LATE PERMIAN FLUVIAL FACIES AND ARCHITECTURES PRESERVING AN AUTOCHTHONOUS LEAF LITTER, WAPADSBERG PASS, EASTERN CAPE PROVINCE, SOUTH AFRICA

The fossil plant record in the southern part of the Karoo Basin, South Africa, has long been considered to be of little value in biostratigraphic studies due to generally poor preservation and rare occurrences in fluvial and floodplain deposits. To date, biozonation has been based exclusively on vertebrate remains within this critical time interval. Recent investigations of well studied latest Permian sections have demonstrated the presence of parautochthonous accumulations that provide insight into the dynamics of the terrestrial system. The present study focuses on the sedimentary environments exposed within two correlative sections found to preserve autochthonous leaf litters above inceptisol and gleysol horizons along the old and new roads through Wapadsberg Pass, near Graaff Reinet.

Exposed fluvial deposits consist of four subenvironments within larger meandering channel systems. Channel deposits consist of lateral accretion barforms composed of silty sandstone or very fine sandstone overlain by siltstone drapes. Channel lag deposits are thin, fine to very fine sandstone, and overlain by thick siltstone deposits representing channel fill complexes. Several rhizoconcretionary horizons characterize each channel-fill sequence. Overbank deposits include sheet sandstones of variable grain size and sorting, as well as coarse to fine siltstone in fining upward sequences of several meter scale. Calcite-cemented concretions are common in the mudrocks near the top of most fining upward sequences. Poorly developed paleosols occur both within channel fill sequences and in overbank deposits.

One paleosol horizon with in situ Vertebraria - rooting structures of Glossopteris - is capped by a well preserved, autochthonous plant assemblage. This assemblage represents the first record of a Late Permian flora from the southern Karoo Basin with glossopterid - Lidgettonia sp., Eretmonia natalensis, Glossopteris spp., and several seed types - and sphenophyte taxa - Trizygia speciosa, Phyllotheca australis, and probable reproductive organs. Hence, it is necessary to re-evaluate both the sedimentary systems and the taphonomic factors responsible for preservation of terrestrial vegetation to change accepted views of the Late Permian in South Africa.