New Zealand geological timescale

Dr James Crampton explains that all geologists need to know the age of the rocks they work with. At GNS Science, important research continues to make the New Zealand geological timescale more precise. This includes working out the detailed evolutionary sequences of fossils and the use of radiometric dating. Deep-sea rock cores provide information not available on land.

Point of interest: In this clip, you can see James ‘preparing out’ some fossil molluscs with a small drill and an optical microscope. He is revealing the fossils within the rock so they might be better identified and studied

Transcript

DR JAMES CRAMPTON One of the important jobs we’ve done here in GNS in the last few years is working on the geological timescale. Everybody uses the geological timescale – it’s fundamental to every bit of geology, whatever you’re doing. If you hand a geologist a rock, the first question they’ll ask you is, how old is it? It’s just fundamental – you can’t do anything without knowing how old the rocks are.

And so the geological timescale is the framework which we date everything, and what we’ve been working on in GNS over the last few years and we continue to work on is refining the geological timescale, making it more and more precise, and how ever good it is, a geologist always wants to know with more precision. It’s used in all sorts of mineral exploration, it’s used in earthquake research, it’s used… every aspect of geology needs to know the age.

Timescale’s getting more refined simply because people are doing a lot more work sorting out the evolutionary sequence of the fossils in much more detail. We used to know that fairly crudely – you knew roughly that that species was there and that species was there – now we’re looking at much more detail and we’re finding new and more finely divided species. And then there’s a whole range of new radiometric dating techniques that we’re being able to apply to a greater range of rock types to date those different fossil species. So there’s the two developments going hand in hand.

Deep-sea cores are very important for the development of the geological timescale, and they’re increasingly important in New Zealand. When you want to create a geological timescale, you want to get a complete succession of the fossils and the rocks from going from as old as possible right up to as young as possible and you want a complete unbroken succession. What you find on shore in New Zealand is you might get part of this succession in one place and then you cross a faultline and so the rocks are completely different, you’ve lost your succession or it’s covered over by forest or something like that, and so you get a little bit of the story from one place and then you go to another stream 50 kilometres away and you might get another bit of the story, and somewhere else you get a bit more, so you build it up piecemeal, and all the time you’re having to relate one place to another place and back again to try and build up the complete succession.

When you go to the deep sea, you can drill one hole down through 1,000 or 2,000 metres of sediment in the sea floor and you can get the whole story in one place. And there’s other issues. For example, on land, rocks tend to be weathered and so things aren’t as well preserved as they can be. If you go into the deep sea and you drill down into the seabed, you get sometimes much better preserved fossils. So there’s many advantages to looking at deep-sea cores, and they’re becoming increasingly important.

Acknowledgement: Martin Crundwell, GNS Science Additional footage from GNS Science Deep sea coring images courtesy of IODP-USIO