Oolites are the lithified equivalent of ooids, which are small (up to 2 mm) non-skeletal carbonatic coated grains, made of concentric layers surrounding a nucleus. They are important proxies for palaeoenvironmental reconstruction. Their origin is still debated between inorganic precipitation or biotically mediated by bacteria. The most favourable environment for their formation is warm agitated shallow water, supersaturated with respect to calcium carbonate. Ooid distribution started from the late Archean and are recorded from most time periods until present, where they are found in tropical regions (i.e. Bahamas Islands). Ooids were already intensively investigated both petrographically and sedimentologically; however, few studies concentrated on the potentiality of ooids as archives for the original chemical composition of the oceans where they formed.

Previous literature highlighted that there was an anomalous and widespread deposition of oolites immediately after several mass extinction events in the geological record. The goals of my PhD project are to describe the morphology of post-extinction ooids, interpret the geochemical signature that ooids incorporated while their carbonatic cortices were growing and to correlate it with changes in ocean chemistry in the early aftermath of mass extinctions. For this purpose, I studied samples from different palaeogeographic and palaeoenvironmental settings (Emirates and Italy), related to post-end-Permian and end-Triassic extinction events. Moreover, we also provide new insights into the end-Triassic extinction events with complete mid-Norian to Hettangian δ¹⁸O_carb and δ¹³C_carb record from a key section at Wadi Milaha (Ras Al Khaimah Emirate, United Arab Emirates). 

We used a multi-technique approach: optical microscopy, modal analysis, FE-SEM imaging and elemental mapping, stable isotope ratios and LA-ICP-MS. This approach could be applied also to recent case-studies, such as the on-going climate change due to anthropogenic activities.

This project is funded by the Crafoord Fundation, the Department of Geology at Lund University, the Royal Physiographic Society of Lund and the Austrian National Committee (Austrian Academy of Sciences).

Supervisors: Sylvain Richoz (LU), Mikael Calner (LU), Anders Scherstén (LU)

Other collaborators: Isaline Demangel (LU), Leopold Krystyn (University of Vienna, Austria),  Zsófia Kóvacs (LU and University of Graz, Austria), Gerit Gradwohl (University of Graz, Austria), Simon Lernpeiss (University of Graz, Austria), Florian Maurer (TotalEnergies, France)