Die Bildung von Mega-Glendoniten nach dem Paläozän-Eozän Temperaturmaximum
Zusammenfassung der Projektergebnisse
The Early Eocene Fur Formation of Northwestern Denmark comprises the world-wide largest, glendonites (CaCO3), a calcite pseudomorph after the metastable mineral ikaite (CaCO3•6H2O). Several authors used glendonites as an indicator for cold times in the geologic record, but the Early Eocene is known for its warm climate following the Paleocene- Eocene Thermal Maximum (PETM). The mega-glendonites of Fur Formation were investigated for their geochemical composition in order to decipher the paleoenvironmental conditions during ikaite formation in the Early Eocene. Several temperature proxies (Δ47; δ18Ocarb; δ18Odiatom) were applied to unravel the thermal history of ikaite formation in the silicadominated, carbonate-free, and organic-rich Danish Basin. The reconstruction of paleotemperatures within the sedimentary column points to cold bottom water temperatures during ikaite formation. For the first time it was possible to derive clumped isotope (Δ47) temperatures from the first calcite phase of ikaite recrystallization (replacive calcite). The results indicate a range of +5 to +6 °C for the temperature of transformation from ikaite to glendonite while even lower temperatures are suggested by carbonate oxygen isotopes for the non-glendonite bearing carbonate concretion horizons. Consequently, low temperatures have to be regarded as a possible control on ikaite formation in addition to high organic matter content, high phosphate concentration and possibly a methane contribution leading to anaerobic oxidation of methane (AOM). The glendonites of the Fur Formation are mostly encased in carbonate concretions. Additional carbonate concretions occur also in horizons without glendonites. Most of the carbonate concretions and the glendonites are bound to certain ash layers embedded within clayey diatomite. Glendonites are usually found below ash layers of more than 7 cm thickness and with a tholeiitic chemistry. While the results from strontium isotope analyses indicate that the alteration of the ashes is not a significant source of strontium during ikaite formation, the ash layers might have served as important lateral fluid conduits triggering ikaite formation. Other geochemical parameters give insight into e.g. the biogeochemical process responsible for carbonate formation. Biomarker show that in the lower part of Fur Formation (Knudeklint Member) methanogenesis lead to the formation of carbonates (ankerite, dolomite). The main process is however organotrophic sulfate reduction. While the carbon isotopic composition of the glendonites could be pointing to organic matter as well as to methane as carbon source, the results from carbonate associated sulfate (CAS) point towards a distinct contribution of methane. Finally, a paleoenvironmental model was developed for the deposition of the Early Eocene Fur Formation in order to reconstruct the conditions for the formation of ikaite and its subsequent transformation to glendonite in the sediments.
Projektbezogene Publikationen (Auswahl)
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(2014) The role of temperature in the formation of mega-glendonites in the aftermath of the Paleocene-Eocene Thermal Maximum. GDGT-based proxies: state of the art and future directions, workshop, NIOZ, Texel, Netherlands
Nenning, F., Teichert, B.M.A., Madsen, H., Schultz, B.P.
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Glendonite formation at methane seeps – Biogeochemical or temperature control. GSA Vancouver, Canada, 2014
Teichert, B.M.A.
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Glendonites as archives of paleoenvironmental change in the aftermath of the PETM. Goldschmidt Abstracts, Prague, Czech Republic, 2015, 2255
Nenning, F., Teichert, B.M.A., Gussone, N., Schultz, B.P., Birgel, D., Peckmann, J., Strauß, H.
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(2016) Glendonites and geochemistry. UNESCO World Heritage and Symposium. Roslev, Denmark
Nenning, F., Teichert, B.M.A., Strauß, H., Gussone, N., Birgel, D., Peckmann, J., Schultz, B.P., Madsen, H.
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(2017) Mega-glendonites in the Early Eocene Fur Formation – Unraveling paleoenvironmental conditions in the Danish Basin and their influence on glendonite formation. Dissertation Westfälische Wilhelms-Universität Münster, pp. 162
Nenning, F.
