Multi-Proxy Palaeothermometry (δ18O, Mg/Ca, clumped isotopes) of Mid-Cretaceous Rudist Bivalves: Deciphering Stratigraphic and Seasonal Changes in Shallow-Marine Sea-Surface Temperature

The Cretaceous period is generally considered to have been a time of warm climate, but there is an on-going dispute about the existence of cool interludes - including the short-termed installation of polar ice caps. Mid-Cretaceous shoal-water ecosystems have been proven to show characteristic response modes (e.g., microencruster-blooms) to major climatic and environmental changes related to oceanic anoxic events (OAEs), times of widespread pelagic organic matter burial. Some biotic changes predate OAE1a by few 100kyrs, an observation that is in favour of gradual and pulsed volcanic CO₂-outgassing as main trigger of this event.

We aim at reconstructing the evolution of Barremian-Aptian sea-surface temperatures (SSTs) and SST seasonalities in the prelude, during and in the aftermath of OAE1a. The outer low-Mg calcite-shell layer of rudist bivalves (e.g., Toucasia), collected at carbonate platform settings in the (sub-)tropical Tethyan realm (France, Croatia, Spain), serves both as chemostratigraphic and palaeoclimatic archive. Sclerochronological variations in isotopic (δ¹⁸O, δ¹³C, Mg/Ca, clumped isotopes) and geochemical composition (Sr, Fe, Mn, Ba, Ca/Mg) provide insights into seasonal and long-term palaeoclimatic and palaeoenvironmental changes. The outcome of this work will be of significance both for those studying the triggering factors of oceanic anoxic events and the palaeoecology of rudist bivalves.