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SPEED DATING! ADVICE ON SAMPLING AND APPLICATIONS FOR LUMINESCENCE DATING
TAMMY RITTENOUR, MICHELLE NELSON, and CARLIE IDEKER (UTAH STATE UNIVERSITY, LOGAN)
SHANNON MAHAN and HARRISON GRAY (USGS, DENVER)
Citation: Source: USU Luminescence LabRittenour, T., Nelson, M., Ideker, C., Mahan, S., Gray, H. (2017). SPEED DATING! Advice on sampling and applications for Luminescence dating [PowerPoint slides] (Oct. 24, 2017). Retrieved from http://www.usu.edu/geo/luminlab/luminPP.pdf
Presented at Pardee keynote Symposium P4: Speed Dating! on October 24, 2017 in Seattle, WA at the annual Geological Society of American meeting.
THERE IS A HIGH DEMAND FOR DATES!• Recent technological advances at the turn of the century
have greatly expanded archaeological and geological applications
• Users/non-specialists require a basic understanding of how and where to apply luminescence dating to optimize geochronology—we are here to help!
• Wide-spread cooperation between the luminescence labs should continue and deepen through archiving and synthesizing meta-data
• More precise, faster, and detailed luminescence dating should be driven within the luminescence community for all to benefit (i.e. share resources)
• Luminescence will become more field driven instead of lab driven
• There is no one path to truth-Illuminati’s Maxim
Nelson et al., 2015
SOME IMPORTANT ASPECTS…….
Luminescence Age (ka) = , , ⁄
• DE - Amount of stored luminescence in the mineral since last exposure to light or heat, measured in the dark lab.
• DR - Rate at which luminescence accumulates, and is proportional to the flux of radiation from radioelemental decay of K, U, Th, and Rb, in addition to cosmogenic nuclide radiation. This is the “time” part of the equation.
Natural 50ß
Time (s)35302520151050
OSL
(cts
per
0.1
6 s)
450
400
350
300
250
200
150
100
50
0
Natural 50ß
Time (s)35302520151050
OSL
(cts
per
0.1
6 s)
450
400
350
300
250
200
150
100
50
0
Dose (s)200180160140120100806040200
Lx/T
x
4
3.5
3
2.5
2
1.5
1
0.5
0
Dose (s)200180160140120100806040200
Lx/T
x
4
3.5
3
2.5
2
1.5
1
0.5
0
WHAT WE CAN (AND CAN NOT) DATE
YES!
• alluvium
• colluvium
• eolian
• fluvial
• glacial
• marine
• lacustrine
• wildfire
• biological and
anthropogenic
sediment
• rock surfaces
NO!• Clays (unless pottery for TL)• Rocks or sediment >300ka ->1Ma• Anything that fluoresces (i.e. calcite)• Anything that has internal high radiation (i.e.
zircons, apatite)
MAYBE!
• gypsum
• plagioclase
• rock glaciers
• worked rock
• fulgurites
• cave sediments
• ceramics
• fire-cracked rock
• soils
• volcanic ashes
• tsunami sediment
*These lists are not complete*
PRIMARY CONSIDERATIONS AT THE OUTCROP• Mineralogical and grain size composition
• Geologic source of sediments
• Within the datable range
• Signal resetting/likelihood of partial bleaching
• Mixing of sediment following deposition
• Burial depth and changes through time
• Homogeneity of the dose rate environment
• Water content changes thru time
• Plan for deposits that lack sand lenses (bulk sampling at night)
• Maximum temperature and length of time heated materials reached
• The importance of the question it will answer
PLEASE COME BY THE LUMINESCENCE BOOTH WITH YOUR QUESTIONS!!
Tammy and Michelle
Harrison
Carlie
Shannon
(used with permission, schematic from Dave Mallinson-East Carolina University)
"Semiconductor band structure (lots of bands 2)" by File:Semiconductor band structure (lots of bands).png: Tim Starlingvectorisation: Mliu92 - file:Semiconductor
band structure (lots of bands).png. Licensed under CC BY-SA 4.0 via Commons -https://commons.wikimedia.org/wiki/File:Semiconductor_band_structure_(lots_of_ba
nds_2).svg#/media/File:Semiconductor_band_structure_(lots_of_bands_2).svg
The Luminescence Age Equation:Age = DE (Gy)/DR (Gy/ka)
The Luminescence Age Equation:Age = DE (Gy)/DR (Gy/ka)
DE is calculated in Grays (or how much
luminescence does the mineral ALREADY
contain). It is commonly known as the Equivalent
Dose.
DR is measured Gray/kaand is commonly known
as the Dose Rate. Calculated from elemental analyses of K, U, Th, Rb
and cosmic ray components (or how fast this combination creates
luminescence in the mineral).
radiocarbon
archaeomagnetism
amino acid racemization
100 1 million100,00010,0001000
electron spin resonance
Age (years)
luminescence
fission tracks
Surface exposure dating Al & Be
magnetic polarity
210lead and uranium series
argon - argon
dendrochronologyModified from Aitken, 1998
radiocarbon
Frequently Asked Questions1. How can OSL and IRSL dates be made more precise?2. What are best practices for field sampling?3. How can the age range be extended?4. What materials can be dated reliably with OSL?5. How can we better utilize OSL meta-data for
analyses?6. What is the limit for in-situ dating development?7. When will OSL labs get dates to us faster?
