Response of land plants to the Toarcian Oceanic Anoxic Event: Palynology of a Pliensbachian–Toarcian section from the Rodiles Formation at Lastres (Asturias, NW Spain)

During the early Toarcian (~183 million years ago), massive amounts of greenhouse gases were liberated due to volcanic activity in the Karoo-Ferrar large igneous province. One of the consequences of this volcanic activity was the Toarcian Oceanic Anoxic Event (T-OAE), which is recorded as a negative δ 13 C org excursion in sedimentary accumulations of organic matter in different deposits worldwide. This event impacted marine ecosystems, causing changes to planktonic and benthic communities and a loss of diversity in the marine realm. However, responses of terrestrial ecosystems remain uncertain. Here, a comprehensive palynological study was carried out on the Rodiles Formation, Lastres (Asturian Basin, NW Spain), aiming to describe palynological assemblages, reconstruct plant communities, detect vegetation changes, and discuss potential ecological consequences. Significant changes in the composition of terrestrial plant communities and marine plankton communities were recorded, where dinoflagellate cysts were missing through the T-OAE interval. The prevalence of Cheirolepidiaceae-dominated forests before the T-OAE suggests dry and semiarid conditions, followed by a transition to fern-dominated plant communities during the T-OAE, suggesting increased humidity or seasonality. After the T-OAE, Cheirolepidiaceae forests recovered, indicating a return to drier climates and tree-dominated communities. These findings enhance our understanding of the complex relationship between climate, environment, and terrestrial ecosystems during this event, providing the first record of the terrestrial response to the T-OAE from the Northern Iberian plate. • First palynological record of the T-OAE impact on land plants in Northern Iberia. • Cheirolepidiaceae forests declined during T-OAE, replaced by fern-dominated communities. • Post-T-OAE recovery of Cheirolepidiaceae forests indicates return to drier conditions. • Dinoflagellate cyst blackout suggests major marine ecosystem disruptions. • This work show a clear response of land plants to the T-OAE in Northern Iberia.