Optical luminescence dating
Cosmogenic nuclide dating is useful for directly dating rocks on the Earth’s surface.It gives an Exposure Age: that is, how long the rock has been exposed to cosmic radiation.sand dunes, beaches, river beds, etc.) and artefacts that are up to 500,000 years old.This helps us, not only to understand how the earth’s surface responds to shifts in long- and short-term climate, but also the history of human settlement and migration.It is effective on timescales of several millions of years.It assumes that boulders have not been buried and then re-exposed at the Earth’s surface.By extracting sediment cores from the clam garden terrace and wall researchers are helping determine when clam gardens on Quadra Island were first constructed and how they were maintained through time.Optically stimulated luminescence is a method of determining the age of burial of quartz or feldspar bearing sediments based upon principles of radiation and excitation within crystal lattices, and stems from the fact that imperfections in a crystal lattice have the ability to store ionizing energy (Radiation is absorbed by the crystal lattice upon sediment burial, and over time, excites electrons causing them to migrate within the crystal and become stored in traps resulting from crystal lattice defects.
This technique, as thermoluminescence, was originally developed in the 1950s and 1960s to date fired archaeological materials, like ceramics (Aitken, 1985).
Unfortunately, glacial sediments are typically difficult to date.
Most methods rely on indirect methods of dating subglacial tills, such as dating organic remains above and below glacial sediments.
Unconsolidated sediments contain magnetic minerals, such as those on the continental shelf and slope. The remnant magnetism of the sediment is a reflection of the earth’s palaeomagnetic field at the time of deposition.
The sediments can be compared to palaeo magnetostratigraphic data, and this can be used as a proxy age determination.