Name: isolation of quartz grains for optically stimulated luminescence (osl) dating of quaternary sediments for paleoenvironmental research
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Description: Watch this Scientific Journal Video about Isolation of Quartz Grains for Optically Stimulated Luminescence OSL Dating of Quaternary Sediments for Paleoenvironmental Research at JoVE.com

Support of the Geoluminescence Dating Research Laboratory has been provided by Baylor University and grants from the National Science Foundation (GSS-166023), National Geographic (#9990-1), and Atlas Sand. Discovery and learning in this lab were enhanced by our many collaborators, students, and visitors that have brought new perspectives, ideas, and approaches.

<ol>
	<li>Murray, A. S., Wintle, A. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+single+aliquot+regenerative+dose+protocol:+Potential+for+improvements+in+reliability.">The single aliquot regenerative dose protocol: Potential for improvements in reliability.</a> Radiation Measurements. 37 (4-5), 377-381 (2003).</li><li>Wintle, A. G., Murray, A. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+review+of+quartz+optically+stimulated+luminescence+characteristics+and+their+relevance+in+single-aliquot+regeneration+dating+protocols.">A review of quartz optically stimulated luminescence characteristics and their relevance in single-aliquot regeneration dating protocols.</a> Radiation Measurements. 41, 369-391 (2006).</li><li>. RISO Luminescence Analyst, Version 4.57 Available from: <a target="_blank" href="https://users.aber.ac.uk/ggd">https://users.aber.ac.uk/ggd</a> (2021)</li><li>Aitken, M. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> An introduction to optical dating: the dating of Quaternary sediments by the use of photon-stimulated luminescence. , (1998).</li><li>Duller, G. A. T., Wintle, A. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+review+of+the+thermally+transferred+optically+stimulated+luminescence+signal+from+quartz+for+dating+sediments.">A review of the thermally transferred optically stimulated luminescence signal from quartz for dating sediments.</a> Quaternary Geochronology. 7 (1), 6-20 (2012).</li><li>Brown, N. D., Forman, S. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Evaluating+a+SAR+TT-OSL+protocol+for+dating+fine-grained+quartz+within+Late+Pleistocene+loess+deposits+in+the+Missouri+and+Mississippi+river+valleys,+United+States.">Evaluating a SAR TT-OSL protocol for dating fine-grained quartz within Late Pleistocene loess deposits in the Missouri and Mississippi river valleys, United States.</a> Quaternary Geochronology. 12, 87-97 (2012).</li><li>Forman, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Luminescence+Dating+in+Paleoseismology.">Luminescence Dating in Paleoseismology.</a> Encyclopedia of Earthquake Engineering. , 1371-1378 (2015).</li><li>Lepper, K., McKeever, S. W. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=An+objective+methodology+for+dose+distribution+analysis.">An objective methodology for dose distribution analysis.</a> Radiation Protection Dosimetry. 101 (1-4), 349-352 (2002).</li><li>Tsukamoto, S., Duller, G. A. T., Wintle, A. G., Muhs, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Assessing+the+potential+for+luminescence+dating+of+basalts.">Assessing the potential for luminescence dating of basalts.</a> Quaternary Geochronology. 6, 61-70 (2011).</li><li>Li, S. H., Chen, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Studies+of+thermal+stability+of+trapped+charges+associated+with+OSL+from+quartz.">Studies of thermal stability of trapped charges associated with OSL from quartz.</a> Journal of Physics D-Applied Physics. 34 (4), 493-498 (2001).</li><li>Fu, X., Li, S. H., Li, B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Optical+dating+of+aeolian+and+fluvial+sediments+in+north+Tian+Shan+range,+China:+Luminescence+characteristics+and+methodological+aspects.">Optical dating of aeolian and fluvial sediments in north Tian Shan range, China: Luminescence characteristics and methodological aspects.</a> Quaternary Geochronology. 30, 161-167 (2015).</li><li>Hu, G., Li, S. -. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Simplified+procedures+for+optical+dating+of+young+sediments+using+quartz.">Simplified procedures for optical dating of young sediments using quartz.</a> Quaternary Geochronology. 49, 31-38 (2019).</li><li>Porat, N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Use+of+magnetic+separation+for+purifying+quartz+for+luminescence+dating.">Use of magnetic separation for purifying quartz for luminescence dating.