Hello all, I hope everyone is well and enjoying their research! It has been a few months since my last blog so I thought I would take the chance to update you all on the new ‘joy’ in my life, Optically Stimulated Luminescence (OSL) dating!
I am currently at the beginning of a month and a half stay at the Nordic Centre for Luminescence Research, located near the town of Roskilde in Denmark. The centre, typically named Risø is headed by the messiah of everything OSL Prof. Andrew Murray, who leads a culturally diverse team of world experts with a clear goal to take OSL to new levels. The ethos of Risø is that of learning and development, with an open-door atmosphere that promotes active collaboration and a friendly working environment. Although they do have a commercial wing that specialises in the sales of their very own TL/OSL readers, the idea of paying for dates does not fly at Risø. Instead the centre aims to welcome visitors from across the globe who are driven to promote the use of OSL in their research field, and also contribute to developing the method itself.
OSL- what is it all about?
As some will know, OSL is a method of absolute dating that allows for the dating of quartz and potassium-rich feldspars grains. The main benefits of OSL over other dating methods are: the applicability within most Quaternary landscapes (due to the relative abundance of quartz and k-feldspar grains); the wide age-range of the method that can span back to the Mid-Pleistocene (giving favourable conditions); the fact that OSL dates the time of sediment deposition not exposure; and that the method is relatively quick with typical turnaround times of roughly 1-2 months, or less if you get to the lab to do the work yourself!
Photo 1: The Risø reader room-with 20 machines this is the largest OSL facility on the planet! Note OSL works on the basis that dose signatures are reset by natural light- hence the red room!
At first, the principals of OSL appear quiet straight forward. Age is simply calculated by dividing the total energy accumulated within a grain during burial as sourced from radioactive isotopes (the equivalent dose) by the energy delivered to the grain per year, as sourced from the decay of radioactive isotopes in the surrounding soil/rock matrix (the dose rate), expressed as:
Age (years)= Equivalent Dose (De) measured in Gray (Gy)
Dose Rate (Gy/year)
Unfortunately upon reading past the first few paragraphs of any OSL related text it becomes obvious that OSL dating is not quite as simple as dividing one value by another! The world of OSL is vast and the method itself is constantly being ‘tweaked’ in order to reduce uncertainty and increase scope. I shall not delve into the intricacies of the method in this blog, but I can recommend the following reading for good background information:
- Aitken, M. J., 1985. Thermoluminescence Dating. Academic Press, London – the fundamental text for all with regard to luminescence dating.
- Buylaert, J.P., Murray, A. S., Thomsen, K. J., Jain, M., 2009. “Testing the potential of an elevated temperature IRSL signal from K-feldspar”. Radiation Measurements 44, 560-565- a brilliant guide to the principals of OSL dating using post IR-IR on feldspars.
- Buylaert, J.P., M. Jain, et al., 2012. “A robust feldspar luminescence dating method for Middle and Late Pleistocene sediments.” Boreas 41(3): 435-451- Further reading to the 2009 paper on the use of OSL in studies of long-term landscape evolution.
- Duller, G. A. T., 2008. Luminescence Dating:guidelines on using luminescence dating in archaeology. English Heritage, E. Swindon- A brilliant guide that introduces the basics of OSL in a highly accessible way for all!
Photo 2- The ever so kind Christine Thiel helps with sample etching using some particularly nasty acids!
Since the late 1990’s, OSL has been utilised in numerous studies to solve complex geomorphological challenges where temporal constraints were fundamental. For a little insight I recommend the following papers that demonstrate the multi-disciplinary application of OSL:
- Cunha, P.P., Buylaert, J.P., Murray, A.S., Andrade, C., Freitas, M.C., Fatela, F., Munhá, J.M., Martins, A.A., Sugisaki, S., 2010 “Optical dating of clastic deposits generated by an extreme marine coastal flood: the 1755 tsunami deposits in the Algarve (Portugal)”, Quaternary Geochronology 5: 329 – 335
- Roberts, R., G. Walsh, et al.,1997. “Luminescence dating of rock art and past environments using mud-wasp nests in northern Australia.” Nature 387(6634): 696-699.
- Sohbati, R., Murray, A.S., Buylaert, J.P., Ortuño, M., Cunha, P. P., Masana, E.,2012 “Luminescence dating of Pleistocene alluvial sediments affected by the Alhama de Murcia fault (eastern Betics, Spain) – a comparison between OSL, IRSL and post-IRIRSL ages”, Boreas 41, 2: 250 – 262.
- Wallinga, J., 2002. “Optically stimulated luminescence dating of fluvial deposits: a review.” Boreas 31(4): 303-322.
- Willerslev, E., E. Cappellini, et al., 2007. “Ancient Biomolecules from Deep Ice Cores Reveal a Forested Southern Greenland.” Science 317: 111-114.
Well that is all from me for now! As always if you have any questions or interest with regard to anything OSL drop me an email at firstname.lastname@example.org and I shall see if I can help!!