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This is a transcript of a QuickTime movie (6.4 MB) recorded in the Pilbara in 2005. Martin Van Kranendonk, of the Geolological Survey of Western Australia, compares the geology of the Dresser formation with Yellowstone.


This is a small part of what’s known as the North Pole Dome, and the hills on my left, over in this direction, consist of rocks that are 3.49 billion years old. They’re sedimentary rocks. They were deposited by water on an ancient shoreline. And in those rocks we can see that there are ripples, and, surprisingly and beautifully, fossil stromatolites that are the age of the rock. And that unit of sedimentary rock, dips down the hill slope to the bottom of the hill where there is a small fault, that’s dropped down the rocks and that’s juxtaposed it against softer weathering rocks that fill in the valley. Those are basaltic rocks, they are easier to weather, whereas the sedimentary rocks are rich in silica and they are very resistant to weathering. So, you can see the hills that are made up of sandstone and silicified material all form this positive ridge. And then the softer basalts, the darker brown rocks, which is where Adrian is standing, they weather a little bit more easily. But in the far hills you can see that there is a really irregular pattern of dark coloured rocks, crossing in a number of lines, on the hillside, in all directions. And that’s actually a series of rocks that underlies this ancient shoreline and they’re filled by hydrothermal silica which is part of an ancient fossil hot spring environment, like Yellowstone or New Zealand. And that actually just underlies that beach and was a hydrothermal system pumping hot fluids into that arena where we get stromatolites and the shoreline living. And that’s kind of nice because you’re actually seeing a bit of an oblique cross section through part of the crust. In fact, part of an ancient volcano at 3.49, had formed a bit of a caldera, shallow caldera, which is where when the magma’s erupted, the ground falls down and the water can infill and sediment infills, and you get a nice quiet situation. And at the end of a volcanic episode is when you get all this circulation of hot fluids. That’s after the main magma’s erupted, then you still have a bit of heat from that volcanic episode, and it bubbles up the water. Yellowstone a great natural example of that, it’s a big caldera, and there’s magma underneath, it’s boiling the groundwater, and it’s coming out in these hot springs. Here, we’ve got this ancient hot spring environment, more than 3.5 billion years ago, it blows the mind. But a lot of the chemistry is similar to what we see in modern environments and the stromatolites that these experts, these world experts, are looking at convince them that they are very like modern stromatolites.




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