Optically Stimulated Luminescence Fundamentals and Applications
We pioneer a technique of surface-exposure dating based upon the characteristic form of an optically stimulated luminescence (OSL) bleaching profile beneath a rock surface, which evolves as a function of depth and time. As a field test of this new method, the maximum age of Barrier Canyon Style rock art in Canyonlands. 12 Sep  We pioneer a technique of surface-exposure dating based upon the characteristic form of an optically stimulated luminescence (OSL) bleaching profile beneath a rock surface; this evolves as a function of depth and time. As a field illustration of this new method, the maximum age of a premier example of. 12 Sep Abstract.  We pioneer a technique of surface-exposure dating based upon the characteristic form of an optically stimulated luminescence (OSL) bleaching profile beneath a rock surface; this evolves as a function of depth and time. As a field illustration of this new method, the maximum age of a premier.
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Next article in issue: The influence of microstructure on deformation of olivine in the grain-boundary sliding regime. Two samples are from talus with unknown daylight exposure histories; one of these samples was exposed at the time of sampling and one was buried and no longer light exposed.
First, the OSL-depth profile of the known-age sample is modeled to estimate material-dependent and environmental parameters. These parameters are then used to fit the model to the corresponding data for the samples of unknown exposure history.
Optically Stimulated Luminescence Fundamentals and Applications
The shielded surface of the buried talus sample is decorated with rock art; this rock fell from the adjacent Great Gallery panel. Our results are the first credible estimates of exposure ages based on luminescence bleaching profiles.
The strength of this novel OSL method is its ability to establish both ongoing and prior exposure times, at decadal to millennial timescales or perhaps longer depending on the environmental dose rate even for material subsequently buried.
This has considerable potential in many archeological, geological and geo-hazard applications. In general CN dating estimates the length of time that a rock has been exposed at or near the earth's surface, while OSL dating is used to determine the time elapsed since sedimentary grains were last exposed to daylight i.
However, there is at least one other way in which luminescence signal can be used to give chronological information: While looking for a method to determine the authenticity of marble artifacts of disputed age, they investigated the daylight bleaching of the thermoluminescence TL signal with depth in several samples and proposed a model to describe the dependence of TL intensity with depth on exposure time and depth; unfortunately they were unable to quantify this exposure time reliably.
Thus daylight bleaching of the OSL signal will penetrate further into a rock surface than the corresponding TL bleaching process, and the residual surface signal will learn more here very much smaller.
Optically stimulated luminescence osl as a chronometer for surface exposure dating
These characteristics make it likely that OSL is a more suitable signal for luminescence exposure dating than TL. Here we show that OSL can be used quantitatively to estimate the exposure time of a rock surface. In luminescence measurements, this heating or optical stimulation is carried out under controlled laboratory condition so that the emitted light can be measured.
In solid rock, the latent luminescence has accumulated in response to the amount of natural ionizing radiation mainly from radioactive isotopes in the Th, U series and 40 K absorbed since rock formation. Heating or exposure to daylight, removes the latent luminescence acquired previously in a so-called bleaching or resetting process.
In a rock surface continuously exposed to daylight, this resetting will penetrate deeper into the surface with time. Using some simplifying assumptions, they presented a model of this dependence and showed it to be a good descriptor of the remaining luminescence in their naturally exposed more info. However, they were unable to determine realistic estimates of some of the parameters in the model from first principles, and they did not have any sample of known exposure history with which to calibrate their model.
Three bedrock samples of Jurassic Navajo Sandstone were collected from our study locality in Canyonlands National Park.
The temple of Apollo Delphi strengthens novel thermoluminescence dating method. JainReview of optically stimulated luminescence OSL instrumental developments for retrospective dosimetryRadiat. Monte Carlo modelling and experimental validation.
The luminescence from quartz grains extracted from this sample was measured as a function of depth from the exposed surface. The resulting luminescence profile from the known-age sample was modeled to estimate the time and spectrum-averaged product of the regional daylight flux and photoionisation cross section. The other two samples are from talus of unknown daylight exposure histories; one of these samples was exposed at the time of sampling and one was buried, and no longer light exposed.
