This paper aims to provide an overview concerning the optically stimulated luminescence OSL dating method and its applications for geomorphological research in France. An outline of the general physical principles of luminescence dating is given. A case study of fluvial sands from the lower terrace of the Moselle valley is then presented to describe the range of field and laboratory procedures required for successful luminescence dating. The paper also reviews the place of OSL dating in geomorphological research in France and assesses its potential for further research, by focusing on the diversity of sedimentary environments and topics to which it can be usefully applied. Hence it underlines the increasing importance of the method to geomorphological research, especially by contributing to the development of quantitative geomorphology. They are now largely used to date not only palaeontological or organic remains, but also minerals that characterise detrital clastic sedimentary material. The most common methods applied to minerals are cosmogenic radionuclides, electron spin resonance ESR and luminescence techniques. The latter were first applied to burned minerals from archaeological artefacts [thermoluminescence TL method]. Improvements of this technique led to the development, for more than twenty years, of the optical dating method [commonly referred to as Optically Stimuled Luminescence OSL ] which is now applied to sediments from various origins Wintle, The aim of this paper is to provide people involved in geomorphological research a global overview about the principles and procedures of optical dating, from the field sampling to the age interpretation.
48. OSL Dating of Sea Floor Sediments at the Okinawa Trough
The Gyrtoni Fault, defines the north-eastern boundary of the Middle-Late Quaternary Tyrnavos Basin, and was previously investigated with geological methods. Twenty five fluvial-colluvial sediment and pottery samples were collected from two paleoseismological trenches, excavated along the Gyrtoni Fault, from both the upthrown and the downthrown fault blocks.
Investigations of luminescence characteristics using various tests confirmed the suitability of the material for OSL dating using the SAR protocol. Radioactivity measurements were performed in order to estimate the annual dose rate of the surrounding soils to which the quartz grains were submitted during the burial period of the collected samples.
Julie is a Supernumerary Teaching Fellow at St John’s College, Oxford and Developing optically stimulated luminescence dating as a low-temperature.
Luminescence characteristics of quartz from Brazilian sediments and constraints for OSL dating. This study analyzes the optically stimulated luminescence OSL characteristics of quartz grains from fluvial, eolian and shallow marine sands of northeastern and southeastern Brazil, with especial focus on the applicability of the single-aliquot regenerative dose SAR dating protocol. All analyzed Brazilian sediments presented relatively high OSL sensitivity and good behavior regarding their luminescence characteristics relevant for radiation dose estimation.
While the shallow marine and eolian samples showed a narrow and reliable dose distribution, the fluvial sample had a wide dose distribution, suggesting incomplete bleaching and natural doses estimates dependent on age models. Luminescence is the light emitted by some materials, previously exposed to ionizing radiation, when stimulated by some type of activating energy Huntley The intensity of the light emitted is proportional to the dose of ionizing radiation which the material was exposed.
This relation allows several common minerals such as quartz, feldspar, zircon, and calcite to behave as a natural radiation dosimeter, i. The luminescence signal of the mineral grains is emptied naturally by sunlight during sedimentary transport. After burial, when the sediment grains are protected from sunlight, the luminescence signal builds up due to the ionizing radiation derived from nearby natural radionuclides and cosmic rays.
As a result, the luminescence signal of buried sediment grains is related to the radiation dose equivalent dose absorbed since deposition. Thus, the age of burial can be calculated through the ratio between the equivalent dose and the dose rate equation 1 :. Optically stimulated luminescence OSL dating is a method of absolute geochronology that has been widely applied in Quaternary studies since its proposition by Huntley and further development of the Single-Aliquot Regenerative Dose SAR protocol by Banerjee et al.
The SAR dating protocol is now the most frequently applied method to obtain estimates of natural radiation doses.
The principles of Luminescence 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.
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Ed Rhodes graduated in Geology from the University of Oxford University College , followed by a DPhil from the same institution studying the optical dating of quartz from sediments in Ed held a joint position as Professor of Geography at the University of Manchester , before being appointed as Professor of Physical Geography at Sheffield, starting July Palaeoseismology and fault slip-rate studies, Luminescence technical developments, Low temperature thermochronology, Grain tracing and transport rate, Palaeoclimate and palaeoenvironmental reconstruction, Fluvial and aeolian geomorphology, Grain mixing, surface processes and natural carbon sequestration.
Blair, E. Yukihara, S. In contrast, previous work has shown that the SAR procedure can be used to correct for sensitivity changes exhibited by feldspars if the cutheat is equal to the pre-heat. In this paper, a procedure that corrects for sensitivity changes in both quartz and feldspar is tested. The results indicate that for sedimentary quartz the cutheat can be equal to the pre-heat. Thus, it may be possible to develop one procedure to measure equivalent doses in a polymineral sample.
We also tested several different optical stimulation methods. Using the infrared IR -stimulated signal from a post-IR blue-stimulated optically stimulated luminescence sequence extends the potential age range when using feldpathic materials. Most users should sign in with their email address. If you originally registered with a username please use that to sign in. To purchase short term access, please sign in to your Oxford Academic account above.
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Dr Matthew Telfer
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.
