The palynology of the Namba Formation in the Wooltana-1 bore, Callabonna Basin (Lake Frome), South Australia, and its relevance to Miocene grasslands in central Australia

Re-examination of a sample from Wooltana-1 borehole at 242.17 m, near the base of the Namba Formation, and one from 93.5 m, near the top (not previously reported), produced pollen assemblages with rare grass pollen but abundant Milfordia homeopunctata (Restionaceae). Thus a previous interpretation of extensive grasslands during the middle Tertiary is unlikely. The algal content is significant, indicating a swamp environment. Swamp species of grasses may form a significant component of modern swamp vegetation. The family Restionaceae contains many swamp species. Other likely swamp taxa in this assemblage include Cyperaceae, Sparganiaceae and Gleichenia. Pollen of the land vegetation at the base of the Namba Formation is dominated by gymnosperms, Casuarinaceae and a little Nothofagus, thus rainforest was present. The sample near the top of the formation contains pollen of Casuarinaceae, eucalypts, Acacia, Dodonaea and Hakea/Grevillea and the vegetation was probably dry sclerophyll forest. The assemblages reported here indicate a Late Oligocene — Early Miocene age for the base of the Namba Formation (a little older than the original dating of Early — Mid Miocene) but the top is younger, most likely Late Miocene-Pliocene.