When these quartz or feldspar minerals are exposed to the ionising radiation emitted by the radioactive isotopes in zircons, electrons within the crystals migrate and become trapped in their crystal structure.
The number of trapped electrons depends on the total amount of radiation that the mineral has been exposed to.
Sediment transport in glacial environments is often over short distances in turbid meltwater streams, which can limit the sunlight exposure that the grains of sand receive.
If the OSL signal is not fully reset, it may result in an age overestimation.
We measure this emitted light (the luminescence) and this is the first stage towards measuring the sample age.
We then give our sand sample a range of laboratory radiation doses and measure the luminescence that each dose produces to develop a calibration curve.
The biggest challenge for OSL dating in glacial environments is partial bleaching (resetting) of the luminescence signal.
This occurs if the grains of sand are not exposed to sufficient sunlight prior to deposition within a landform such as a glacial moraine.
Recent advances in OSL dating techniques for feldspar may result in this becoming the preferred mineral for OSL dating of glacial sediments, although feldspars are often more severely affected by partial bleaching than quartz.
If we assume that the radiation dose rate of the sediment has remained constant over time, then if we measure that dose rate, we can calculate the sample age.
Hollie Wynne (Aberystwyth University) stirs OSL samples being treated with acid in the preparation lab of the Aberystwyth Luminescence Research Laboratory. We make an approximation of the number of trapped electrons by measuring the light that they emit following stimulation by light (hence the name of the technique, “Optically stimulated luminescence”).
This page was contributed by Dr Georgina King from the Aberystwyth Luminescence Research Laboratory in the Institute for Geography and Earth Sciences. OSL is used on glacial landforms that contain sand, such as sandur or sediments in glacial streams.
| Calculating Age | Challenges for OSL | Case studies of OSL dating in glacial environments | References | Comments | Another way of dating glacial landforms is optically stimulated luminescence dating (OSL).