The palynology of the Toarcian Oceanic Anoxic Event at Dormettingen, southwest Germany, with emphasis on changes in vegetational dynamics

Abstract

The Toarcian Oceanic Anoxic Event (T-OAE; ~183 Ma) represents an episode of marine anoxia that lasted for several hundred thousand years. Abiotic factors contributing to the formation of the T-OAE, such as global warming, changes in weathering intensity, or sea-level change, are associated with a marked change in carbon cycling. While these factors are well studied, detailed palynological data, including marine and terrestrial palynomorphs, is still missing. Here we present comprehensive palynological data from the sedimentologically and geochemically well constrained T-OAE section in Dormettingen (SW Germany). Palynological assemblages prior to the T-OAE reflect a mixed gymnosperm-pteridophyte vegetation on land. They also include unseparated spore tetrads and sporomorphs with darkened walls indicative of environmental stress. During the early stage of the T-OAE, gymnosperms decline and only pteridophytes are recorded in the palynological assemblages, terrestrial vegetation recovery commenced before the end of the T-OAE. Contrastingly, dinoflagellate cyst diversity declines significantly in the first stage of the T-OAE and is reduced to zero towards the end of the T-OAE. Our data shows that the terrestrial ecosystems reacted early to the abiotic disturbances reflected in carbon isotope data even before the T-OAE.