages. However, U-Pb dating of exquisitely preserved carbonate fluorapatite (CFA) is rare. The Upper Cretaceous/Paleogene marine sedimentary rocks of the Moroccan High Atlas host phosphate-rich sediments bracketed by calcareous nannofossil Zones (NP4-NP9) of late Danian to Thanetian age. Here, we use a laser-ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) to decipher whether CFA minerals are suitable for U-Pb chronostratigraphy and whether they can reveal the sedimentary and seawater history from which they formed. U-Pb dating of the CFA grains yields ages of 42.9 ± 1.3 Ma (MSWD = 2.3) and 35.7 ± 2.8 Ma (MSWD = 1.3) from three distinct phosphate-rich beds, being >15 million years younger than the expected biostratigraphic age. Combined scanning electron microscopy, X-ray diffraction, and infrared spectroscopy analyses, associate the Mg-rich clay minerals sepiolite and palygorskite, with micro-CFA crystals, while LA-ICP-MS trace element, rare earth element, and yttrium content for primary CFA grains, collectively point to long-term early diagenetic adsorption from oxygenated seawater-dominated porewater fluids. Authigenic clay minerals display a seawater-like pattern, with negligible U concentrations suggesting limited clay mineral influence on U-Pb dating of the CFA crystals. Considering the absence of extensive post-depositional alteration, we propose that because of their large surface area, the µm-sized CFA crystallites facilitated real-time surface adsorption and desorption of elements and diffusion processes. These conditions generated long-term open system connection of sediments with overlying seawater, enabling continuous U-Pb exchange for 15–25 Myr after phosphate precipitation. The data suggest that system closure was potentially associated with sediment lithification and the Atlas orogeny, pointing to stable oxygenation of shallow marine waters along the eastern passive margin of the central Atlantic Ocean in the Paleogene.https://www.frontiersin.org/articles/10.3389/feart.2022.997008/fullcarbonate fluorapatitein situ U-Pb datingMoroccan High AtlasPaleogeneseawater signature |
| spellingShingle | Jérémie Aubineau Fleurice Parat Ernest Chi Fru Radouan El Bamiki Olivia Mauguin Fabien Baron Marc Poujol Michel Séranne Geodynamic seawater-sediment porewater evolution of the east central Atlantic Paleogene ocean margin revealed by U-Pb dating of sedimentary phosphates Frontiers in Earth Science carbonate fluorapatite in situ U-Pb dating Moroccan High Atlas Paleogene seawater signature |
| title | Geodynamic seawater-sediment porewater evolution of the east central Atlantic Paleogene ocean margin revealed by U-Pb dating of sedimentary phosphates |
| title_full | Geodynamic seawater-sediment porewater evolution of the east central Atlantic Paleogene ocean margin revealed by U-Pb dating of sedimentary phosphates |
| title_fullStr | Geodynamic seawater-sediment porewater evolution of the east central Atlantic Paleogene ocean margin revealed by U-Pb dating of sedimentary phosphates |
| title_full_unstemmed | Geodynamic seawater-sediment porewater evolution of the east central Atlantic Paleogene ocean margin revealed by U-Pb dating of sedimentary phosphates |
| title_short | Geodynamic seawater-sediment porewater evolution of the east central Atlantic Paleogene ocean margin revealed by U-Pb dating of sedimentary phosphates |
| title_sort | geodynamic seawater sediment porewater evolution of the east central atlantic paleogene ocean margin revealed by u pb dating of sedimentary phosphates |
| topic | carbonate fluorapatite in situ U-Pb dating Moroccan High Atlas Paleogene seawater signature |
| url | https://www.frontiersin.org/articles/10.3389/feart.2022.997008/full |
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