Australian Parliament House will grant a small number of people special access to its underground passages to glimpse a cavernous space known as ‘the Cathedral’, and a rare sighting of an ancient geological marvel hidden somewhere in its 300×300-metre basement.
We could all do with a bit of extra perspective but rock lovers, history buffs and political nuts will be very interested in the very old treasures hidden in the basement of parliament for national science week.
To mark National Science Week, about 60 members of the public will have the opportunity to gawk at a special rock phenomenon known as an ‘unconformity’ that lies beneath the building of parliament on August 11-12.
Rather like the cult song by Beyoncé, the star attraction of the tour is a formation – but this phenomenon is a geological one and predates the 2016 pop song by roughly 435 million years.
If you imagine layers of ancient fossilised rock sediment as a sponge cake, the unconformity is a mess.
The combination of different sediments – Black Mountain sandstone from the Silurian period and younger Camp Hill sandstone member – slanting and cutting away in uneven sequence and with different ingredients indicates something major was going on (over a period of ten million years) in the Australian ground.
Back then, in fact, it was likely to have been a sea bed, and eventually mountainous. But something in between those two events is missing in the sediment record, accounting for the unconformity.
Geoscience Australia’s Dr Steve Hill said it was rare to see an unconformity in person, least of all via a short elevator ride from the resplendent Marble Foyer of APH.
“Unconformity basically means that when sediments are laid down, they’re normally conforming to each other. They’re like a whole lot of pages in a book that are stacked up and conform to each other, kind of parallel with each other as they’re building up over time,” Hill said.
“But these don’t do that – there’s a section that is tipping this way, and these are tilted like, that these ones like that,” he added, pointing to three distinct portions of a chunk of stone a few heads taller than the average person.
Parliament House was officially opened 35 years ago but it was not until about 1995 that the existence of the geologically significant unconformity became known as a matter of general awareness.
The Capital Hill site on which APH sits was regarded by the geological community to be a place of “some really interesting rock geological relationships”, according to Hill. But much of the evidence of that history was believed to have been lost following the excavation and construction of the building.
Years later, ANU academic and geologist Wolf Mayer verified the existence of the unconformity after he was chatting to some of APH’s security staff about the special formations that can be seen when driving through the tunnels of State Circle – the road that loops around parliament. It was an extreme chance discovery and a “fundamentally critical part” of understanding the geological jigsaw puzzle of the local area.
“[The discovery was] absolutely unbelievable – this key geological relationship […] was still preserved,” Hill said.
“It’s really important in how geologists put together the pieces of the jigsaw puzzle to understand how this part of the Earth around Canberra formed, and the different rocks that are involved.”
The unconformity geology tour will give members of the public a small taste of the vast basement metropolis beneath Parliament House.
Bring a sense of wonder, warm jacket and sensible shoes (hard hats are supplied) for the tour.
Members of the public can register online to attend the six tours next month.
Places are limited with tickets priced at $76 for adults and $56 for concession card holders.
Any feedback or news tips? Here’s where to contact the relevant team.