Details
| Original language | English |
|---|---|
| Article number | 122795 |
| Journal | Chemical Geology |
| Volume | 684 |
| Early online date | 11 Apr 2025 |
| Publication status | Published - 30 Jun 2025 |
Abstract
Ferromanganese (Fe-Mn) nodules are marine chemical sediments that represent unique archives for the reconstruction of ambient seawater conditions. This record is limited from modern to Cenozoic times due to the instability of Fe-Mn oxides during burial and subduction of the oceanic crust and overlying sediments. However, almost uncharacterized Fe-Mn nodules exist in Jurassic sedimentary strata throughout the ancient Tethyan region approximately 100 Ma older than the oldest yet-investigated Cenozoic nodules. Their reliability as geochemical archives for the reconstruction of ancient seawater is, however, poorly understood. In this study, Fe-Mn nodules from the Pyhrntal area (Austria) are geochemically and mineralogically characterized and subdivided into four types with variable amounts of carbonates (calcite, rhodochrosite), todorokite, and hematite as major phases. Shale-normalized rare earth element and yttrium systematics of all types indicate a hydrogenetic origin with characteristic positive Ce anomalies and negative Y anomalies. In-situ Fe isotope measurements of the Fe-Mn nodules display a δ 56/54Fe range between −0.32 and −0.02 ‰ for the Jurassic Tethyan Ocean, similar to values from modern Atlantic nodules. Stable Mo (δ 98/95Mo = −0.97 to −0.56 ‰) and U (δ 238/235U = −0.75 to −0.47 ‰) isotope compositions resemble those of modern and Cenozoic Fe-Mn nodules, suggesting that Middle Jurassic oceans were similarly well‑oxygenated as modern oceans. Our results demonstrate the reliability of fossil Fe-Mn nodules in the Pyhrntal as geochemical archives for the composition of paleo-seawater, encouraging the investigation of other ancient Fe-Mn deposits which may significantly improve and complement the picture of the redox evolution of Phanerozoic oceans.
Keywords
- Fe-Mn nodules, Rare earth elements, Redox evolution, Seawater, Tethys, U-Mo-Fe isotopes
ASJC Scopus subject areas
- Earth and Planetary Sciences(all)
- Geology
- Earth and Planetary Sciences(all)
- Geochemistry and Petrology
Sustainable Development Goals
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In: Chemical Geology, Vol. 684, 122795, 30.06.2025.
Research output: Contribution to journal › Article › Research › peer review
}
TY - JOUR
T1 - The stable U-Mo-Fe isotope records of Middle Jurassic hydrogenetic ferromanganese deposits
AU - Klamt, Viona
AU - Kraemer, Dennis
AU - Fernandez, Oscar
AU - Horn, Ingo
AU - Hohl, Simon V.
AU - Weyer, Stefan
AU - Viehmann, Sebastian
PY - 2025/6/30
Y1 - 2025/6/30
N2 - Ferromanganese (Fe-Mn) nodules are marine chemical sediments that represent unique archives for the reconstruction of ambient seawater conditions. This record is limited from modern to Cenozoic times due to the instability of Fe-Mn oxides during burial and subduction of the oceanic crust and overlying sediments. However, almost uncharacterized Fe-Mn nodules exist in Jurassic sedimentary strata throughout the ancient Tethyan region approximately 100 Ma older than the oldest yet-investigated Cenozoic nodules. Their reliability as geochemical archives for the reconstruction of ancient seawater is, however, poorly understood. In this study, Fe-Mn nodules from the Pyhrntal area (Austria) are geochemically and mineralogically characterized and subdivided into four types with variable amounts of carbonates (calcite, rhodochrosite), todorokite, and hematite as major phases. Shale-normalized rare earth element and yttrium systematics of all types indicate a hydrogenetic origin with characteristic positive Ce anomalies and negative Y anomalies. In-situ Fe isotope measurements of the Fe-Mn nodules display a δ 56/54Fe range between −0.32 and −0.02 ‰ for the Jurassic Tethyan Ocean, similar to values from modern Atlantic nodules. Stable Mo (δ 98/95Mo = −0.97 to −0.56 ‰) and U (δ 238/235U = −0.75 to −0.47 ‰) isotope compositions resemble those of modern and Cenozoic Fe-Mn nodules, suggesting that Middle Jurassic oceans were similarly well‑oxygenated as modern oceans. Our results demonstrate the reliability of fossil Fe-Mn nodules in the Pyhrntal as geochemical archives for the composition of paleo-seawater, encouraging the investigation of other ancient Fe-Mn deposits which may significantly improve and complement the picture of the redox evolution of Phanerozoic oceans.
AB - Ferromanganese (Fe-Mn) nodules are marine chemical sediments that represent unique archives for the reconstruction of ambient seawater conditions. This record is limited from modern to Cenozoic times due to the instability of Fe-Mn oxides during burial and subduction of the oceanic crust and overlying sediments. However, almost uncharacterized Fe-Mn nodules exist in Jurassic sedimentary strata throughout the ancient Tethyan region approximately 100 Ma older than the oldest yet-investigated Cenozoic nodules. Their reliability as geochemical archives for the reconstruction of ancient seawater is, however, poorly understood. In this study, Fe-Mn nodules from the Pyhrntal area (Austria) are geochemically and mineralogically characterized and subdivided into four types with variable amounts of carbonates (calcite, rhodochrosite), todorokite, and hematite as major phases. Shale-normalized rare earth element and yttrium systematics of all types indicate a hydrogenetic origin with characteristic positive Ce anomalies and negative Y anomalies. In-situ Fe isotope measurements of the Fe-Mn nodules display a δ 56/54Fe range between −0.32 and −0.02 ‰ for the Jurassic Tethyan Ocean, similar to values from modern Atlantic nodules. Stable Mo (δ 98/95Mo = −0.97 to −0.56 ‰) and U (δ 238/235U = −0.75 to −0.47 ‰) isotope compositions resemble those of modern and Cenozoic Fe-Mn nodules, suggesting that Middle Jurassic oceans were similarly well‑oxygenated as modern oceans. Our results demonstrate the reliability of fossil Fe-Mn nodules in the Pyhrntal as geochemical archives for the composition of paleo-seawater, encouraging the investigation of other ancient Fe-Mn deposits which may significantly improve and complement the picture of the redox evolution of Phanerozoic oceans.
KW - Fe-Mn nodules
KW - Rare earth elements
KW - Redox evolution
KW - Seawater
KW - Tethys
KW - U-Mo-Fe isotopes
UR - http://www.scopus.com/inward/record.url?scp=105002655032&partnerID=8YFLogxK
U2 - 10.1016/j.chemgeo.2025.122795
DO - 10.1016/j.chemgeo.2025.122795
M3 - Article
VL - 684
JO - Chemical Geology
JF - Chemical Geology
SN - 0009-2541
M1 - 122795
ER -