Six disused quarries tell of a much earlier Canberra geoheritage story

Dr Douglas Finlayson

In the central part of Canberra there are six disused quarries that illustrate various aspects of the Silurian tectonic setting of the eastern Lachlan Origin. These quarries were developed for engineering and construction purposes during the building of the nation’s capital city. They are located around Black Mountain, Mount Ainslie, Red Hill, Mount Mugga Mugga, Yarralumla brickworks and Acton Peninsula.

Among this group of central Canberra quarries the outcrops can demonstrate a shallow marine environment about 438-433 Ma, dacitic ignimbrite volcanism at 428-424 Ma, a second eruptive history about 424-422 Ma, limestone deposition in a warm shallow marine environment near the equator at 428-425 Ma, Silurian fossils in a tuffaceous sandstone, siltstone, mudstone marine environment at 424-423 Ma, and later metamorphism by a northern pluton of the Bega Batholith about 417 Ma.

Together these quarry rock outcrops backup paleogeographic reconstructions that indicate that during the early part of the Paleozoic era Australia was part of the Gondwana supercontinent and largely surrounded by warm waters north of the Equator. The Paleo-Pacific Ocean lithospheric plate was colliding with Gondwana and there were subduction zones, with associated island arc volcanoes and earthquakes, dipping under its embryonic Australian margins.


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