Hydrothermal history

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Hydrothermal history

This is a transcript of a QuickTime movie (8.2 MB) recorded in the Pilbara in 2005. Martin Van Kranendonk, of the Geolological Survey of Western Australia, describes evidence of hydrothermal activity at the Dresser formation.


What’s nice here is that you can see this vein cutting up through the sedimentary pile. And as you walk up it, the barite curls over, and down flow from that you actually get very large domical structures in this wrinkly laminate material. And I have suggested that it’s a fossil fluid pathway, where these hydrothermal fluids erupted out onto the sea floor, and that at the locality where it was at the sea floor you’ve got stromatolite growth. And that’s been highly debated by lots of people and you “need to get eyes on the rocks”. But this is certainly one place, and again once you get up to the very top, you’ve got sediment and it’s got classic barite. So these veins again are cutting up through part of the bedded sedimentary sequence, that are partly later but partly the same time. And there are sediments that are younger, all in this compressed section of sedimentary rock. So to me that indicates that there’s an interval between the two and I like this again because it shows that as that sequence is developing, and as we saw at the previous outcrop, we’ve got multiple pulses of fluid. These are long lived systems with high pressure events, low pressure events and they just crack, seal, crack, seal. And putting that in context with what you see around you, are just all these veins. Some of the veins are absolutely horizontal, so parallel to the original bedding, and they offset vertical veins and then vertical veins cut through those. It’s really quite a long fluid history moving though here.




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