Sprecher
Beschreibung
Eastern Australia was subjected to extensive intraplate volcanism throughout the Cenozoic and lava fields and volcanoes attest to our volcanic past. Floras buried by volcaniclastics include autochthonous elements, e.g. carbonised wood and roots in basalt flows, trees buried by ash falls and floras buried by volcanic activity. Transported leaves and branches occur as dispersed foliage in high energy ash flows (lahars) and pyroclastics or as dispersed leaves and fruits in lacustrine sediments in lakes and other depositional environments. Weathering of volcaniclastics releases silica resulting in the development of silcretes. These sub-basaltic silcretes are autochthonous assemblages consisting of palaeosols, leaf litter, ground-dwelling ferns, soil horizons and roots. The acidic (humic) and anoxic conditions provide ideal geochemical conditions for the deposition of silica and subsequent permineralization of plant remains. Soft tissue preservation of exocarps of fruits, actively growing vegetative shoots (fern croziers), bark of trees, roots and root nodules indicate burial by volcaniclastic sediments was rapid. The remarkable preservation of these plants provides the opportunity for high resolution studies of their plant anatomy. The autochthonous floras that occur in these sub-basaltic silcretes in eastern Australia are therefore discrete ‘time capsules’ of the local vegetation growing at that site at that time. These floras, however, remain little studied and represent a completely new set of data to understand the vegetation history of Australia. I will use our current work on the Melastomataceae, Casuarinaceae, Proteaceae and Pteridaceae to highlight some of the challenges in studying and interpreting these new floras.