Organ Pipes National Park - Geological Formations

Geological Formations

The Keilor Plains, where the geomorphological and geological features of heritage value are located, is part of the greater Western Volcanic Plains which cover a large part of western Victoria and extend into south-eastern South Australia and are stated to be the third largest lava plains in the world. Thes landforms were created by the incision of the Jacksons Creek into think lava flows that erupted about 2.5 to 2.8 million years ago during the Pleistocene Period. These lavas overlie steeply dipping Silurian sedimentary rocks.

Sedimentary rock and fossils found in the park are also dated back 400 million years, an indication that the area was once a sea. The rocks seen in the park have mostly dark grey or brown colour. Graptolites are seen as fossils of sea snails, sea worms and extinct floating animals in the rocks here. About 2.5 to 2.8 million years ago giant lava flows known as a flood basalt spread across the land from surrounding volcanoes.

Rock exposures of Silurian mudstones and jointed structural features of basalt are spread at many locations in the form of Basalt cliffs, boulder screes and sedimentary escarpments. The geological features in the Park, all of volcanic origin, have been categorized under the broad heads namely, the Organ Pipes, Tessellated Pavement, Rosette Rock, Scoria cone and the Sandstone layer.