The parameters derived using the first known-age sample are used to fit the light exposure model to the OSL-depth data for the samples of unknown exposure history.
From these fits we calculate exposure ages. The simplified form of this function is:. This assumption is discussed further in section 7. This charge had accumulated due to previous exposure to natural ionizing radiation.
Luminescence, Rock Surfaces | SpringerLink
Thus it is very likely that in most bedrock samples the radiation exposure time was sufficient for the trapped charge population to saturate. According to equation 1as the surface is exposed to light for longer periods, the latent luminescence signal is reduced farther into the rock.
This means that in a sample which has been exposed to light for a prolonged period decades to millenniathe remaining luminescence will be zero fully bleached at the surface and then increase, initially exponentially, before approaching saturation at a depth where charge detrapping due to light penetration is negligible compared to the rate of charge trapping due to the environmental dose rate [ Polikreti et al.
This depth depends on the opacity of the rock and the daylight spectrum, which is a function of the geographical coordinates, weather article source and local shadowing effects. However, several authors have shown that a few minutes [ Habermann et al. Figure 1 illustrates the evolution of such residual luminescence curves with exposure time. Profile of residual luminescence in a rock after a given exposure time, as predicted by the model.
The longer the exposure time, the farther into the rock is the luminescence signal reset. These curves are based on parameters reported for granitic rocks from Denmark by Sohbati et al. This allowed them to detect two exposure events prior to two burial periods in the history of a single cobble [ Sohbati et al. The locality is known for its narrow slot canyons formed in the Navajo Sandstone; alcoves in these learn more here contain ancient rock art.
At our site a series of preserved fluvial terraces and other geomorphic relations constrain the burial and exposure of an alcove that hosts the Great Gallery, the type locality for BCS rock art [ Jackson]. The age of the BCS rock art in the Great Gallery is controversial despite attempts to directly date it using radiocarbon [e.
The Navajo Sandstone itself is a well sorted, very fine- to fine-grained rock that is only moderately cemented with calcite, trace silica and interstitial clay. It is a feldspathic quartz arenite interpreted as having been deposited almost entirely by aeolian processes [ Sanderson; Huntoon et al. One sample HS-OSL was taken from the buried surface of a pigmented talus boulder that had previously been exposed to light Optically Stimulated Luminescence (osl) As A Chronometer For Surface Exposure Dating a part of the alcove panel.
This neighboring clast was used as a modern bleached analogue of the buried source of sample HS-OSL before it fell from the canyon wall and was shielded.
However, no information on the daylight exposure history of these samples is available. Our goal is to estimate how long the exhumed modern analogue sample has been exposed to daylight, and especially how long the buried sample with rock art had been exposed Optically Stimulated Luminescence (osl) As A Chronometer For Surface Exposure Dating light on the rock wall prior to collapse and burial.
In this latter case, by estimating its prior duration of exposure, we gain an estimate of when the rock surface first became available to the prehistoric artist. This is a valuable maximum-age constraint on the rock art. All three samples were in positions with east-facing exposure, and we assume that all were exposed to a similar light spectrum and flux.
A summary of samples is given in Table 1. For a total of 18 aliquots from all the samples described above the average IR depletion ratio was 0. We conclude click here the contribution from feldspar to our fast-component quartz OSL signal is negligible. For each aliquot, the natural OSL signal L n and the subsequent response T n to a test dose were measured in the first cycle of a single aliquot regenerative SAR protocol [ Murray and Wintle].
The test dose was kept constant for all aliquots from a given profile, but varied between 4. All the signals were dominated by the quartz fast component [ Jain et al. Nevertheless, to minimize any contribution from the more difficult to bleach and more thermally unstable medium and slow components [ Li and Li; Pawley et al. Details on the choice and testing of measurement criteria and the performance of SAR using this material can be found in Chapot et al.
In our case we do not measure dose, but nevertheless this observation serves to confirm that the test dose signal measured after the natural signal is successfully correcting for any sensitivity change that may occur in the first measurement.
