An autochthonous glossopterid flora with latest Permian palynomorphs and its depositional setting in the Dicynodon Assemblage Zone of the southern Karoo Basin, South Africa

摘要

The discovery of a plant-fossil assemblage, situated ~70m below the vertebrate-defined Permian-Triassic boundary, allows for the characterization of part of the Late Permian landscape in the southern Karoo Basin. The megafloral and microfloral assemblages are preserved in association with an O-horizon above a weakly developed palaeosol, exposed in both New and Old Wapadsberg Pass, Eastern Cape Province, South Africa. Stable-isotope geochemical evidence indicates that pedogenesis occurred under conditions of a high regional water table, and the palaeosol was entombed by overbank or avulsion deposits in an aggradational landscape that includes tuffite. The low-diversity macroflora contains gymnospermous (Glossopteris) and sphenopsid (Phyllotheca, Trizygia) elements that include vegetative (axial, leaf) and reproductive (strobilar) remains. Glossopteris leaves are microphyllous and may reflect the taxon's physiological response to purported climate perturbation or wetland edaphic conditions, and exhibit a range of plant-animal interactions. Palynological residues contain sphenophyllalean cuticles, and the microfloral assemblage is consistent with a low-diversity glossoperid-dominated woodland with a sphenopsid understory. Extrabasinal elements include representatives of peltasperms (Alisporites), corystosperms (Falcisporites), and conifers (Lueckisporites). Pollen conforming to Lunatisporites pellucidus is present in the assemblage and is considered an indicator taxon for the latest Permian to Early Triassic. When compared to palynological assemblage zones in Australia, the Wapadsberg Pass flora is assigned a Late Changhsingian age and, therefore, represents the youngest autochthonous, Glossopteris-dominated flora to be reported from Gondwana. These results extend a palynostratigraphic framework across the Southern Hemisphere that complements other zonations presently applied to the Karoo Basin succession.