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    • Rights: University of Waikato
    Published 2 September 2016 Referencing Hub media
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    Dr Marcus Vandergoes, of GNS Science, outlines the relative and absolute dating1 methods used on a sediment core2 from Ōkārito Pākihi in Westland. AMS radiocarbon dating3 of organic4 material is shown at the Rafter Radiocarbon Dating Laboratory of GNS. OSL dating of sediments5 is shown at the Luminescence6 Dating Facility of Victoria University of Wellington.

    Transcript

    DR MARCUS VANDERGOES
    Relative dating7 is just a sequence of events. If you look at sediment8 building up over time, you know that the sediment at the bottom is going to be older than the sediment at the top, so any environmental changes that have occurred at the top of a core are younger than what has happened at the bottom of the core.

    Some of the different absolute dating9 methods are things like radiocarbon dating, but in particular AMS dating. We also use OSL dating, which is optically stimulated luminescence dating, and use the events in geological times such as volcanic eruptions that have a known age, and if we find evidence10 of those eruptions in our sediment cores11, we can use those to help us date sediment sequences as well.

    We use a number of different methods because sometimes you can only use one method at a different part of the core. Other times, we want to cross check that we have an actual age that we are relying on, so we can use different methods to compare against each other to make sure we know the age of an event that has occurred. We use AMS dating back to the last 50,000 years because that’s its age limit that it can be used in.

    The main thing for radiocarbon dating and AMS dating is that it relies on using organic matter12 to get an age from. If you’ve got a part of the core that is primarily inorganic13 matter14 – silt15, sands, clays – you have to look at a different technique and that is where we use OSL. Basically, OSL can only be used on inorganic material.

    OSL for our situation is not as precise as AMS dating for instance, primarily because when we take a sample to use, we need to take a large amount of sediment to run one of these analyses on, and the larger amount means that you actually have to take a large representative of sediment in time to do that. So it has larger errors associated with the age – that age may actually incorporate several thousands of years – whereas the AMS age may only incorporate tens to a hundred years.

    Acknowledgement:
    Dr Uwe Rieser & Ms Ningsheng Wang, Luminescence Dating Laboratory, Victoria University of Wellington
    Dr Phil Shane, University of Auckland

    1. absolute dating: Finding the actual dates of geological or archaeological objects. Normally expressed as calendar years ago.
    2. sediment core: A sample obtained by drilling into geological material using a long, hollow tube. The organic and inorganic layers provide a vertical history of geologic and climatic conditions over time.
    3. radiocarbon dating: Working out the approximate age of a very old object, such as bones or seeds, by measuring the amount of carbon 14 (C-14) it contains. When an organism dies, it no longer absorbs C-14. The C-14 it does contain in its tissues then starts to decay at a constant rate (half-life of 5,730 ± 40 years). The approximate date at which an organism died can be calculated by measuring the amount of C-14 left.
    4. organic: 1. Molecules that contain carbon and that have a biological origin. 2. Grown using natural processes with nutrients from natural sources.
    5. sediments: Material that settles to the bottom of a liquid. In geology, it describes the solid fragments of inorganic or organic material that come from the weathering of rock and are carried and deposited by wind, water or ice.
    6. luminescence: A process in which energy stored in a material is given off as light when suitably stimulated.
    7. relative dating: Putting a series of events or objects, such as rock layers, in chronological order, but does not include actual dates.
    8. sediments: Material that settles to the bottom of a liquid. In geology, it describes the solid fragments of inorganic or organic material that come from the weathering of rock and are carried and deposited by wind, water or ice.
    9. absolute dating: Finding the actual dates of geological or archaeological objects. Normally expressed as calendar years ago.
    10. evidence: Data, or information, used to prove or disprove something.
    11. sediment core: A sample obtained by drilling into geological material using a long, hollow tube. The organic and inorganic layers provide a vertical history of geologic and climatic conditions over time.
    12. organic matter: The decomposed remains of living organisms and their waste products.
    13. inorganic: Atoms and molecules that are of inanimate (non-biological) origin.
    14. matter: The basic structural component of all things that have mass and volume.
    15. silt: A granular material of a size somewhere between sand and clay. Its mineral origin is quartz and feldspar. Silt may occur as a soil or as suspended sediment in water. It may also exist at the bottom of a water body.

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    Dr Marcus Vandergoes

    Position: Paleoclimate scientist, GNS Science. Field: Paleoecology. Dr Marcus Vandergoes is a paleoecologist at GNS Science. That means that he uses the ancient remains of plants and animals to ...

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      absolute dating

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      2. Finding the actual dates of geological or archaeological objects. Normally expressed as calendar years ago.

      organic

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      3. 1. Molecules that contain carbon and that have a biological origin.

      2. Grown using natural processes with nutrients from natural sources.

      relative dating

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      4. Putting a series of events or objects, such as rock layers, in chronological order, but does not include actual dates.

      inorganic

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      5. Atoms and molecules that are of inanimate (non-biological) origin.

      sediment core

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      6. A sample obtained by drilling into geological material using a long, hollow tube. The organic and inorganic layers provide a vertical history of geologic and climatic conditions over time.

      sediments

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      7. Material that settles to the bottom of a liquid. In geology, it describes the solid fragments of inorganic or organic material that come from the weathering of rock and are carried and deposited by wind, water or ice.

      evidence

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      8. Data, or information, used to prove or disprove something.

      matter

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      9. The basic structural component of all things that have mass and volume.

      radiocarbon dating

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      10. Working out the approximate age of a very old object, such as bones or seeds, by measuring the amount of carbon 14 (C-14) it contains. When an organism dies, it no longer absorbs C-14. The C-14 it does contain in its tissues then starts to decay at a constant rate (half-life of 5,730 ± 40 years). The approximate date at which an organism died can be calculated by measuring the amount of C-14 left.

      luminescence

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      11. A process in which energy stored in a material is given off as light when suitably stimulated.

      organic matter

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      12. The decomposed remains of living organisms and their waste products.

      silt

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      13. A granular material of a size somewhere between sand and clay. Its mineral origin is quartz and feldspar. Silt may occur as a soil or as suspended sediment in water. It may also exist at the bottom of a water body.

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