</a> Ancient TL. 24 (2), 33-36 (2006).</li><li>Mejdahl, V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Thermoluminescence+dating+of+sediments.">Thermoluminescence dating of sediments.</a> Radiation Protection Dosimetry. 17, 219-227 (1986).</li><li>Fain, J., Soumana, S., Montret, M., Miallier, D., Pilleyre, T., Sanzelle, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Luminescence+and+ESR+dating-Beta-dose+attenuation+for+various+grain+shapes+calculated+by+a+Monte-Carlo+method.">Luminescence and ESR dating-Beta-dose attenuation for various grain shapes calculated by a Monte-Carlo method.</a> Quaternary Science Reviews. 18, 231-234 (1999).</li><li>Prescott, J. R., Hutton, J. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cosmic+ray+contributions+to+dose+rates+for+luminescence+and+ESR+dating:+large+depths+and+long-term+time+variations.">Cosmic ray contributions to dose rates for luminescence and ESR dating: large depths and long-term time variations.</a> Radiation Measurements. 23, 497-500 (1994).</li><li>Peng, L., Forman, S. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=LDAC:+An+excel-based+program+for+luminescence+equivalent+dose+and+burial+age+calculations.">LDAC: An excel-based program for luminescence equivalent dose and burial age calculations.</a> Ancient TL. 37, 2 (2019).</li><li>Lafuente, B., Downs, R. T., Yang, H., Stone, N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+power+of+databases:+the+RRUFF+project.">The power of databases: the RRUFF project.</a> Highlights in Mineralogical Crystallography. , 1-30 (2015).</li><li>Wintle, A. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Luminescence+dating:+laboratory+procedures+and+protocols.">Luminescence dating: laboratory procedures and protocols.</a> Radiation Measurements. 27, 769-817 (1997).</li><li>Aitken, M. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Thermoluminescence Dating. , (1985).</li><li>Porat, N., Faerstein, G., Medialdea, A., Murray, A. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Re-examination+of+common+extraction+and+purification+methods+of+quartz+and+feldspar+for+luminescence+dating.">Re-examination of common extraction and purification methods of quartz and feldspar for luminescence dating.</a> Ancient TL. 33 (1), 22-30 (2015).</li><li>And&#242;, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Gravimetric+Separation+of+Heavy+Minerals+in+Sediments+and+Rocks.">Gravimetric Separation of Heavy Minerals in Sediments and Rocks.</a> Minerals. , 15 (2020).</li><li>Nelson, M., Rittenour, T., Cornachione, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Sampling+methods+for+luminescence+dating+of+subsurface+deposits+from+cores.">Sampling methods for luminescence dating of subsurface deposits from cores.</a> Methods and Protocols 2. 88, 1-15 (2019).</li><li>Munsell Color. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Munsell Soil Color Charts: with Genuine Munsell Color Chips. , (2010).</li><li>USDA Natural Resources Conservation Service Soils. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Keys to soil taxonomy. 20, (2014).</li><li>User Manual. Malvern Instruments Ltd Available from: <a target="_blank" href="https://www.malvernpanalytical.com/en/products/product-range/mastersizer-range/mastersizer-3000">https://www.malvernpanalytical.com/en/products/product-range/mastersizer-range/mastersizer-3000</a> (2013)</li><li>Wentworth, C. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+scale+of+grade+and+class+terms+for+clastic+sediments.">A scale of grade and class terms for clastic sediments.</a> Journal of Geology. 30 (5), 377-392 (1922).</li><li>Mejdahl, V., Christiansen, H. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Procedures+used+for+luminescence+dating+of+sediments.">Procedures used for luminescence dating of sediments.</a> Boreas. 13, 403-406 (1994).</li><li>Madsen, A. T., Duller, G. A. T., Donnelly, J. P., Roberts, H. M., Wintle, A. G. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Chronology+of+hurricane+landfalls+at+Little+Sippewisset+Marsh,+Massachusetts,+USA,+using+optical+dating.">Chronology of hurricane landfalls at Little Sippewisset Marsh, Massachusetts, USA, using optical dating.</a> Geomorphology. 109, 36-45 (2009).</li><li>Durcan, J. A., Duller, G. A. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+fast+ratio:+A+rapid+measure+for+testing+the+dominance+of+the+fast+component+in+the+initial+OSL+signal+from+quartz.">The fast ratio: A rapid measure for testing the dominance of the fast component in the initial OSL signal from quartz.</a> Radiation Measurements. 