Description
Paleoclimate research into cold climates uses the geological structure called glendonites, which are calcite (CaCO3) that pseudomorphically replaced the metastable, low temperature calcium carbonate mineral ikaite (CaCO3•6H2O). Such research assumes that the chemical tracers of climatic conditions is retained during the pseudomorphic reaction, however, in several instances glendonites are found in the same stratigraphic section as warm climate indicators, such as palm trees. Therefore, this assumption has recently been brought into question.The ability of a pseudomorphic replacement reaction to retain chemical signatures is dependent on its mechanism, i.e. whether it occurs via a solid-state process or is fluid-mediated. Breakdown of the ikaite structure produces water in situ. This means that it can become self-propagating as the water produced will activate and perpetuate a fluid-mediated mechanism, in other words the ikaite can eat itself from the inside out in a cannibalistic manner. Water that is released can be isolated in pores that are also generated during the transformation reaction as there is a large volume deficit (-67%) due to the large volume differences of the calcite and ikaite molar volumes. Thus, the reaction can also produce self-contained microreactors within the original crystal.
Here I will look at vibrational spectroscopy and X-ray tomography evidence for how the pseudomorphic replacement reaction occurs. These techniques provide us with evidence for the reaction mechanism and the extent of coupling between key steps in the fluid-mediated reaction that will dictate the ability of this system to retain chemical tracers for paleoclimatic research.
| Period | Dec 2023 |
|---|---|
| Held at | GFZ German Research Centre for Geosciences, Germany |
| Degree of Recognition | Local |