Sampling Procedures
The material associated with a construction period or geological landform is
directly dated.
TL and OSL employ a variety of techniques,
each with special abilities.
There are a wide and ever growing variety of objects and landforms that can be
dated.
Conceptually the measurement of TL and OSL is simple. It needs a
light detection source such a PMT and a stimulation source that provides light
or heat.
Luminescence dating spans a wide and unique
age range
Why is OSL Dating so popular?
Quartz K-Feldspar
Advantage Disadvantage Advantage DisadvantageHighly resistant to weathering
Relatively low luminescence intensity; some quartz samples do not emit measurable luminescence
Luminescence saturates at a higher radiation dose than does that from quartz
Weathers more readily from the environment than does quartz
Luminescence signal bleaches more rapidly in sunlight than that from feldspar
Luminescence saturated at lower radiation doses compared to that emitted from feldspar
Luminescence intensity may be orders of magnitude higher than that emitted from quartz
Suffers from anomalous fading and each sample must be tested and corrected for this
Does not appear to suffer from anomalous fading
Thermal transfer can be higher in quartz than in feldspar
IRSL can be stimulated preferentially in quartz-feldspar mixtures
Difficult or impossible to correct for sensitivity change in regenerative dose data when using SAR
Can produce large and consistent data sets
Sensitivity of quartz grains due totemperature of crystallization andnumber of cycles of erosion
(From Lian, Encyclopedia of Quaternary Science, 2007)
Problems with Quartz and K-sparProblems with Quartz and K-spar
New minerals that can be usedNew minerals that can be used
Diamond and Related Materials 01/2011; 20 (8):1095-1102. DOI:10.1016/j.diamond.2011.06.012
Use of Minerals other than Quartz and Feldspars for Luminescence Dating, David Strebler, Wolfson College University of Oxford, Preset essay submitted for the degree of M.St. in archaeological science, 2013
Zircon Errors remain large due to saturation and linearity problems
Calcium Carbonate Includes large spurious signals
Halite Sample preparation is intensive and preheats must be low
Gypsum Bleaching and preheat must be low
Apatite Has extreme fading and requires >500C to drain traps
Na-Feldspar Has extreme fading and requires >500C to drain traps
Diamonds Pre-irradiation with high energy(1-2 MeV electron beam) is an essential pre-requisite for reproducible OSL-mainly radiation dosimetry
Stimulation WavelengthsStimulation WavelengthsUltraviolet 300-380 nanometers (detection quartz)Violet 380-424 nmBlue 424-486 nm (stimulation quartz) (detection feldspars)Blue-green 486-517 nmGreen 517-527 nmYellow-green 527-575 nmYellow 575-585 nmOrange 585-647 nmRed 647-780 nmInfrared 780-1130 nm (stimulation k-spar)
Measurement of luminescence
From Lian, 2007
Protocol for quartz OSL-SAR Analyses
Protocol for quartz OSL-SAR Analyses
Ways to obtain equivalent dose measurements-laser on single grain
Ways to obtain equivalent dose measurements-laser on single grain
Time (s)0.80.60.40.20
OSL
(cts
per
0.0
2 s)
50454035302520151050
Time (s)0.80.60.40.20
OSL
(cts
per
0.0
2 s)
200
150
100
50
0
Time (s)0.80.60.40.20
OSL
(cts
per
0.0
2 s)
181614121086420
Time (s)0.80.60.40.20
OSL
(cts
per
0.0
2 s)
6
5
4
3
2
1
0
New techniques in use for DEmeasurements-continuous wave
New techniques in use for DEmeasurements-continuous wave
Record: 277
Time (s)4035302520151050
OSL
(cts
per
0.1
6 s)
10,0009,0008,0007,0006,0005,0004,0003,0002,0001,000
0
Dose (Gy)242220181614121086420
Lx/T
x
2.22
1.81.61.41.2
10.80.60.40.2
0
Used when quartz (or desired mineral) has a “fast” component
Ways to obtain equivalent dose measurements-linear modulationWays to obtain equivalent dose
measurements-linear modulation
Time (s)9080706050403020100
Ram
ped
OSL
(cts
per
1.0
0 s) 16,000,000
14,000,00012,000,00010,000,0008,000,0006,000,0004,000,0002,000,000
0
Used when quartz (or desired mineral) has components that can’t be separated
Ways to obtain equivalent dose measurements-pulsed OSL
Ways to obtain equivalent dose measurements-pulsed OSL
ON‐time
OFF‐time
Used when quartz (or desired mineral) has impurities that can’t be removed
Luminescence Precision and Accuracy
Luminescence Precision and Accuracy
(Used with permission from Bull, W. Tectonic Geomorphology of Mountains Figure 6.1 p. 211).
