Fig. 1 Sampling for OSL dating

Comparing the 14C and OSL dating methods

Radiocarbon (14C) has a long tradition in archaeology, for obvious reasons. The method enables dating organic matter (bones, wood, charcoal, plant remains, shells etc) back to ca. 50.000 years ago.
The more recently developed OSL dating method is complementary to 14C: it is applied to inorganic matter (such as clay, sand, bricks and pottery) and has the advantage that samples can be dated back to ca. 150.000 years ago.

Because of variations in the natural 14C concentration, the 14C method is not "absolute", and needs to be calibrated by comparing 14C dates with dates obtained from another independent (and preferably absolute) dating method. At present, this is impossible or at best problematic for samples older than ca. 25.000 14C years. Precise dating of this time range is crucial for a variety of disciplines: Palaeolithic archaeology (e.g. Neanderthal/modern human transition), palaeontology (e.g. mammoth steppe), quaternary geology (e.g. Northsea during the Glacial), and palaeo-climatology.

Fig. 2 Core of sediments with alteration of organic and non-organic layers

Comparing OSL and 14C dates for sediments will give additional information on "absolute dating" for this time range. Since the same sample cannot be dated by both methods, they can only be compared if there is an unambiguous association between them. An example is a sequence of inorganic/organic layers in a sediment (Figure 2).

CAAS will finance a pilot study comparing OSL (inorganic sediment) and 14C (plant remains) from selected sites from the Eastern Netherlands - Eerbeek, Hengelo and Ootmarsum. At present, samples have been selected; the dates will become available in 2010.

Our sequences will be considered in 3 parts:
1) younger than ca. 25.000 years
For this timerange, the 14C dates can be calibrated into absolute ages. Both 14C and OSL methods should yield the same absolute dates.
2) between 25.000 and 50.000 years
In principle 14C dating is possible, but calibration into absolute ages is problematic. Also the method becomes increasingly more sensitive for contamination close to the dating limit. OSL dating should be reliable in this timerange.
3) older than 50.000 years
This is beyond the 14C dating range: the 14C content in the samples is so small that it can no longer be distinguished from the background. So for this timerange, only dating by OSL will be  possible; results for 14C will always be >50000.