Our aim with this particular Earth Cache is to take you to an interesting spot and teach you some basics, we have presented this earth science lesson on a basic level to accommodate those who avoid EC’s ‘cos they are too hard’ and also to accommodate those travelling with Children (TAWKers) who incorporate Earth caches into their curriculum.
Dog’s head rock isn’t the most scenic of places but most children get a giggle out of it and it’s literally on the side of the road on the way back from Katherine Gorge.
Today we are focusing on Sandstone which is a sedimentary rock.
The sandstone we are looking at today is remains of a larger formation that has weathered away over millions of years, it was originally connected to a larger escarpment further east where Nitmiluk National Park is, Nitmiluk National Park is the southern outlier of the Arnhem Plateau and part of the Kombolgie Formation. The Kombolgie Formation was laid down approximately 1650 million years ago and has an average thickness of around 900m.
Sandstone forms where sand is laid down and buried. Usually this happens offshore from river deltas, but desert dunes and beaches can leave sandstone beds in the geologic record too.
When sand is deeply buried, the pressure of burial and slightly higher temperatures allow minerals to dissolve or deform and become mobile. The grains become more tightly knit together, and the sediments are squeezed into a smaller volume. This is the time when cementing material moves into the sediment, carried there by fluids charged with dissolved minerals. Oxidising conditions lead to red colours from iron oxides, while reducing conditions lead to darker and greyer colours.
The sand grains in sandstone give information about the past:
- The presence of feldspar and lithic grains means that the sediment is close to the mountains where it arose.
- Detailed studies of sandstone give insight into its provenance - the kind of countryside that produced the sand.
- The degree to which the grains are rounded is a sign of how far they were transported.
- A frosted surface is generally a sign that sand was transported by wind—that in turn means a sandy desert setting.
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- Interbeds of shale or conglomerate may indicate episodes of different climate. li> •
To log this Earth Cache we require you to wander around and look at the area, (please be careful the area tends to get overgrown, both our Geo children coped at this location) consider the information given and perhaps if you need to do some research of your own, then message us with the following answers to the best of your ability;
1. What colour is the Dogs nose? Why do you think this is the case?
2. What breed of dog do you think the head belongs too?
3. Would you say the grains that make up the rock are very round? What does this suggest?
4. A photo of your team or GPS near GZ, we can't get enough of this place so upload as many photos as you like! (Optional)
5. **Bonus points to those who post a photo of their dog near GZ!
You are welcome to log your answers straight away to keep your TB's and Stats in order but please message us with your answers within 24 hours. Cachers who do not fulfil the Earth Cache requirement will have their logs deleted.
Source: Geology.com, Wikipedia.