Accuracy is the degree of truthfulness while precision is the
degree of reproducibility.
Repeated measurements are compared to arrows that are shot at a
target. Accuracy describes the closeness of arrows to the bulls eye at the target center. Arrows that strike closer to the bulls eye are considered more accurate. The closer a system's measurements to the accepted value,
the more accurate the system is considered to be.
To continue the analogy, if a large number of arrows are shot, precision would be the size of the arrow cluster.
Age limits and “practical terms”Age limits and “practical terms”Lower limit determined by
detection sensitivity and dose rate data
Upper limit is dependent on source geology (high K, U, and Th means saturation is
reached sooner) and stability characteristics of the
sample
(Thanks to David Sanderson, LED11 for permission to use his concept)
Some sources of error that are difficult to avoid include conversion from concentration data to dose rate (estimated at ~3%), absolute calibration of concentration measurements (~3%), beta source calibration (~2%), and beta attenuation factor (~2%). These estimated values are of course approximate, but it should be clear that it is difficult to obtain a luminescence age with an overall or combined standard uncertainty of much less than 5%.
Determination of Equivalent Dose-Radial plots of analyses
Radial plots allow plotting of each data point with its associated precision; any radius passing
through the origin represents a line of constant dose, and the precision of the measurement increases from
left to right.
Dose (Gy)76543210
Prob
. Den
sity
Models for DE distributionsModels for DE distributionsModel: Used for: Abused for:
Common Age(1 parameter)
Most straightforward; well bleached, not post-depositionally
mixed
If positively skewed, gives poor estimate
Central Age Large dispersions where the measured De is not consistent within error of measurements~25% overdispersion parameter
Everything to do with trying to reduce error
Minimum Age(4 and 3 parameters)
Fluvial or alluvial deposits, true values for De are drawn from a truncated normal distribution
Skewing and kurtosis
Maximum Age Grains fully bleached at deposition and then mixed with younger intrusive grains
Limited applications
Finite mixture When the sample contains several discrete grain populations (bioturbation and bleached and partial bleach)
Generally not to be applied to multi-grainaliquots
Quaternary Geochronology 11 (2012) 1-27
The promise of old (>250 ka) OSL ages by using TT-OSL
The promise of old (>250 ka) OSL ages by using TT-OSL
Quaternary Research 79 (2013) 168-174
Comparison of “normal” SAR curves with “bleached” SAR curves. Bleach at either 10 hours
sunlight or 3 hours solar lamp or 300 seconds exposure to blue diodes. The thermal transfer of
charge in quartz at room temperature was originally described by Aitken and Smith (1988). They noted that a recuperated signal (i.e. a new signal observed
after first measurement, preheating and then a subsequent stimulation) was present in many
samples and a mechanism of ‘double transfer’ was proposed, involving charge movement from the OSL 325 °C trap to a thermally shallower refuge
trap during optical stimulation, followed by retrapping in the 325 °C trap during subsequent
heating or long-term storage.
Radiation Measurements 44 (2009) 636-645
Essential Nuclides Contributing to Dose Rate (DR)
Essential Nuclides Contributing to Dose Rate (DR)
232Th238U235U & daughter products40K87RbCosmic rays (in field or standard calculation)
In silicates: penetration is 10-2 mm penetration is 100 mm penetration is 102 mm
Determination of Dose Rates (the rate of luminescence being created)
Determination of Dose Rates (the rate of luminescence being created)
Four types of environmental radiation; alpha particles, beta particles, gamma rays, and cosmic raysSources for this radiation are: U, Th, and K (naturally occurring)Cosmic rays originate from extraterrestrial sources (electromagnetic radiation)
(Picture from Duller, 2008; used with permission)
Ways to measure dose rates by obtaining elemental analyses
Ways to measure dose rates by obtaining elemental analyses
Neutron activation analysesFlame PhotometryX-ray fluorescence (XRF)Inductively-coupled plasma mass spectrometry (ICP-MS)High resolution gamma spectrometryIn-situ capsules or gamma spectrometry
Quaternary Geochronology, 2 (1–4), 2007, 117–122
The #1 problem in determining an accurate
dose rate is determining the long-term moisture content
of the sediment.The #2 problem is
determining whether there was disequilibrium in the U:Th decay chain at any point due to water flow,
sediment disintegration, or soil formation processes (i.e.
leaching of feldspars).
SummarySummaryLuminescence provides a powerful technique that compliments other dating methods or stands alone.Given the complexity of the technique, the luminescence laboratory should be consulted early in the project planning stage to provide advice and support.All models are not created equal and should not be used unless sources of errors are understood.Minerals used in luminescence dating are strongly influenced by regional geology and context.It may be possible to simply use quartz OSL components in a more efficient manner. When OSL ages are wrong, it is important to examine why they are wrong.