Oceanic anoxia developed during the latest Ordovician glacial pulse around 444 million years ago, concomitant with the Late Ordovician Mass Extinction, and lasted for several million years into the early Silurian, as testified by geochemical proxy records and large-scale organic-rich marine black shale deposition. Yet, the mechanisms responsible for this protracted period of oceanic deoxygenation and organic carbon burial, which was an order of magnitude longer than the ocean anoxic events of the Mesozoic, as well as its coupling with the evolution of Earth's habitability and the marine biosphere, remain poorly documented. This session intends to improve our understanding of the triggers, characteristics and consequences of oceanic anoxia around the Katian–Rhuddanian boundary. We welcome contributions using sedimentology, paleontology, geochemistry, and Earth system modeling to address these questions. We especially encourage submissions providing new and innovative insights regarding the mechanisms, feedbacks, or quantitative thresholds of black shale deposition at that time.