THE LATE PERMIAN STRATIGRAPHY OF THE BASAL TWEEFONTEIN SECTION, EASTERN CAPE PROVINCE, SOUTH AFRICA
The basal part of the Tweefontein section consists of fining up sequences of olive gray (5 Y 4/1) siltstone in which intervals contain carbonate-cemented concretions and burrow structures. Siltstones are well or poorly cemented, resulting in a high weathering state of the latter. A new fossil-plant assemblage dominated by Glossopteris with sphenophyllanean Trizygiawas collected at a stratigraphic height of 18 m. This assemblage is similar to that reported from Wapadsberg Pass and is in close proximity to a very thin tuffite from which no datable zircon grains were recovered. Total Organic Carbon ranges from 0.2 to 0.7%, and C:N ratios vary from 4 to 33, indicating more contribution of organic matter from algal sources.
The upper part consists of a thick fluvial sandstone characterized by very fine to fine grained, subangular to subrounded, yellow-gray lithic wacke organized into trough cross bed sets. Individual bedforms may be several meters thick and show bedding variation from trough to low angle planar beds, which may be rippled. Paleocurrent direction, derived from trough crossbed axial orientations, is to the northeast.
Comparison with previously published Tweefontein stratigraphy indicates green siltstone dominates this part of this section, a similar finding to others. Depositional environments include either poorly developed paleosols or fluvial channel-fill siltstone and sandstone, indicating the sufficient water supply, and presumably wet climate conditions, during deposition of the sequence.