Luminescence dating including thermoluminescence and optically stimulated luminescence is a type of dating methodology that measures the amount of light emitted from energy stored in certain rock types and derived soils to obtain an absolute date for a specific event that occurred in the past. The method is a direct dating technique , meaning that the amount of energy emitted is a direct result of the event being measured. Better still, unlike radiocarbon dating , the effect luminescence dating measures increases with time. As a result, there is no upper date limit set by the sensitivity of the method itself, although other factors may limit the method’s feasibility. To put it simply, certain minerals quartz, feldspar, and calcite , store energy from the sun at a known rate. This energy is lodged in the imperfect lattices of the mineral’s crystals. Heating these crystals such as when a pottery vessel is fired or when rocks are heated empties the stored energy, after which time the mineral begins absorbing energy again. TL dating is a matter of comparing the energy stored in a crystal to what “ought” to be there, thereby coming up with a date-of-last-heated.
Please reference: Mallinson, D. 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 Aitken , ; Botter -Jensen et al.
Radiation within sediments comes from alpha, beta, and gamma radiation emitted during the decay of U, U, Th, 40 K, and 87 Rb, and their daughter products, both within the mineral grains and in their surroundings Lian , , and from cosmic rays Figure 1. Under controlled laboratory conditions, assuming the sample was collected under light-restricted conditions, controlled exposure of the sample to photons yields a luminescence response the equivalent dose, D e , the intensity of which is a function of the dose rate within the sediment, and the length of time the sample was exposed to the background radiation.
In order to measure the age, two factors must be known; 1 the environmental dose rate, and 2 the laboratory dose of radiation that produces the same intensity of luminescence as did the environmental radiation dose the equivalent dose. Dividing the equivalent dose by the dose rate yields time.
Notable among these was the development of optically stimulated luminescence (OSL) methods (Huntley et al. ) and the improved confidence in dating.
Luminescence dating is used to identify when a sample was last exposed to daylight or extreme heat by estimating the amount of ionising radiation absorbed since burial or firing. This equation very simply expresses the calculations necessary, but it is important to be aware of the factors influencing the two values used. Heterogeneous sediments and radioactive disequilibria will increase errors on Dr, while incomplete bleaching of the sample prior to burial, anomalous fading in feldspars, and the estimation of past sediment moisture content may all also add to increased errors.
The dating of sediments using the luminescence signal generated by optical stimulation OSL offers an independent dating tool, and is used most often on the commonly occurring minerals of quartz and feldspar and, as such, has proved particularly useful in situations devoid of the organic component used in radiocarbon dating. Quartz has been used for dating to at least ka, while the deeper traps of feldspar have produced dates as old as 1 ma. The use of fine-grain dating for samples such as pottery, loess, burnt flint and lacustrine sediments, and coarse-grain dating of aeolian, fluvial and glacial sediments is regularly undertaken.
While thermoluminescence TL, the generation of a luminescence signal generated by thermal stimulation is still conducted on pottery and burnt flint samples, the bulk of luminescence dating now uses optical stimulation as this releases a signal that is far more readily zeroed than that re-set by heat. Analysis of fully bleached samples is preferred as this ensures that associated errors are kept to a minimum. Despite this, procedures exist with which to identify and take account of partially bleached grains, as may be seen in fluvial, or more likely glacial sediments, where light exposure may have been attenuated by turbid or turbulent conditions.
It is important to observe certain conventions when collecting samples in order to reduce errors as much as possible. By taking samples from well-sorted sediment structures problems with heterogeneous dose rates may be avoided, and all grains are more likely to have undergone the same depositional history.
Over the last 60 years, luminescence dating has developed into a robust chronometer for applications in earth sciences and archaeology. The technique is particularly useful for dating materials ranging in age from a few decades to around ,—, years. In this chapter, following a brief outline of the historical development of the dating method, basic principles behind the technique are discussed.
fundamentally new method of optical read-out of the trapped electron population in Soon after the discovery of OSL in quartz4, a new optical dating signal in.
Optically stimulated luminescence dating at Rose Cottage Cave. A single-grain analysis demonstrates that the testing procedure for feldspar fails to reject single aliquots containing feldspar and the overestimate of age is attributed to this. Seven additional luminescence dates for the Middle Stone Age layers combined with the 14 C chronology establish the terminal Middle Stone Age deposits at 27 years ago, while stone tool assemblages that are transitional between the Middle Stone Age and the Late Stone Age are dated to between 27 years and 20 years ago.
Although there are inconsistencies in the Middle Stone Age dates, the results suggest that the Howiesons Poort at Rose Cottage Cave dates to between 70 years and 60 years ago. Much of the rich archaeological heritage in southern Africa is older than 50 years, which is the limit of the ubiquitous 14 C dating technique. In order to make appropriate inter-site comparisons of artefactual evidence, and further to compare the trajectory of human adaptation with external factors such as changing climates, it is necessary to establish a reliable chronological framework.
Optically stimulated luminescence OSL dating has become one of the foremost techniques in establishing this framework. OSL is based on the build-up and release of radiation energy in crystalline minerals, typically quartz. The charge build-up manifests as electrons, mobilized in the quartz matrix by environmental radiation, which populate pre-existing energy minima that are called ‘traps’.
Resources home v2. Introduction Services Prices. Application Central for samples up to about Lund containing quartz. Technical Geography Laboratory All sediments contain trace minerals including uranium, thorium and potassium. Water Content Calibration Water within the soil has an attenuating effect on the ambient radiation.
most methods used for dating with quartz. Optically stimulated luminescence. (OSL). A second means of releasing the electrons stored within minerals is by.