46, 1065-1072 (2011).</li><li>Wang, Y., Chen, T., Chongyi, E., An, F., Lai, Z., Zhao, L., Liu, X. -. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Quartz+OSL+and+K-feldspar+post-IR+IRSL+dating+of+loess+in+the+Huangshui+river+valley,+northeastern+Tibetan+plateau.">Quartz OSL and K-feldspar post-IR IRSL dating of loess in the Huangshui river valley, northeastern Tibetan plateau.</a> Aeolian Research. 33, 23-32 (2018).</li><li>Murray, A., Olley, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Precision+and+accuracy+in+the+optically+stimulated+luminescence+dating+of+sedimentary+quartz:+A+status+review.">Precision and accuracy in the optically stimulated luminescence dating of sedimentary quartz: A status review.</a> Geochronometria. 21, 1-16 (2002).</li><li>Murray, A. S., Wintle, A. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Luminescence+dating+of+quartz+using+an+improved+single-aliquot+regenerative-dose+protocol.">Luminescence dating of quartz using an improved single-aliquot regenerative-dose protocol.</a> Radiation Measurements. 32 (1), 57-73 (2000).</li><li>Timar-Gabor, A., Wintle, A. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=On+natural+and+laboratory+generated+dose+response+curves+for+quartz+of+different+grain+sizes+from+Romanian+loess.">On natural and laboratory generated dose response curves for quartz of different grain sizes from Romanian loess.</a> Quintenary Geochronology. 18, 34-40 (2013).</li></ol>

The Baylor University Geoluminescence Dating Research Laboratory, within the Dept. of Geosciences and the associated personal do not have any conflicts of interest or financial interest that can affect the design of experiments or analysis, protocols, outcomes of the research or educational activities conducted in the lab. This Lab, including all the technology within and software, is used solely to conduct research, discovery, education, and mentoring.

Quartz mineralogical purity is critical for OSL dating. However, quartz spectral purity is equally important and is usually enhanced with the careful concentration of quartz grains. Ideally, quartz grains under blue LED light (470 nm &#177; 20 nm) stimulation for 40 s should emit &#8805; 90% of the luminescence within the first ~0-2.5 s of stimulation, termed the fast component, with &#60; 10% of light emission between ~2.5 and ~15 s (medium component), and a final low emission post ~15 s, (slow component) (Figure 8). A luminescence emission dominated by a fast component is preferred because it is rapidly solar reset (in seconds) and shows high sensitivity to applied &#946; radiation in the laboratory, enhancing equivalent dose determinations. An important metric to assess the dominance of fast components for OSL dating of quartz is the calculation of a &#34;fast ratio&#34;29,30 with an example shown by Equation 2 and in Figure 8. A fast ratio of &#62;20 for quartz shine down curve is considered a robust luminescence emission suitable for OSL dating29 (see Figure 8A). Separates that have contamination with K-feldspars and plagioclase or feldspathic inclusions often yield fast ratios of &#60;10 (see Figure 8B,C) and are unsuitable for SAR quartz dating protocols.
Fast Ratio <img alt="Equation 2" src="/files/ftp_upload/62706/62706eq02.jpg" /> (Equation 2)
Where L1: Fast component emission for ~0-2.5 s 
L2: Medium component emission ~2.5-15 s L3: Slow component emission ~ 15-40 s
An important test on the spectral purity of isolated quartz grains is the response of aliquots to infrared excitation from LEDs (845 nm &#177; 4 nm). Most quartz grains yield a low or negligible luminescence emission with IR stimulation at or within a few hundred counts of background emissions. A metric has been developed to assess IR-based emissions, called the IR depletion ratio, which is calculated as a SAR ratio (Lx/Tx) for irradiated (5-10 Gy) quartz grains stimulated with IR LEDs and then blue LEDs. Specifically, the ratio of IR luminescence divided by blue emissions should be &#60;5%, which indicates a spectrally pure quartz fraction amenable for OSL dating (Figure 8A). However, there are instances that mineralogically pure quartz grains can yield errant luminescence emissions with IR stimulation. This IR signal may reflect adhering lithic fragments or feldspathic inclusions in quartz. In such instances, quartz grains should be dated by feldspar protocols31. These protocols with modifications can be used to separate and confirm the purity of other minerals for OSL dating, such as k-feldspar, plagioclase, and olivine and pyroxene for other planetary applications.
