Geocaching Rocks 1 Traditional Cache
Ngaambul: No response from owner. If you wish to repair/replace the cache sometime in the near future (next 30 days), just contact us (by email), and assuming it meets the current guidelines, we'll be happy to unarchive it.
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(regular)
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Being interested in Geology and rocks, I plan to progressively place geocaches around Adelaide and its surrounds reflecting the Geological history of the Adelaide Region. As more are placed, I am hoping to build up knowledge as to why the landscape here is the way it is. I find it very interesting and I hope you do too.
Chapter 1 – Marinoan Series.Go to the following co-ordinates and find the cache. You are standing on the remains of an ancient ocean that had existed here around 600 million years ago. Australia was joined to Antarctica, single–celled bacteria are just beginning to evolve to simple invertebrates and the only plant life around here is Algae. There were no land plants.As sand and other sediments are washed up from the ocean, a layer of this sediment is created. This is what is happening today at most beaches around the world (without human intervention). This hardens and more sediment is deposited on top of the previous layer and so on and so on… As this thickens, the weight and pressure cause the rock to sink down slowly and this compacts into sedimentary rock. The kind of sediment and the size of the mineral grains from this deposited material can tell us a lot about what happened here.At this spot, the sediment layers have been turned onto its side due to forces and pressure about 500-530 million years ago. What we have now is a cross-section of the deposited layers. Each individual layer you see here represents thousands of years of sediment deposited. In fact, as you walk from the ocean to the cliff, you pass over millions of years of history.Have a look at the cliff. You will see faint ripple marks facing you. Weathering and erosion have exposed this layer for all to see. This, as well as the sandy rock (Sandstone) is an indication of a shallow water environment. Walk along any sandy beach today and you will see the same ripple patterns being created. Walk towards the water and you will notice that the rock suddenly becomes very dark green / purple in colour. The grains here are very fine and they flake off (Shale). This is an indication of a deep water marine environment with water depths greater than 100 metres. So what has happened here?As you walk from the water towards the cliff, the rock sequence gets older. The rock layers at the cliff are older than the layers at the ocean. This spot has undergone some serious water level changes! It was a quiet beach, then the water level rose to between 100-500 metres and then dropped again to levels we have today.It has been found that this dark layering actually has a direct relationship with a great global ice melt and greenhouse warming around 600 million years ago. This particular characteristic and well known geological layering can be found at various places around the world and is known as the Marinoan Series, since this group of rocks were first defined here at Marino. Imagine if this event was to happen today!This is a simple small cache in an interesting area. Follow the cliff to the South about 40 metres (around the slight corner) and halfway up the cliff is an Anticline fold structure. This is a bend in the layer that looks like an upside-down u, with a slight hollow under it. This is further evidence of the forces and pressure that this area underwent. In fact, it is the same forces that helped push up the Mt Lofty and Flinders Ranges all those millions of years ago.Interesting Fact: At the time many of these sandy, shoreline sediments were deposited, Eastern Australia didn’t exist. In fact, the coast here would have been backwards with the land where the ocean is now and the ocean where the land is now at the time. The shore front existed from this spot, followed the Flinders Ranges, through the SA/QLD border and up to Cape York Peninsula, QLD (known as the ‘Tasman Line’). Go on the water towards Yorke Peninsula here and you would have been on prime real estate as this was part of the ‘Pacific Ocean’ shoreline at the time.
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