Jain Mayank, Murray A. Optically stimulated luminescence dating: how significant is incomplete light exposure in fluvial environments? In: Quaternaire , vol. Fluvial Archives Group. Clermond-Ferrant Optically stimulated luminescence OSL dating of fluvial sediments is widely used in the interpretation of fluvial response to various allogenic forcing mechanisms during the last glacial-mterglacial cycle.
We provide here a non-specialist review highlighting some key aspects of recent development in the OSL dating technique relevant to the Quaternary fluvial community, and describe studies on dating of fluvial sediments with independent chronological control, and on recent fluvial sediment. Quaternaire, 15, , , p Obtaining chronologies for fluvial deposits is an important component in understanding the fluvial response to changes in climate, sea-level, tectonic and anthropogenic factors.
Optically stimulated luminescence OSL dating is now widely used by Quaternary scientists; it can provide ages in a range well beyond that of radiocarbon and on deposits from environments not conducive to the preservation of organic matter.
Optically Stimulated Luminescence dating
Optically Stimulated Luminescence OSL dating has emerged within the last 20 years as a key Quaternary absolute dating tool, with a wide range of terrestrial and marine applications. Optical dating techniques employ ubiquitous quartz or feldspar grains to directly date the deposition of sedimentary units. As such, the optical dating methods allow the systematic chronological evaluation of Quaternary-age sedimentary sequences.
Optically stimulated luminescence dating of a probable Native In: Rink, WJ, Thompson, JW (eds) Encyclopedia of Scientific Dating Methods.
Introduction How do we measure the OSL signal? How do we measure the radiation dose rate? Another way of dating glacial landforms is optically stimulated luminescence dating OSL. OSL is used on glacial landforms that contain sand, such as sandur or sediments in glacial streams. The OSL signal is reset by exposure to sunlight, so the signal is reset to zero while the sand is being transported such as in a glacial meltwater stream.
Once the sand grain has been buried and it is no longer exposed to sunlight, the OSL signal starts to accumulate. OSL works because all sediments have some natural radioactivity, caused by the presence of uranium, thorium and potassium isotopes in heavy minerals such as zircons. We analyse the quartz or feldspar minerals in sand deposits.
Testing Luminescence Dating Methods for Small Samples from Very Young Fluvial Deposits
Optically-Stimulated Luminescence is a late Quaternary dating technique used to date the last time quartz sediment was exposed to light. As sediment is transported by wind, water, or ice, it is exposed to sunlight and zeroed of any previous luminescence signal. Once this sediment is deposited and subsequently buried, it is removed from light and is exposed to low levels of natural radiation in the surrounding sediment.
Through geologic time, quartz minerals accumulate a luminescence signal as ionizing radiation excites electrons within parent nuclei in the crystal lattice.
Luminescence dating is a well-established method of absolute chronology that They showed that there can be sufficient light penetration for OSL dating to be.
Scientists in North America first developed thermoluminescence dating of rock minerals in the s and s, and the University of Oxford, England first developed the thermoluminescence dating of fired ceramics in the s and s. During the s and s scientists at Simon Frasier University, Canada, developed standard thermoluminescence dating procedures used to date sediments. In , they also developed optically stimulated luminescence dating techniques, which use laser light, to date sediments.
The microscopic structure of some minerals and ceramics trap nuclear radioactive energy. This energy is in constant motion within the minerals or sherds. Most of the energy escapes as heat, but sometimes this energy separates electrons from the molecules that make up the minerals or ceramics. Usually the electrons will reconnect with the molecules, but some will not.
The electrons that dont reconnect eventually encounter imperfections in the microscopic structure of the ceramics or minerals, and they become trapped by these imperfections. Over time energy in the form of more and more trapped electrons is stored in these structural imperfections. By heating the ceramic or mineral to above degrees Celcius, these trapped electrons are released, creating a flash of light called thermoluminescence. When a laser light source is used to stimulate the release of electrons, the process is called optically stimulated luminescence.
Luminescence Profile In the process of making a ceramic vessel, the soft clay vessel must be heated in a kiln to harden it. The process of firing the vessel releases the trapped electrons energy , and resets the thermoluminescence clock to zero.
Optically Stimulated Luminescence (OSL) Dating
The OSL optically stimulated luminescence dating method exploits dosimetric properties of grains of minerals naturally occurring in sediments and man-made materials. In archaeology the OSL method is used to date pottery and other heated materials e. When compared with the radiocarbon method it makes possible dating objects containing no organic matter or originating in periods for which the radiocarbon method is less accurate due to the shape or lack of the calibration curve.
This paper discusses the details of recent advances in the method and several examples of its application to material from archaeological excavations of Medieval to Palaeolithic sites. Unable to display preview.
Recent advances in OSL dating techniques for feldspar, may result in this becoming the.
Put simply, OSL dating techniques gives us an estimate of the time since mineral grains were last exposed to sunlight. Professor Jacobs used her OSL dating technique to analyse 28, individual grains of quartz from Madjebebe , which revealed groundbreaking information about the arrival of the first modern humans in Australia. Little grains moving around in the landscape are like little batteries.
Sand gets buried in the archeological site and builds up energy. Scientists go into the site and take the sample in the dark, because of course if the samples are exposed to light, the signal is reset. Samples are taken back to the lab and carefully handled in darkroom conditions. Scientists can then determine how much energy was stored in that single grain since it was last exposed to sunlight. Professor Jacobs and her team analysed 28, samples from Madjebebe, which dated the archeologically significant site at at least 65, years old.
Dating the samples was a very labour-intensive project that relied on a highly skilled team in the lab to work through various stages of preparation and measurement.