Ingrid Urban

My Ph.D. project deals with “Geochemical characterization of oolites formed in the early aftermath of mass extinctions”. 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. 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 in respect to calcium carbonate. This is typical today for tropical regions (i.e. Bahamas Islands), but we can find oolites during the whole geological record. 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 main aims of the project is to interpret the geochemical signature that ooids incorporated while their carbonatic coating was growing and to correlate it with changes in ocean chemistry in the early aftermath of mass extinctions. For this purpose, I will study samples from different palaeogeographic and palaeoenvironmental settings (Oman, Emirates, Italy, Austria, Turkey, Iran, Sweden), related to post-end-Permian, end-Triassic, and mid and late Silurian extinction events.

Each sample will be described with thin sections and then analysed with different techniques: FE-SEM-EDX, stable isotope ratios, LA-ICP-MS for trace elements. I will compare the results with those of oolites not linked to mass extinction events. In this way, it should be possible to better understand the reasons why oolites are so widespread after mass extinctions and give further indications on factors threatening marine Life during these extreme events. 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 and the Royal Physiographic Society of Lund..

Supervisors: Sylvain Richoz, Mikael Calner, Anders Scherstén

International collaborators: Leopold Krystyn (University of Vienna, Austria), Isaline Demangel (University of Graz, Austria), Zsofia Kovacs (University of Graz, Austria)