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

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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

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New techniques in use for DEmeasurements-continuous wave

New techniques in use for DEmeasurements-continuous wave

Record: 277

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10,0009,0008,0007,0006,0005,0004,0003,0002,0001,000

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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

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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.