Cosmogenic exposure age dating

Obviously, the most common application of burial dating is the dating of cave sediments.By measuring the age of different cave levels in the walls of a river canyon, it is possible to determine the rate of canyon incision.

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So in the case of an eroding surface, the cosmogenic nuclide content can be used not to measure an exposure age, but an erosion rate ( Let us now move on to a cosmogenic radionuclide in a surface that undergoes no erosion.

Initially, the concentration of the nuclide increases almost linearly with time, but after a while, some of these nuclides are lost due to radioactive decay.

To understand this situation, it is useful to imagine one in the place of a rock particle under an eroding surface.

As the particle approaches the surface, it sees an exponentially increasing cosmic ray intensity and cosmogenic nuclide production rate.

The next line down groups all the samples that are in an erosional steady state and that, in principle have an infinite exposure age (), which effectively means an exposure age that is greater than five times the half lives of both nuclides.

Although erosion studies can be performed in bedrock, they are actually most commonly done on sediments. Consider a landscape that is in an erosional steady state and that is irradiated by cosmic rays. Above the erosion island is the ‘forbidden zone’ of physically impossible cosmogenic nuclide compositions.

When glacial striations can be observed on rock surfaces, this indicates that erosion has been negligible.

All those surfaces should plot on the zero erosion line of the banana plot.

The Earth is constantly bombarded by galactic cosmic rays, which primarily consist of protons.

Many of these electrically charged particles never reach our planet because they are deflected back into space by the Earth’s magnetic field (see Equation 3.3).

This secondary cosmic ray shower is rapidly attenuated as it travels down into the atmosphere.

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