SubTropical Treasure Earthcache EarthCache
Pprime (P`): Paradise Lost!
SubTropical Treasure Earthcache
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An earthcache highlights geological features of the planet we live and play on. There is no geocache container to find at this earthcache site, instead, to log this earthcache, email your answers to the owner (PLEASE DO NOT INCLUDE THEM IN YOUR LOG).
You are standing underneath Turbot street in a little spot of calm within subtropical Brisbane City. Nestled between Little Turbot st, Little Roma st and Roma st is a surprising piece of geological art that has travelled a bit in recent years.
A key feature is the state of the art water harvesting feature which captures stormwater runoff from the Turbot Street overpass which is stored on-site in rainwater tanks for use in the water feature and irrigation system.
On any particularly stressful workday you may find me, coffee in hand, communing with this piece of hidden charm. At night, or on rainy days, you may also see other transient residents - please respect their property if you are visiting this spot.
It really is a subtropical treasure. Here you will find the tree fern, elkhorn, native ginger, two palms, palm nuts fungi, king orchids and scattered leaves. Sort of. They are carved into some blocks of Sandstone.
So, what Is Sandstone? Sandstone is a sedimentary rock, which means it was deposited in a water environment, much like you see the mud flats in Moreton Bay, east of Brisbane, being deposited today. In geological terms, other types of rock are Igneous (eg. granites), Volcanics (eg. Basalts) and Metamorphics (eg. slates).
- Sedimentary rocks are formed in low temperature, low pressure environments on the surface of the earth.
- Igneous rocks are molten rocks that came up from depth, but didn't reach the surface.
- Volcanic rocks did reach the surface and usually flowed.
- Metamorphic rocks are any rocks that have been subjected to deforming temperatures and pressures.
The main constituent of all sandstone is grains of quartz. The quartz is stuck together by a natural cement of clays and traces of other minerals. So if you took a 'thin section' of sandstone and looked at it under a microscope, you would see grains of sand with a cement matrix. This sandstone is Helidon Sandstone, and is mainly 'fine' to 'medium' grained, which means the grains of sand are relatively fine and hard to see with the naked eye. It was quarried in Helidon, west of Brisbane.
When And How Was Helidon Sandstone First Deposited? Helidon Sandstone takes its name after the geological formation named after the town of Helidon in South East Queensland, Australia. A formation is a uniform rock type that was deposited at the same time and is consistent enough to recognise in different locations. Helidon Sandstone is part of the Bundumba Group, which was deposited in the Mesozoic Era. The Mesozic Era is made of three separate geological time periods called Triassic, Jurassic and Cretacious. These periods range from 240 million years ago to 65 million years ago. Helidon Sandstone was deposited in the Upper Triassic to Lower Jurassic, which makes it about 200 million years old (in a range from 210 to 190 million years). The sandstone was deposited in a fluviatile environment, which means rivers and estuaries. This was a fresh water environment. A landmark of a fluviatile deposit is 'cross bedding' and you can see examples of this in road cuttings as you travel between the towns of Helidon and Gatton and of course in the quarries at Helidon. Bedding defines how the rock was originally deposited. Helidon Sandstone was flushed with hot waters and gases and this altered the make-up of sandstone. The stone was close enough to be altered, but not so close as to be wiped out. It made the stone harder and recrystallised the quartz grains in the rock. In 'thin section' the quartz grains are tightly interlocking and this adds to the compressive strength.
Information adapted from Helidon Sandstone Industries website April 2013
Your mission today is to determine a few simple facts about this SubTropical Treasure:
Q1. How many stone blocks are there here?
Q2. What sort of stone blocks are they?
Stand with the waterfall at your back and take a look at the lone stone opposite you.
Q3. What geological (not artistic) feature strikes you immediately as you look at it?
Now step back and look at all the stones for the same sort of feature.
Q4. Given what you have learned above, describe what you think might have caused these features?
It would be great if you could also post a photo of yourself, your caching team or at least a symbol representing your caching team at this location. Please don't do so in a manner that gives away answers to these questions, but perhaps in front of the freshwater lens (?)
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