Cosmogenic isotopic dating

Definition

Calculating the age of rock and sediment surfaces according to their concentration of cosmogenic isotopes.

Cosmogenic isotopes, such as ²⁶Al, ¹⁰Be, ²¹Ne, ³⁶Cl, ¹⁴C, and ³H, are produced in the atmosphere as meteoric nuclides and at the surface of the Earth as in situ terrestrial cosmogenic nuclides, or TCNs, by interaction between cosmic particles and target atoms (Gosse and Phillips, 2001; Dunai, 2010). The production of TCN depends on geographic location and altitude.

Cosmic particles are attenuated so that they produce cosmogenic isotopes only within the upper several meters of the Earth’s crust. Therefore, the concentration of TCN in rock or sediment is a good indication that it spent time close to or at the surface.

The concentration of TCN in a sample can be interpreted in two end-member ways (Bierman, 1994):

• 1. Representing a constant erosion rate (E) over a long time (t ≈ ∞)

  $$N = \frac{P}{{\lambda} + \frac{E}{\Lambda/\rho}}$$

  (1)
  ...