Citation: Source: USU Luminescence Lab Rittenour, 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 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)

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) Nelson et al., 2015 • Luminescence will become more field driven instead of lab driven • There is no one path to truth-Illuminati’s Maxim SOME IMPORTANT ASPECTS…….

, Luminescence Age (ka) = 4 , ⁄ 3.5 3

2.5

2 • DE - Amount of stored luminescence in the mineral since last Lx/TxLx/Tx 1.5 exposure to light or heat, measured in the dark lab. 1 0.5

0 0 20 40 60 80 100 120 140 160 180 200 • DR - Rate at which luminescence accumulates, and is proportional Dose (s) 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. 450 Natural 400 50ß 350 300 250 200 150 OSLOSL (cts(cts per per 0.16 0.16 s)s) 100

50 0 0 5 10 15 20 25 30 35 Time (s) WHAT WE CAN (AND CAN NOT) DATE YES! MAYBE! • alluvium • gypsum • colluvium • plagioclase • eolian • rock glaciers • fluvial • worked rock • glacial • fulgurites • marine • cave sediments • lacustrine • ceramics wildfire NO! • • fire-cracked rock • Clays (unless pottery for TL) • biological and • soils • Rocks or sediment >300ka ->1Ma anthropogenic • Anything that fluoresces (i.e. calcite) • volcanic ashes sediment • Anything that has internal high radiation (i.e. • tsunami sediment zircons, apatite) • rock surfaces *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!!

Carlie Tammy and Michelle Harrison 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)

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/ka and 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). Modified from Aitken, 1998 dendrochronology

radiocarbonradiocarbon

argon - argon

210lead and uranium series

fission tracks

luminescence

electron spin resonance

amino acid racemization

Surface exposure dating Al & Be archaeomagnetism magnetic polarity

1001000 10,000 100,000 1 million Age (years) Frequently Asked Questions

1. 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 Why is OSL Dating so popular?

The material associated Conceptually the with a construction period measurement of TL and or geological landform is OSL is simple. It needs a directly dated. light detection source such a PMT and a stimulation TL and OSL employ a source that provides light variety of techniques, or heat. each with special abilities.

There are a wide and ever growing variety of objects and landforms that can be dated.

Luminescence dating spans a wide and unique age range Problems with Quartz and K-spar Quartz K-Feldspar Advantage Disadvantage Advantage Disadvantage Highly resistant to Relatively low Luminescence Weathers more readily weathering luminescence saturates at a higher from the environment than intensity; some radiation dose than does quartz quartz samples do does that from quartz not emit measurable luminescence Luminescence signal Luminescence Luminescence Suffers from anomalous bleaches more rapidly in saturated at lower intensity may be fading and each sample sunlight than that from radiation doses orders of magnitude must be tested and feldspar compared to that higher than that corrected for this emitted from feldspar emitted from quartz Does not appear to Thermal transfer can IRSL can be Difficult or impossible to suffer from anomalous be higher in quartz stimulated correct for sensitivity fading than in feldspar preferentially in change in regenerative quartz-feldspar dose data when using SAR mixtures Can produce large and Sensitivity of quartz consistent data sets grains due to temperature of crystallization and number of cycles of erosion (From Lian, Encyclopedia of Quaternary Science, 2007) New minerals that can be used

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

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

Diamond and Related Materials 01/2011; 20 (8):1095-1102. DOI:10.1016/j.diamond.2011.06.012 Stimulation Wavelengths Ultraviolet 300-380 nanometers (detection quartz) Violet 380-424 nm Blue 424-486 nm (stimulation quartz) (detection feldspars) Blue-green 486-517 nm Green 517-527 nm Yellow-green 527-575 nm Yellow 575-585 nm Orange 585-647 nm Red 647-780 nm Infrared 780-1130 nm (stimulation k-spar) Measurement of luminescence

From Lian, 2007 Protocol for quartz OSL-SAR Analyses Ways to obtain equivalent dose measurements-laser on single grain

200 50 45 150 40 35 30 100 25 20 50

15 OSL (cts per 0.02 s)

OSL (cts per 0.02 s) 10 5 0 0 0 0.2 0.4 0.6 0.8 0 0.2 0.4 0.6 0.8 Time (s) Time (s)

18 6 16 14 5 12 4 10 8 3 6 2 4 OSL (cts per 0.02 s)

2 OSL (cts per 0.02 s) 1 0 0 0.2 0.4 0.6 0.8 0 Time (s) 0 0.2 0.4 0.6 0.8 Time (s) New techniques in use for DE measurements-continuous wave

Record: 277 2.2 10,000 2 9,000 1.8 8,000 1.6 7,000 1.4 6,000 1.2

5,000 Lx/Tx 1 4,000 0.8 3,000 0.6 OSL (cts per 0.16 s) 2,000 0.4 1,000 0.2 0 0 0 5 10 15 20 25 30 35 40 0 2 4 6 8 10 12 14 16 18 20 22 24 Time (s) Dos e (Gy )

Used when quartz (or desired mineral) has a “fast” component Ways to obtain equivalent dose measurements-linear modulation

16,000,000 14,000,000 12,000,000 10,000,000 8,000,000 6,000,000 4,000,000 2,000,000 Ramped OSL (cts per 1.00 s) 0 0 10 20 30 40 50 60 70 80 90 Time (s)

Used when quartz (or desired mineral) has components that can’t be separated 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 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.

(Used with permission from Bull, W. Tectonic Geomorphology of Mountains Figure 6.1 p. 211). 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

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%.

(Thanks to David Sanderson, LED11 for permission to use his concept) 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. Prob. Density

0 1 2 3 4 5 6 7 Dose (Gy) Models for DE distributions Model: Used for: Abused for: Common Age Most straightforward; well If positively skewed, gives (1 parameter) bleached, not post-depositionally poor estimate mixed Central Age Large dispersions where the Everything to do with measured De is not consistent trying to reduce error within error of measurements ~25% overdispersion parameter

Minimum Age Fluvial or alluvial deposits, true Skewing and kurtosis (4 and 3 parameters) values for De are drawn from a truncated normal distribution

Maximum Age Grains fully bleached at Limited applications deposition and then mixed with younger intrusive grains

Finite mixture When the sample contains Generally not to be several discrete grain applied to multi-grain populations (bioturbation and aliquots bleached and partial bleach)

Quaternary Geochronology 11 (2012) 1-27 The promise of old (>250 ka) OSL ages by using TT-OSL

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.

Quaternary Research 79 (2013) 168-174 Radiation Measurements 44 (2009) 636-645 Essential Nuclides Contributing to

Dose Rate (DR) 232Th 238U 235U & daughter products 40K 87Rb Cosmic 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) Four types of environmental radiation; alpha particles, beta particles, gamma rays, and cosmic rays Sources 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 Neutron activation analyses Flame Photometry X-ray fluorescence (XRF) Inductively-coupled plasma mass spectrometry (ICP-MS) High resolution gamma spectrometry In-situ capsules or gamma spectrometry 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).

Quaternary Geochronology, 2 (1–4), 2007, 117–122 Summary Luminescence 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.