EGU General Assembly 2020
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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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  • CC1: Comment on EGU2020-260, Kenneth De Baets, 01 May 2020

    Thank you for this interesting work on clumped isotope in exceptionally preserved belemnites. 

    I was wondering if the (large) differences between rostrum and phragmocone values could reflect that structure specific fractionation related with differenent functional demands and/or chemistry of the internal fluids surrounding these two biogenic carbonates?  This has been suggested for cuttlefish statoliths and cuttlebones:


    • AC1: Reply to CC1, Madeleine Vickers, 01 May 2020

      Hi Kenneth - I assume you mean for the stbale isotopes? If so, then yes, we think that a) there are different equilibrium isotope fractionation factors for aragonite and calcite at any given temperature that will lead to offsets in ratios between these minerals but not in resulting temperature estimates, and b) this is complicated by the biomineralisation processes, which must be different for aragonite and and calcite, leading to different "vital effects" between the two minerals for stable isotope fractionation (but again, not affecting the clumped isotopes). 

      • CC2: Reply to AC1, Kenneth De Baets, 01 May 2020

        Yes, this was more or less what i was asking. I found the paper i previously mentioned interesting as it involves differences between different aragonitic structures within the same specimens (statoliths and cuttlebones). 

        In this context, it is also interesting that the belemnite rostrum seems to have a more similar signature to inorganic calcite than biogenic calcite in your study or did i misunderstand this?

        • AC2: Reply to CC2, Madeleine Vickers, 01 May 2020

          Yes, this is what we are noticing, that the belemnite calcite fits abiogenic, equilibrium caclite stable isotpoe equations much better than equations for molluscan calcite or rapidly+synthesized laboratory calcite (i.e. Kim and O'Neil 1997). This has also been noted in other belemnite clmped isotope studies but without having phragmacone aragonite as a test has been difficult to confirm.