EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Belemnites, clumped isotopes and oxygen fractionation

Madeleine Vickers1, Stefano Bernasconi2, Clemens Ullmann3, Stephen Hesselbo3, Gregory Price4, and Christoph Korte1
Madeleine Vickers et al.
  • 1University of Copenhagen, Department of Geosciences and Natural Resource Management, Geology Section, Copenhagen K, Denmark (
  • 2ETH Zurich, Geologisches Institut, Sonneggstrasse 5, 8092 Zürich, Switzerland
  • 3Camborne School of Mines, University of Exeter, Penryn Campus, Penryn, Cornwall TR10 9FE, U.K.
  • 4School of Geography, Earth and Environmental Sciences, Plymouth University, Drake Circus, Plymouth, PL4 8AA, U.K.

Belemnite calcite has been used extensively for Jurassic and Cretaceous stable oxygen isotope temperature reconstructions since the 1950s. However, with the advent of clumped isotope thermometry, a consistent offset between reconstructed δ18O temperatures vs Δ47 temperatures from the same belemnites has been observed. We investigate the causes of this offset by analyzing samples from the aragonitic phragmacone and calcitic rostrum from the same Cylindroteuthis belemnites, along with other aragonitic benthos, from the Callovian-aged Christian Malford Lagerstätte, U.K. Our new clumped isotope data suggest that the water-calcite 18O-fractionation factor in belemnite calcite was larger than that of the commonly used δ18O thermometry equations (e.g. Kim and O’Neil, 1997), and which is currently observed in other marine calcifiers. Our reconstructions suggest that the oxygen isotope fractionation is compatible with that observed in slow-forming abiotic calcites (e.g. Coplen, 2007) and in rapidly precipitating Travertines (Kele et al. 2015). The application of more established δ18O thermometry equations (Kim and O’Neil, 1997) to belemnite calcite for temperature reconstructions has resulted in a consistent underestimation of belemnite calcification temperatures, which has led to erroneous conclusions about belemnite life habits, and underestimation of global temperatures during these greenhouse times. We therefore advocate the use of calcite equations based on low precipitation rate experiments (e.g. Coplen, 2007; Kele et al., 2015) for belemnite rostra temperature reconstructions.

How to cite: Vickers, M., Bernasconi, S., Ullmann, C., Hesselbo, S., Price, G., and Korte, C.: Belemnites, clumped isotopes and oxygen fractionation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-260,, 2019


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