Header image: Details of a silicified fern fossil. Geoff Thompson/Queensland Museum
Andrew Rozefelds, CQUniversity Australia
The Australian continent is now geologically stable. But volcanic rocks, lava flows and a contemporary landscape dotted with extinct volcanoes show this wasn’t always the case.
Between 40 and 20 million years ago – during the Eocene to Miocene epochs – there was widespread volcano activity across eastern Australia. In places such as western Victoria and the Atherton Tablelands in Queensland, it was even more recent.
Erupting volcanoes can have devastating consequences for human settlements, as we know from Pompeii in Italy, which was buried by ash when Mount Vesuvius erupted in 79 CE. But ash falls and lava flows can also entomb entire forests, or at least many of the plants within them.
Our studies of these rare and unique plant time capsules are revealing exquisitely preserved fossil floras and new insights into Australia’s botanical history. This new work is published in the journal Gondwana Research.
The most common volcanic rocks are basalts. The rich red soils derived from them are among the most fertile in Australia.
But the rocks in which fossils occur are buried under basalts or other volcanic rock, and are called silcretes – the name indicates their origins are from silica-rich groundwaters. Silica is the major constituent of sand, and familiar to most of us as quartz.
What makes the silcrete plant fossils so fascinating is the superfine preservation of plant material. This includes fine roots and root nodules, uncurling fern fronds and their underground stems, the soft outer bark of wood, feeding traces and frass (powdery droppings) of insects, and even the delicate tissues and anatomy of fruits
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