The ability to isolate a &#62;99% quartz separate and confirm the purity at the grain level is a prerequisite for accurate luminescence dating. Single-grain and ultra-small aliquot (10-50 grains) dating requires additional verification that the luminescence emissions of all grains were from quartz. In turn, the application of thermal transfer approaches that can yield credible OSL ages up to one million years is predicated on pure quartz signals from mineral grains6. A mono-mineralogic quartz separate is foundational for applying OSL-SAR protocols, which provides a sequence of ages for deciphering the depositional history of eolian and fluvial systems for the late Quaternary1,2,32,33 (Figure 1 and Figure 2). Contamination of quartz aliquots by the errant K-feldspar grains or feldspathic inclusions in quartz or adhering lithic fragment yields a mixed dosimetric signal and prone to anomalous fading often yields underestimates4. However, a pure quartz separate does not absolutely ensure spectral purity and appropriate emissions for quartz dating. Effective OSL dating requires careful and complete isolation of quartz grains and OSL associated metrics to verify a pure quartz separate mineralogically and spectrally2,33,34.

Optically stimulated luminescence (OSL) geochronology yields the time from the last light or heat exposure after sediment erosion, deposition and burial; and further exposure to light or heat. Thus, natural sedimentary processes or heating events (&#62;300 &#176;C) reduces the previously inherited luminescence signal to a consistently low level. In the past two decades, there have been substantial advances in luminescence dating, such as single aliquot and grain analysis of specific mineral grains, like quartz. These experiment-based dating protocols with blue or green diodes can compensate effectively for sensitivity changes induced in the laboratory, rendering OSL ages for the past ca. 500 ka1,2,3.
Silicate minerals such as quartz and potassium feldspar have varying crystal lattice-charge defects; some formed at the time of mineral crystallization and others due to subsequent exposure to ionizing radiation, resulting in geochronometric potential. These defects are probable locations of electron storage with trap-depth energies of ~1.3-3 eV. A subpopulation of contained electrons in lattice-charge defects of quartz grains is a source for time-diagnostic luminescence emissions with excitation by blue light. Thus, this luminescence emission increases with time, above the solar or heat reset level with exposure to ionizing radiation during the burial period. This signal is reduced to a low, definable level (&#34;zeroed&#34;) with subsequent sunlight exposure with sediment erosion, transport, and deposition. This luminescence &#34;cycle&#34; occurs in most depositional environments on Earth and other planets. Thus, OSL dating of sedimentary quartz grains provides a depositional age, reflecting the time elapsed since the last light exposure with deposition and burial (Figure 1).
Luminescence dating is a dosimetric-based technique that yields age estimates for selected mineral grains, like quartz, from eolian, fluvial, lacustrine, marine, and colluvial sediments associated with enumerable contexts for geomorphic, tectonic, paleontologic, paleoclimatic, and archaeologic research2,4,5,6,7. OSL dating is also being evaluated to constrain surface processes on other planets, particularly on Mars8,9. Often, the most used mineral in OSL dating on Earth is quartz, reflecting its natural abundance, an inherent sensitivity as a geochronometer, signal stability, and rapid resetting with sunlight exposure (seconds to minutes)4,10,11,12. However, the accuracy of OSL dating is compromised if the quartz extract is impure, particularly if contaminated by potassium and other feldspars, which can have luminescence emissions ten to hundred-fold brighter than quartz and can yield age underestimates13. Therefore, the absolute (&#62;99%) purity for extracts of quartz grains from sediment is pivotal for accurate OSL dating. Thus, the focus of this contribution is to provide detailed procedures for isolating highly purified quartz grain separates from a variety of polymineral sediments. This requires integration of knowledge of mineralogy, crystal chemistry; optical and Raman imaging, to effectively apply laboratory protocols, to render OSL ages on quartz grains from carefully sampled strata from retrieved sediment cores. The sediment cores were collected by a push and percussion coring method, which retrieved intact sediment down to a depth of 20-25 m.
