MASS-WASTING TRIGGERED BY THE END-TRIASSIC MASS-EXTINCTION

Both the end-Permian (252 Ma) and the end-Triassic extinctions (201 Ma) likely share a common scenario that implicates massive flood basalt volcanism as the main trigger for environmental change. How volatiles (mainly CO₂ and SO₂) exerted influence on marine and terrestrial ecosystems, and whether changes in both realms proceded simultaneous, or whether ecosystem change on land cascaded into the oceans, remains poorly understood. The dieback of tree-forming vegetation during the Late Triassic Rhaetian across Europe and the proliferation of a low-growing herbaceous pioneer vegetation composed of ferns and fern allies, likely had a major impact on weathering, erosion, run-off, and depositional rates. In a recently drilled core from northern Germany (Schandelah) palynological analyses provide evidence for this scenario. In the Schandelah core, the uppermost Rhaetian Triletes Beds show increasing amounts of reworked Palaeozoic acritarchs and prasinophytes of up to 30% of the palynomorph fraction. Most of the acritarchs are singletons and can be assigned to Ordovician and Silurian species, such as Ankyrotrochus crispum, Oppilatala eoplanktonica, and Evittia spp. Further North, in the Stenlille cores from the Danish Basin, reworked Palaeozoic palynomorphs appear to constitute mainly sphaeromorphic prasinophytes. Cores from southern Germany (Mingolsheim) contain a clear sign of soil reworking, including mycorrhizal fungal remains and cysts from probable soil organisms, testifying to intense erosion that was active during the latest Triassic. These peculiar changes in palynological assemblages go hand-in-hand with important changes in sedimentology. The reworking of soil and bedrock is occurring in an interval that also contains evidence for earthquake activity in the form of widespread seismites. Moreover, XRD-analyses suggest that the latest Rhaetian contains a suite of clay minerals indicative of chemical weathering aided by humid climate conditions, such as kaolinite. All these observations may be attributed to a number of mutually non-exclusive mechanisms, including decreased plant cover, an intensified hydrological cycle due to greenhouse warming, and the doming the Central Atlantic Magmatic Province leading to continental-scale tectonic steepening of basin margins.