Carbon cycle perturbations during the Pliensbachian-Toarcian transition in the Monte Serrone section (Northern Apennines, Italy)

The Pliensbachian/Toarcian event (P/T-E) and the Toarcian Oceanic Anoxic Event (T-OAE) are two intervals of carbon cycle perturbations linked to massive ¹²C-enriched carbon emissions, causing severe biotic and environmental changes. Here organic carbon isotope, mineralogical composition and sedimentology have been analyzed across the Pliensbachian-Toarcian transition from the Monte Serrone section (Umbria-Marche Basin), which was deposited in a pelagic setting in the western Tethys. A marked negative carbon-isotope excursion occurred across the Pliensbachian-Toarcian boundary and lower Toarcian, respectively, which can be used to identify PTE and T-OAE in the study area. The P/T-E and T-OAE intervals witnessed carbonate production crisis revealed by reduced carbonate contents. We hold that the 0.5 m-thick laminated black shales indicated that the T-OAE was a highly condensed succession because it included the full duration of the T-OAE. Therefore, the T-OAE interval at Monte Serrone coincided not only with diminished carbonate production but also with reduced siliciclastic input, forming quite thin black shale deposition. Abundant marine organisms were present preceding the T-OAE. Nevertheless, none of them survived during the most negative carbon-isotope excursion of the T-OAE, revealing a biotic crisis at this time. Elevated seawater temperature could induce this crisis in the study area. The recovery of benthic foraminifera was delayed at Monte Serrone.