Disequilibrium clumped isotope values in glendonites support formation linked to rapid CO2 degassing and methane seepage

Glendonites are calcite pseudomorphs, that form after the mineral ikaite. Their occurrence in sediments is typically seen as an indication of cold environmental conditions, even when found in predetermined greenhouse climates (Zhou et al., 2015). However, there is still uncertainty about the exact conditions that control glendonite formation and their occurrences are often in conflict with other temperature proxies (Price et al., 2013). Some authors have postulated that the temperature stability range of ikaite could be extended under certain chemical boundary conditions (Teichert and Luppold, 2013). One process that could possibly lead to such circumstances is methane seepage. Here we use clumped isotope thermometry to determine the formation temperature of glendonites. The analysed specimen, comes from a mud volcano, within the upper Paleocene, Basilika Formation near Sveagruva in Svalbard.

Thin section analyses and micro-X-ray fluorescence mapping of a glendonite specimen, show that the mineral is highly heterogeneous in terms of trace elemental incorporation. We sampled two distinct phases, for isotope analysis. The clumped isotope composition for both phases are relatively low, indicating apparent formation temperatures >50 degrees, which  are unrealistic values for the formation temperature of ikaite. The high Sulfur concentrations, surrounding sediments and low δ¹³C values of the glendonite are consistent with a formation and decomposition of the ikaite/glendonite caused by the activity of a methane seep. Degassing of CO₂ coupled to the methane seepage may have caused isotopic disequilibrium resulting in low clumped isotope values (Bajnai et al., 2020).

Sources

Bajnai, D., et al., 2020.: ‘Dual clumped isotope thermometry resolves kinetic biases in carbonate formation temperatures’, Nat Commun, 11, 4005, https://doi.org/10.1038/s41467-020-17501-0.

Price, G., et al., 2013. Isotopic evidence for long term warmth in the Mesozoic. Sci. Rep. 3 https://doi.org/10.1038/srep01438.

Teichert, B. M. A., et al., 2013. ‘Glendonites from an Early Jurassic Methane Seep — Climate or Methane Indicators?’ Palaeogeography, Palaeoclimatology, Palaeoecology, 390, 81–93. https://doi.org/10.1016/j.palaeo.2013.03.001.

Zhou, Xiaoli, e.a, 2015. ‘Ikaite Abundance Controlled by Porewater Phosphorus Level: Potential Links to Dust and Productivity’. The Journal of Geology, 123, 3, 269–81. https://doi.org/10.1086/681918.