The OSL time-sensitive signal is reset relatively rapidly with minutes to hours of sunlight exposure. The geological OSL signal accumulates from this solar reset level. Although, the OSL emissions of quartz are considerably variable, reflecting original crystalline structure, lattice impurities, sensitization with luminescence resetting cycles14 (Figure 1). Thus, there is inherent variability in the dose sensitivity of quartz, and dating protocols need to be devised for specific mineralogic and sedimentary provenance. Fortunately, the emergence of single aliquot regenerative (SAR) dose protocols for quartz1,2 yielded systematics to redress variability in the OSL emissions and metrics to evaluate laboratory changes in apparent OSL sensitivity. Sediment grains function as long-term radiation dosimeters when concealed from further light exposure, with the luminescence signal serving as a measure of radiation exposure during the burial period. The radiation dose that is equivalent to the natural luminescence emission of isolated quartz grains is referred to as the equivalent dose (De: in grays, Gy), which is the numerator of the OSL age equation (Equation 1). The denominator is the Dose rate (Dr: Grays/yr.), defined by contributing &#945;, &#946;, and &#947; radiation, originating from the radioactive decay of daughter isotopes in the 235U, 238U, 232Th decay series, 40K, and with lesser contributions from the decay of 85Rb and cosmic and galactic sources.
OSL age (yr) = <img alt="Equation 1" src="/files/ftp_upload/62706/62706eq01.jpg" /> (Equation 1)
Where, D&#945;&#160;= alpha dose D&#946; = beta dose D&#947; = gamma dose Dc = cosmic dose and w=water attenuation factor.
Another method for U and Th determinations in the laboratory or the field is gamma spectrometry, with the Germanium variant able to quantify U and Th isotopic disequilibrium with suitable adjustments to the dose rate. The beta and gamma components of the environmental dose rate need to be modified for mass attenuation15. However, there is an effectively insignificant alpha dose for grains &#62;50 &#181;m with the outer 10-20 &#181;m of grains removed by treatment with undiluted HF during preparation. A critical component in dose rate assessment is the quantification of the cosmic and galactic dose during the burial period, which is calculated for specific points on Earth with adjustments for longitude, latitude, elevation, burial depth, and density of overlying sediment16,17.
Sediments that contain &#62;15% quartz are usually relatively straightforward for separating out a high purity quartz fraction. However, sediments with &#60;15% quartz often require added time to ensure needed mineralogic purity for OSL dating. Approximately 500-1000 quartz grains are needed for this analysis, but often thousands of grains are separated for duplicate analyses, archiving to expand a calibration library, and future advancements. The mineralogic composition of sediment samples is initially assessed, grain by grain, by petrographic analysis through a binocular microscopic (10-20x) and associated imagine analysis. The mineralogy of individual grains is tested further by Raman spectroscopy to measure grain spectra using an excitation laser (455 nm, 532 nm, 633 nm, or 785 nm) and statistically compare grain emissions to known mineral spectra from the RRUFF System Database18.
Once the visual and spectral inspection is satisfactory, the purity of the OSL signal is further checked, utilizing an automated luminescence reader system. Three to five aliquots of the sample are exposed to infrared excitation (IR = 1.08 watts at 845 nm &#177; 4 nm), which preferentially stimulates feldspar minerals, and this emission is compared to emissions by blue light excitation (Bl = 470 nm &#177; 20 nm), which preferentially stimulates quartz. If the ratio IR/Bl &#8805; 5%, the test indicates feldspar contamination and acid digestions are repeated. If the ratio IR/Bl &#60;5%, then the samples are deemed quartz fraction satisfactorily for dating.
Single aliquot regeneration (SAR) protocols on quartz grains is an often-used approach in OSL dating sediments with procedures tailored for a specific sample, a study site, or an area. The reproducibility of these protocols is determined by giving quartz grains a known beta dose (e.g., 30 Gy) and evaluating what heat pretreatment recovers this known dose (Figure 2). In practice, determining a De with the SAR protocols involves the calculation of a ratio between the natural luminescence and the luminescence from a known test dose (Ln/Tn ratio), which is compared to the luminescence emissions for regenerative doses divided by the luminescence from the same test dose (Lx/Tx) (Figure 2). A correction, a consistently applied test-dose (e.g., 5 Gy), has been devised to compensate for quartz grain(s) sensitivity changes with measurement through SAR cycles. Often the OSL emissions increase by &#62;5% with each successive SAR cycle, though given the same dose (e.g., 5 Gy)7.
