00:00These spherical features that we're looking at on the shore platform are cannonball concretions.
00:07That's where they've actually formed a complete sphere,
00:10whereas most concretions are an irregular sort of shape.
00:14So these spheres probably formed as some organic matter was decomposing in the centre of the sphere,
00:24and then it's created a zone where you're getting carbonate cement and iron carbonate cement,
00:31calcium and iron carbonate cement, producing a cemented piece of rock.
00:36So the rock is exactly the same as the surrounding material,
00:39but in the concretions it's actually been cemented with calcium carbonate.
00:46It's just like concrete, for example, that's all cemented with calcium carbonate as well.
00:52And where does that calcium carbonate come from, the decomposition of the organic matter?
00:56It's come from the local environment here.
00:59Some of it may have been shells, so there could have been some shell material
01:02that's actually dissolved and then been precipitated as calcium carbonate cement,
01:07or otherwise it's just coming in from the decomposition of these volcanic rocks this is made of.
01:14So this whole sequence here is actually derived from the east from a volcanic island arc chain about 255 million
01:25years ago.
01:26And what we're looking at behind me in this point of view is looking at where the sea would have
01:33been.
01:34So we've been looking at land mass out to the east and the sea out in this direction.
01:39Obviously you'd go then back up onto the other coast of Australia as well,
01:44further over near the Bombian Caves basically.
01:49This escarpment hasn't been underwater as such.
01:53It's been uplifted when the Tasman Sea opened up about 80 million years ago.
01:59The whole escarpment got uplifted and was tilted back towards the west.
02:06That's why the rivers on the top of the escarpment all flow out to the west
02:09and join up with the Nepean River system and come out of Sydney.
02:13But what we've had is that this whole area has been uplifted during that rifting period of the opening of
02:23the Tasman Sea.
02:24How long ago did these concretions happen and how long did they take to form?
02:30That's very hard to mention.
02:33The concretions themselves would probably form over maybe a couple of thousand years.
02:41But they could have formed probably back in the Permian.
02:46In other words, within the first million years of being deposited here.
02:52But there's no way of dating them as such.
02:56Okay.
02:56So we can't actually tell exactly when they formed.
03:00250 million years ago?
03:01Yeah, 250 to 255 million years ago.
03:05And it was quickset concrete then?
03:08Yes.
03:08To get the job done in...
03:10About a thousand years to quickset.
03:12Okay.
03:12Thanks, toorah ben!
03:13Okay.
03:14Heyprit...
03:14We'll say 있� Sadly...
03:15You've young people.
03:16Until next time, you have a chociażed same criteria.
03:19Have you met!
03:19We'll be fining with any other problems...
03:19...that Bible Predator events.
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