Wilson Botanic Park is a 100 acre oasis built in an old blue metal quarry. The quarry was founded by William Wilson in 1859 when he recognised a business opportunity and began excavating the site which become renowned for producing some of the highest quality basalt in the Victoria. The Quarry ceased operation in 1976 and subsequently the land was donated to the community. It has been developed by the City of Casey with the aim of using modern relatives of the plants that grew here more than 22 million years ago. The park allows students to visit the park and study geology, palaeobotany and paleoecology.
Exploratory drilling has found extensive beds of soft mudstone, course sand and an abundance of fossils. Two fossil seams have been discovered. The first was discovered in 1902, I have noted its location on the map (Red line) but the actual seam is no longer visable. The second was dug in the late 1980’s there isn’t much to see there either other than a large hole in the ground not far from GZ.
Mudstone sandwiched between layers of Basalt have produced one of Australia’s oldest known Eucalyptus fossils. It is thought that fossils come from the Bloodwood group of Eucalypts. It is believed that the area was a temperate rainforest with backwater swamps 22 million years ago containing laurels, conifers, cycads, beeches and members of the protea family.
Basalt is one of the most common rock types in the world. It is a fine-grained hard rock that forms when lava flows from volcanoes which makes it an igneous rock. Basalt has high liquidus and solidus temperatures: values at the Earth's surface are near or above 1200 °C (liquidus) and near or below 1000 °C (solidus); these values are higher than those of other common igneous rocks. When the lava cools quickly, it turns into Basalt. Usually basalt is black or gray. Basalt is a mixture of feldspar and pyroxene, a rock made mainly of silica and oxygen.
Due to it being a very hard rock and being so common, humans have used basalt for a very long time as grinding stones for grinding grains like millet and barley. Roman engineers paved a lot of roads with basalt, and today engineers still use a lot of Basalt to make roads and railway lines.
Compared to other rocks found on Earth's surface, basalts weather relatively fast. The typically iron-rich minerals oxidise rapidly in water and air, staining the rock a brown to red colour due to iron oxide. Chemical weathering also releases readily water-soluble cat irons such as calcium, sodium and magnesium, which give basaltic areas a strong buffer capacity against acidification. Calcium released by basalts binds up CO2 from the atmosphere forming CaCO3 acting as a CO2 trap.
Carbon sequestration in basalt has been studied as a means of removing carbon dioxide, produced by human industrialization, from the atmosphere. Underwater basalt deposits, scattered in seas around the globe, have the added benefit of the water serving as a barrier to the re-release of CO2 into the atmosphere.
At GZ you will be standing with "Basalt Lake" behind you, to you left the second Fossil seam and in front of you a sheer basalt rock face.
This sheer rock face is very interesting to look at. There are three distinct layers visible to the trained eye which indicates three distinct eruptions and lava flows. Two are clearly visible the third harder to spot. Within the rocks laying around it is easy to pick up a piece of Basalt and find distinct lines like the one pictured below which suggest short periods of stop start in the flow that these rocks were formed from.
To successfully log this Earth Cache please message us the following answers: (If you would like to do a basic log to keep your stats and TB distance in order that is fine, but failure to message us the correct answers within 24 hours of such a log will result in the log being deleted.)
1. What is the main colour of the rock face and why is it this colour?
2. How many layers can you spot about how far apart are they?
3. Name at least 3 types of rocks visible at GZ
4. A photo of your team or GPSr at the Quarry (Optional)
We hope you have enjoyed your visit to WBP as much as we did.
I would like to thank 'Lex' one of the staff members at WBP for the fantastic off the cuff geology lesson he gave me on my last visit to the site to gather information for this cache. If you need to know more I have some great recourses that he copied and I can supply a copy to you or you can ask at the information desk for more information about the site.
**Wilson Botanic Park Berwick is open every day except Christmas day and Good Friday. 7.00 am – 5.00 pm 7.00 am – 8.00 pm (during daylight savings)