At least forty aliquots of quartz or 500 grains are analyzed with TL/OSL reader system, with blue light excitation. The luminescence data generated is analyzed by software associated with the Ris&#248; TL/OSL-DA-20 reader system. The De and Dr values and age estimates are calculated using the Luminescence Dose and Age Calculator (LDAC)17. This platform applies statistical models to determine equivalent dose (De) values and render corresponding OSL age with constrained errors.
The extracted light-shielded sample from a core is prepared for two reasons: 1) To obtain a mineralogic fraction of quartz grains with a purity of &#62;99%, and 2) To isolate grains of specific size fraction, e.g., 150-250 &#181;m, for assessment of the environmental Dr for OSL dating17. In many sedimentary settings, quartz grains are common; but mixed with other silicate and non-silicate minerals, rock fragments, and organic matter. Previously, procedures were briefly outlined, indicating some specific steps and reagents needed to isolate pure quartz grains in the context of OSL dating 13,19,20,21,22,23. This contribution has benefited greatly from these previous approaches. This paper outlines revised, and more detailed protocols using petrographic imaging and Raman technology to monitor grain mineralogy and render highly pure (&#62;99%) quartz extracts for luminescence dating. These quartz isolation protocols have been developed after preparing hundreds of samples from diverse geological environments in the Americas, Eurasia, China, and Africain, the Baylor Geoluminescence Dating Research Laboratory, reflecting analytical experience over thirty years, and are not definitive methods, with suitable variations used by other labs. These are not static protocols, and modifications and additions for improvement are welcomed.

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			<td>100 mL graduate cylinder</td>
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			<td>Macro-Core</td>
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			<td>Analytical balance</td>
			<td>Sartorius 1207 MP2</td>
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isolation of quartz grains for optically stimulated luminescence (osl) dating of quaternary sediments for paleoenvironmental research

Optically stimulated luminescence (OSL) dating quantifies the time since mineral grains were deposited and shielded from additional light or heat exposure, which effectively resets the luminescence clock. The systematics of OSL dating is based on the dosimetric properties of common minerals, like quartz and feldspar. The acquired luminescence with exposure to natural ionizing radiation after burial provides a depositional age for many Quaternary sedimentary systems, spanning the past 0.5 Ma. This contribution details the procedures for separating pure quartz grains of a known range of particle sizes to facilitate luminescence analysis with small or single grain aliquots. Specifically, protocols are given for the needed data and interpretations for effective OSL dating of terrestrial sediment cores or sample tubes from exposures. These cores, 5-20 m long in 1.2 m sections, are split lengthwise and crown-cut leaving 80% of core volume undisturbed, which facilitates sampling of light-protected sediment for OSL dating deep within the core. Sediment samples are then subjected to a series of physical separations to obtain a certain grain-size interval (e.g., 150-250 &#181;m). Magnetic minerals are removed in wet and dry states using magnets. A series of chemical digestions starts with soaking in H2O2 to remove organic matter, followed by HCl exposure to remove carbonate minerals, followed by density separation. Subsequently, grains are soaked in HF for 80 min and after in HCl to render solely quartz grains. The mineralogic purity (&#62;99%) of the quartz extract is quantified with grain petrographic assessment and Raman spectroscopy. Repeating this quartz isolation procedure may be necessary with sediment that contains &#60;15% quartz grains. Excitation of the purified quartz grains by LED-derived blue and IR light allows calculations of the fast and IR depletion ratios, which are metrics to assess the dominance of luminescence emissions from quartz.

The laboratory procedures outlined are focused on enhancing the separation of pure quartz grains (700 to 50 &#181;m size) needed for OSL dating without inadvertent light resetting in the laboratory (Figure 1). A pure quartz separate, mineralogically and optically, is a prerequisite for applying SAR and TT-OSL dating procedures (Figure 2). These procedures explain the necessary steps for effectively understanding and sampling continuous sediment cores, avoiding zones of pedogenesis and diagenesis, retrieving unlight-exposed sediments from cores (Figure 3 and Figure 4); to isolate quartz grains for OSL dating protocols to constrain the timing of sediment deposition in the past ca. 500 ka (Figure 5). The mineralogy of grains of the unprepared sample and prepared separates are assessed continuously through the preparation process to identify the contaminating mineralogy and actively assess the process of removal of unwanted minerals (Figure 6 and Figure 7). The quartz mineralogic purity is determined for subset grains (100-400) through binocular microscopic inspection (10-20x) and by Raman spectroscopy. The use of this technology and prerequisite knowledge is vital to assess and confirm the needed purity (&#62;99%) of quartz separations for OSL dating (Figure 8).