Within the School of Geography and the Environment, the OLD Laboratory provides support particularly for the Landscape Dynamics research cluster, with a specific focus on low latitude environment and climate change, geoarchaeology and geomorphology. In addition our researchers continuously engage in efforts to improve and develop the methodology and to further advance our knowledge on the fundamental physical mechanisms underlying the dating method.
bThe Nordic Laboratory for Luminescence Dating, Department of Earth Sciences ments of optically stimulated luminescence (OSL) were results from Oxford.
The impetus behind this study is to understand the sedimentological dynamics of very young fluvial systems in the Amazon River catchment and relate these to land use change and modern analogue studies of tidal rhythmites in the geologic record. Many of these features have an appearance of freshly deposited pristine sand, and these observations and information from anecdotal evidence and LandSat imagery suggest an apparent decadal stability.
Signals from medium-sized aliquots 5 mm diameter exhibit very high specific luminescence sensitivity, have excellent dose recovery and recycling, essentially independent of preheat, and show minimal heat transfer even at the highest preheats. Significant recuperation is observed for samples from two of the study sites and, in these instances, either the acceptance threshold was increased or growth curves were forced through the origin; recuperation is considered most likely to be a measurement artefact given the very small size of natural signals.
Despite the use of medium-sized aliquots to ensure the recovery of very dim natural OSL signals, these results demonstrate the potential of OSL for studying very young active fluvial processes in these settings. An important facet of the development of a geochronological technique is the investigation of potential age range. Much recent work in the luminescence field has focused on maximum achievable ages using high-temperature post-infrared infrared pIRIR signals from feldspars [ 1 , 2 ].
In contrast for quartz optically stimulated luminescence OSL , the more efficient signal resetting coupled with environments where grain reworking is evident make it well suited to assessment of minimum achievable age. Notable examples are studies of young fluvial deposits [ 3 , 4 , 5 , 6 ] and dunes [ 7 , 8 , 9 , 10 , 11 ].
School of Geography and the Environment, University of Oxford
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Thus, luminescence dating provides an estimate of the time elapsed since the mineral grains were last heated or Oxford: Oxford University Press. Auclair, M.
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. A certain percent of the freed electrons become trapped in defects or holes in the crystal lattice of the quartz sand grain referred to as luminescent centers and accumulate over time Aitken, In our laboratory, these sediments are exposed to an external stimulus blue-green light and the trapped electrons are released.
The released electrons emit a photon of light upon recombination at a similar site. In order to relate the luminescence given off by the sample to an age, we first need to obtain the dose equivalent to the burial dose. Following the single-aliquot regenerative SAR method of Murray and Wintle , the dose equivalent De is calculated by first measuring the natural luminescence of a sample. Then, the bleached sample is given known laboratory doses of radiation, referred to as regenerative doses.
Luminescence dating is an absolute radiometric method of determining the age of a material since a key event in its history – typically burial in the case of sediments or firing in the case of ceramics or burnt stone. When a geological sediment is buried, the effects of the incoming solar radiation are removed. With this bleaching effect removed, the influence, albeit often weak, of naturally-occurring radioactive elements primarily potassium, uranium and thorium within the sediment together with incoming cosmic rays results in the accumulation of a signal within individual mineral grains most commonly quartz and feldspars.
It is this signal that is the key to luminescence dating techniques. Given an estimate of the rate of received ionizing radiation the dose rate, or D , and knowing the total accumulated dose the palaeodose; designated D E it is possible to derive an age since burial. This is obtained from the formula:.
In West Africa, preservation conditions of the sediments have only rarely been favorable to the recording of long sedimentary and archaeological sequences. Most of the artifacts are surface finds, making it difficult, if not impossible, to place them in chronological context, whether it be relative or absolute. However, in the Dogon Country, deep sedimentary deposits have been preserved in several sectors, trapping abundant evidence of human occupations during the Paleolithic and making it possible to study their chronology.
While the range of applicable dating methods is limited, given the exclusive preservation of mineral materials, with the exception of Holocene charcoals, conditions are favorable for dating by optically stimulated luminescence OSL : the sediments are mainly formed of quartz, which, moreover, has a particularly strong luminescence signal in this region. The radioactive elements of the uranium, thorium and potassium families are naturally present in very low amounts in all sediments.
Radioactive decay is accompanied by energy release, some of which is absorbed by nearby minerals. When these are subjected to light stimulus, the accumulated energy in the crystalline networks is released, causing a light emission: this is optically stimulated luminescence or OSL.
This site is using cookies to collect anonymous visitor statistics and enhance the user experience. Science Classification details. Abstract: Without robust age control, reconstructing the past dynamics of the Earth system in response to external forcing is problematic. Chronometry is a critical part of studying past environmenst, climates, ecology, human evolution and human landscape-use. Several excellent methods for dating ancient material exist. In many environmental contexts, however, optically-stimulated luminescence OSL dating is the only method than can be used, due to the nature of the sediments that preserve the environmental record.
Murray, P. Denby, Thermal pre-treatment in the OSL dating of quartz: is it necessary? Thermal treatment before optically stimulated luminescence OSL measurement is an important step in all widely accepted OSL dating procedures used with quartz. This is a major constraint on the design of a portable luminescence instrument for estimating ages in the field. Our results show consistency with dose estimates obtained using a standard measurement protocol including pre-heating.
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