Our aim with this particular Earth Cache is to take you to a beautiful 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 we also figured if you are in this part of the world that you are most likely on holidays so we wanted you to relax rather than stress about Earth Cache answers.
Today we are focusing on Sandstone, you will probably visit many waterfalls while up on the Cape, the majority of them will be Sandstone based.
Here at Isabella creek we are in the Laura basin. This basin covers an area of 18,000 km2 on land and 16,000 km2 offshore. It is composed of about 2,000 m thick deposits of Middle Jurassic to Early Cretaceous sediments. Beneath these layers are up to 10,000 m of Permian sediments of the Lakefield Basin
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. In this particular case we know the Sandstones were formed around the same time that the Eromanga Sea covered inland Australia inclusive of this part of the Cape York Peninsula.
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.
Various features in sandstone are signs of the past environment:
- Ripples can indicate the local water currents or wind directions.
- Load structures, sole marks, rip-up clasts and similar features are fossil footprints of ancient currents.
- Liesegang bands are signs of chemical action after burial of the sand.
The layers, or bedding, in sandstone are also signs of the past environment:
- Turbidite sequences point to a marine setting.
- Crossbedding (truncated, tilted sandstone layering) is a rich source of information on currents.
- Interbeds of shale or conglomerate may indicate episodes of different climate.
To log this Earth Cache we require you to wander around and look at the area, 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. We have listed some sandstone features that give geologists a window into the formation of the area, can you find any of these features and tell us what conclusion you draw from these feature(s)?
2. 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)
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: austhrutime.com, geology.about.com,