The process for quartz separation is started with the removal of organic matter with H2O2 and then the subsequent purging of Ca/MgCO3 with soaking in HCl. Subsequently, a size fraction is designated by sieving with disposable nylon mesh (e.g., 150 and 250 &#181;m), which is necessary for calculating dose rate values (in mGy/y) (Figure 6A inset). The purity of the quartz separate is enhanced by two density separations at 2.6 and 2.7 g/cc, the bounding density of quartz (Figure 6B inset). The subsequent soaking of sized grains in HF for 80 min removes non-quartz minerals. This treatment also etches the outer 10-20 &#181;m of grains to remove the alpha-dose affected area, simplifying dose rate calculations (Figure 6). The purity of the quartz separate is never assumed but assessed through binocular microscopic inspection and Raman-based measurements at the end of grain separation. Density separations and/or HF treatment can be repeated to rid the separate contaminating grains if a representative aliquot contains &#62;1% non-quartz grains, particularly feldspar minerals (Figure 7). The quartz purification procedure was repeated up to four times with quartz contents of &#60;15% to render shine down curves with a fast ratio of &#62;20, characteristic of pure quartz (Figure 8).
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/62706/62706fig01.jpg" /> 
Figure 1: Processes with OSL dating. (A) Mineral grains acquire OSL with ionizing radiation exposure. (B) Grain OSL is reset by sunlight with erosion/ transport. (C) Exposure to ionizing with burial; luminescence acquired. (D) Light exposure resets OSL with erosion/ transport. (E) Grains are re-buried, and OSL is acquired with exposure to ionizing radiation. (F) Shows sampling without light exposure. The resultant measured natural OSL is followed by a normalizing test dose (Ln/Tn) which is equated to the regenerative dose curve to yield an equivalent dose (De). This figure has been modified from Forman, S. L. et al.7. <a href="https://www.jove.com/files/ftp_upload/62706/62706fig01large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/62706/62706fig02.jpg" /> 
Figure 2: Optical Stimulating Luminescence- Single Aliquot Regeneration (OSL-SAR) protocols for quartz grains. (A) Equivalent dose using SAR protocols; the natural OSL is Ln/Tn, and the regenerative dose is Lx/Tx; sensitivity changes are corrected by giving a test dose (e.g., 5 Gy). (B) Generalized SAR protocol. This figure has been modified from Forman, S. L. et al.7. <a href="https://www.jove.com/files/ftp_upload/62706/62706fig02large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/62706/62706fig03.jpg" /> 
Figure 3: Flow diagram outlining the steps necessary to open, describe, and interpret a recovered sediment core. This figure shows retrieval of sediment core using percussion corer, followed by the opening, cleaning, description, and study of the core to obtain the optimal sample for OSL dating. <a href="https://www.jove.com/files/ftp_upload/62706/62706fig03large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/62706/62706fig04.jpg" /> 
Figure 4: Example of a typical log of a core sedimentary and stratigraphic section. Units and pedosedimentary facies are defined using sedimentology, stratigraphy, pedology, granulometry, and carbonate percentage. The soils horizons found in the stratigraphic column from top to bottom are: A: Surface organic-rich horizon, B: subsoil with weak structure and color (Bw), and buried B horizon Btb with clay accumulation, Btkb with secondary calcium carbonate and clay accumulation, and Bkb with an accumulation of secondary calcium carbonate. The dominant particle size of sedimentary units is shown on the lower horizontal with medium sand (MS), fine sand (FS), very fine sand (VFS), and Silt (Si). <a href="https://www.jove.com/files/ftp_upload/62706/62706fig04large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 5" class="xfigimg" src="/files/ftp_upload/62706/62706fig5v2.jpg" /> 
