Understanding the origin of dolomite in the sedimentary record: the contribution of clumped isotope thermometry.

The formation of dolomite in the sediments of the Sabkha of Abu Dhabi was the subject of Judy’s PhD thesis and the question of the origin of dolomite remained at the center of her scientific interests throughout her career. The main focus was on the influence of microbial activity on dolomite formation, both in the field and through laboratory experiments. Over the years, Judy’s contributions particularly advanced our understanding of the role of microbes in the formation of dolomite.

With the development of clumped isotope geochemistry, a new tool is now available to better characterize the conditions leading to the formation of dolomite in the geological record. This tool exploits the preference of¹³C-¹⁸O bonds in carbonate molecules to form with decreasing temperature and provides a thermometer that can be used to constrain the formation temperature and the oxygen isotope composition of the fluids involved in the precipitation of dolomite. The interpretation of dolomite clumped isotopes in the geological record, however, is complicated by the fact that early-diagenetic dolomite is generally poorly ordered and non-stoichiometric, and it converts to a more stable form during diagenesis. In this contribution we will present case studies from the Alps to show how the original clumped isotope compositions of dolomite are modified during diagenesis under different thermal regimes, and we will discuss the preservation of clumped isotope signatures in dolomite.