Oceanic anoxic event 3 coincided with peak Caribbean Large Igneous Province volcanism at 88 Ma

The high-volume, short-lived magma flux associated with the eruption of oceanic large igneous provinces (LIPs) is believed to have triggered Cretaceous Oceanic Anoxic Events, most notably OAE1 (~120–100 Ma) and OAE2 (~94 Ma). In contrast, OAE3 (~88–84 Ma) is considered to have occurred largely independently of LIP volcanism. Here we present a record of OAE3-related black shale deposition in Costa Rica that is coeval with the peak phase of the Caribbean LIP. Radiolarian biostratigraphy and zircon U-Pb geochronology from the Loma Chumico Formation indicate that black shale formation in the Costa Rican forearc was synchronous with the onset of OAE3 at around 88 Ma. Recently revised 40 Ar/ 39 Ar ages of LIPs show that the Caribbean LIP is the best candidate to hypothesize a causal link between OAE3 and a major magmatic event. Peak volcanism of the Caribbean LIP between 88 and 86 Ma occurred at the same time as global carbon cycle perturbations in marine and terrestrial settings, as well as oceanic anoxia. New mercury records, calibrated with carbon isotopes and used as a proxy for LIP volcanism, from ODP Hole 700B and IODP Hole U1513A suggest that the Caribbean LIP not only coincided with OAE3 but may have actually triggered it. Overall, these new and existing data suggest a significant role of the Caribbean LIP in driving environmental and climatic perturbations during the Coniacian–Santonian. • Combined stratigraphic, geochronological, and geochemical data suggest a causal link between Caribbean LIP magmatism and OAE3. • Mercury spikes from Holes 700B and U1513A, calibrated with carbon isotope data, suggest LIP volcanism shortly before and during OAE3. • Black shales from the Loma Chumico Formation (Costa Rica) date to 88–87 Ma. • Black shale deposition matches the onset of OAE3 and peak volcanism of the Caribbean LIP.