Figure 5: Flow diagram for the steps necessary to collect an OSL sample from a sediment core. This figure presents a flow diagram with the main steps followed to prepare a quartz separate for OSL dating. The protocols start with the extraction of a polymineral sediment from light-shielded areas of the core in the light safe OLS lab. They continue with the extraction of the mono-mineralogic fraction of quartz, comprising the removal of organic matter with peroxide, carbonates with HCl, and magnetic minerals using hand magnets. The separation of the specific fraction of sand-size sediment is done by sieving; separation of minerals less dense and heavier than quartz is done using density liquids (&#961; = 2.6 g/cc and 2.7 g/cc). The final steps of cleaning require immersion of the sediment into HF and HCl full strength to isolate quartz from any other mineral in the fraction. The purity of the separate is evaluated by binocular inspection, RAMAN spectroscopy, and further verification of IRSL (Infrared) emissions. The goal is to obtain a sample with a purity &#8805;99%. Failure to do so requires that some of the steps must be repeated.<a href="https://www.jove.com/files/ftp_upload/62706/62706fig5v2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 6" class="xfigimg" src="/files/ftp_upload/62706/62706fig06.jpg" /> 
Figure 6: Flow chart depicting all the steps necessary to obtain a pristine quartz separate from a sediment sample from a core. This clean quartz fraction will be used for OSL-SAR analyses for age assessment. <a href="https://www.jove.com/files/ftp_upload/62706/62706fig06large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 7" class="xfigimg" src="/files/ftp_upload/62706/62706fig07.jpg" /> 
Figure 7:&#160;Comparison of two samples collected in two different areas: White Sands (first row) and Mongolia (second row). Column A shows raw samples under the binocular microscope, as collected in the field. Column B shows the separate fractions for each processed samples, under the binocular microscope. Column C shows the corresponding RAMAN spectroscopy results. The sample from White Sands contains sulfates (mainly gypsum), halides, and very little quartz (column A). Correspondently, the separate fraction (63-100 &#181;m) for the processed sample in a Column B&#160;shows that it contains mostly quartz, still with some vestiges of gypsum, as shown by the RAMAN Spectroscopy in Column C. The ratio between the OSL IR and blue responses for this sample is 9%, confirming that it needs a second separation in density at 2.6 g/cc, which possibly will remove the lighter gypsum (2.36 g/cc) from heavier quartz. Contrastingly, the Mongolian sample (Column A) is initially very rich in feldspars, predominantly K-feldspar. After undergoing the cleaning procedures, shows abundant quartz isolated in the 100-150 &#181;m separate (Columns B and C), rendering a satisfactory IR/Bl ratio of 3.7%.&#160;<a href="https://www.jove.com/files/ftp_upload/62706/62706fig07large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 8" class="xfigimg" src="/files/ftp_upload/62706/62706fig08.jpg" /> 
Figure 8: Comparison of fast ratio for the natural in three samples that represent different degrees of quartz fraction purity. (A) The ideal fast ratio distribution in a pristine eolian sample from Red River, with fast ratio= 72. Contrasting figures (Figure 8B,C) have a less fast component with blue LED stimulation, which is below 20. (B) A sample with incomplete quartz and plagioclases separation. The L2 and L3 components are a significant % of the L1 component (see Equation 2). (C) A shine-down curve for feldspathic quartz, with a dominant medium component (L2). <a href="https://www.jove.com/files/ftp_upload/62706/62706fig08large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about Isolation of Quartz Grains for Optically Stimulated Luminescence OSL Dating of Quaternary Sediments for Paleoenvironmental Research at JoVE.com

Isolation of Quartz Grains for Optically Stimulated Luminescence OSL Dating of Quaternary Sediments for Paleoenvironmental Research

This protocol is for the isolation of quartz grains by size for luminescence dating of sediments. Outlined are physical cleansing and chemical digestions by soaking sequentially in H2O2, HCl, HF, and HCl again to isolate quartz grains. The quartz purity is quantified with microscopic assessment, Raman spectroscopy, and IR depletion ratio.

Isolation of Quartz Grains for Optically Stimulated Luminescence (OSL) Dating of Quaternary Sediments for Paleoenvironmental Research

Optically stimulated luminescence (OSL) dating quantifies the time since mineral grains were deposited and shielded from additional light or heat ...

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