Stable isotope and trace element geochemistry of Upper Cretaceous carbonates and belemnite rostra (Middle Campanian, north Germany) |
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Authors: | Birgit Niebuhr Michael M Joachimski |
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Affiliation: | a Julius-Maximilians-Universität, Institut für Paläontologie, Pleicherwall 1, 97070 Würzburg, Germanyb Universität Erlangen-Nürnberg, Institut für Geologie und Mineralogie, Schlossgarten 5, 91054 Erlangen, Germany |
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Abstract: | Trace element contents and stable isotopic composition of Middle Campanian marl-limestone rhythmites and belemnite rostra of Belemnitella mucronata were investigated. High strontium and low iron as well as manganese and magnesium contents of belemnite calcite and bulk rock samples suggest no diagenetic overprint. However, the orange-coloured cathodoluminescence of coccolith-rich sediments indicates diagenetic cementation and/or recrystallization. The non-luminescent belemnite rostra reveal an extraordinary preservation of the microstructures that is interpreted to have been favoured by a silification of the outer rim of the belemnite rostra. Carbon isotope ratios of the coccolith limestones and belemnite rostra are comparable, with higher δ13C variations observed for belemnite calcite. The 1.5-2‰ depletion in δ18O of the marl-limestone rhythmites relative to belemnite calcite is explained by diagenetic alteration of the sediments. Palaeotemperatures, calculated from the δ18O values of the well-preserved belemnite rostra, are around 12.5 ± 2 °C and suggest rather low sea-surface temperatures for the Middle Campanian epicontinental sea of north Germany assuming a water depth of less than 100 m. |
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Keywords: | Upper Cretaceous North Germany Carbon and oxygen isotopes Belemnites Palaeotemperatures Carbonate diagenesis |
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