Bleaching with depth model fitted to data points of three samples with different exposure histories. Each data point is an average of at least three aliquots. Error bars represent one standard error. However, Chapot et al.
See relations at Aarhus University Citationformats. Radiation Measurements29— In a rock surface continuously exposed to daylight, this resetting will penetrate deeper into the surface with time the rock 'bleaches' ; the longer the rock is exposed, the deeper this bleaching penetrates into the surface. First, the OSL-depth profile of the known-age sample is modeled to estimate material-dependent and environmental parameters. Almeidaand P.
They showed that this signal arose because of thermal transfer, and thus should be subtracted from the natural signal. Taking this into account, the residual signals were measured following Chapot et al. The measurements were carried out on multigrain aliquots, and so the measured OSL signal represents the average residual luminescence at a particular depth.
All the data points follow the general trends expected from the model compare with Figure 1. This is more clearly illustrated when the same data are presented on a logarithmic scale Figure 3. This near-surface signal has built up in the sample as a result of exposure to natural radiation during burial after the rockfall event.
Since it remains constant to a greater depth into the rock than in the exposed samples, we deduce that, before burial, the buried rock face was exposed to daylight for a longer period than the Optically Stimulated Luminescence (osl) As A Chronometer For Surface Exposure Dating exposed samples. This fitting gives a value of 6. It was Optically Stimulated Luminescence (osl) As A Chronometer For Surface Exposure Dating assumed that: To allow this, the buried data set must be modified to remove the signal acquired during burial because equation 1 forces the light signal to zero at the surface.
The results of this fitting process are shown for the road-cut sample HS-OSL and the modern analogue sample HS-OSL in Figures 2 and 3 as a dash-dot line passing through the triangles road-cut and as a dashed line through the squares modern analogue ; it can be seen that the model represents these observations well.
This fit is also shown in Figures 2 and 3as a solid line passing through the circles buried sample ; again the model provides a good representation of the observations.
The estimated exposure times, tare also derived from the fitting process: However, the exposure time they obtained from their fitting using this estimate was much shorter than what they expected for their samples.
Although the exclusion of visible light from the integration wavelength range lengthened the exposure time to some extent, it remained substantially too short. The OSL-depth curves vary significantly with the parameter values.
The experimental data measured from the known-age road-cut sample are shown as filled circles for comparison. We thus deduce that it is very likely that the attenuation characteristics of the three rock samples are indeed very similar as expected.
To calibrate this signal in terms of dose, the value of C was projected onto a typical dose-response curve from a multiple-grain aliquot of quartz to give an equivalent dose of 1. This is indistinguishable from the burial dose of 1. This means that, in principle, equation 1 estimates a minimum exposure.
Clearly it would have been desirable to have had more than one known-age sample for comparison, but nevertheless we think it is very clear that there is a chronological signal recorded in these luminescence profiles, and our quantitative analysis confirms this. The OSL method can also be used to establish exposure times for buried material, for which the cosmic ray exposure is poorly defined, and it is less sensitive to prior exposure because this can be detected in distortion of the OSL-depth profile, and modeled [ Sohbati et al.
Such a calibration can be derived from a local rock of known exposure history, as in the present study, or it may be possible to find samples where one surface was buried at the same time as the opposite surface was exposed.
It may also be possible to derive such a calibration in the laboratory using an appropriate unexposed sample and analogous bleaching conditions. Even in the absence of a calibration bleaching curve, the method can still be used to estimate relative exposure chronologies for similar rock types. As a result of the dating of the rockfall event, we know that the Great Gallery rock art must have been created sometime before 0.
This is the first time that a specific age window has been constrained for the creation of the Great Gallery rock art. We conclude that this method has considerable potential in dating many archeological and geological events such as the construction of megaliths, agricultural land clearance and enclosure, glacial advances and retreats, phases of link, and geological processes and hazards such as mass-wasting and click scarp movement.
We also thank two anonymous reviewers and the Associate Editor who helped improve this manuscript by their constructive comments. A new technique that allows researchers to determine the amount of time a rock sample has been exposed to daylight could find many applications in geology and archaeology.