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Luminescence Dating
Luminescence Dating
Luminescence dating seeks to determine the time at which a rock was last exposed to sunlight or sufficient heating. Over time, electrons can become trapped inside defects of the crystal lattices of certain minerals. When the samples are heated or otherwise stimulated by light, a luminescence signal (photon) is released as the byproduct of the unstable electron being released (Rhodes, 2011). These photons can be quantified and if the rate of electron accumulation is known, dates can be calculated. The calculated date for a sample will refer to the time the sample was last bleached, or emptied of electrons, by exposure to light. Measuring photons must be done in the dark with extremely sensitive equipment (Bierman & Montgomery, 2020).
Luminescence dating is particularly useful when there is a lack of organic material available for dating, such as in water or wind-deposited sediments. This dating method is effective over time scales ranging from centuries to hundreds of thousands of years, depending on the sample. Improvements to luminescence dating are constantly pushing this time scale back, and it's now possible to use this technique on some samples dating back almost one million years. Luminescence dating is useful for surface process studies because it tracks the exposure history of mineral grains (Bierman & Montgomery, 2020). Luminescence dating is also used in archaeology to date artifacts like pottery and the surfaces of buildings or walls (Seely, 1975).
Cartoon depicting photons being emitted by Hannah Bonner Speech bubble text by Emily Mischler
Lee, M.K., Lee, Y.I., Lim, H.S. et al. (2011). Comparison of radiocarbon and OSL dating methods for a Late Quaternary sediment core from Lake Ulaan, Mongolia. J Paleolimnol 45, 127–135 https://doi.org/10.1007/s10933-010-9484-7
In this study, the researchers compared radiocarbon and luminescence dating methods to determine which one was most suitable for establishing a chronology of sediments from Lake Ulaan in southern Mongolia. In samples from the late Pleistocene and the early to late Holocene, the radiocarbon dating method calculated older ages than luminescence dating. It was determined that the older radiocarbon ages were a consequence of the influx of 14C-deficient carbon delivered from adjacent soils and rocks by westerly winds. This process is still active today. Late Pleistocene samples were also found to have been influenced by old carbon from deglacial meltwater. The results of the study suggest that when aeolian transport is involved, luminescence dating is superior to radiocarbon dating because it eliminates a common "old-carbon" error.
Tsukamoto, S., Asahi, K., Watanabe, T., & Rink, W. (2002). Timing of past glaciations in Kanchenjunga Himal, Nepal by optically stimulated luminescence dating of tills. Quaternary International, 97-98, 57-67. doi:10.1016/s1040-6182(02)00051-4
This study dated glacial sediments using optically stimulated luminescence and from there determined the ages of past glacial advances in Kanchenjunga Himal, eastern Nepal. Glacial sediment samples were collected from four different moraines and quartz grains were extracted from the samples. The researchers found that the quartz and feldspar minerals in supraglacial meltout tills were probably fully bleached before they were deposited. This bleaching likely occurred while glacier debris was being transported on the glacier. The resulting sample ages suggests that the glaciers expanded at 5-6, 8-10, and 20-21 thousand years ago.
Sources: Bierman, P. R., & Montgomery, D. R. (2020). Key concepts in geomorphology. New York, NY: Macmillan Learning.Lee, M.K., Lee, Y.I., Lim, H.S. et al. (2011). Comparison of radiocarbon and OSL dating methods for a Late Quaternary sediment core from Lake Ulaan, Mongolia. J Paleolimnol 45, 127–135 https://doi.org/10.1007/s10933-010-9484-7 Rhodes, E. J. (2011). Optically Stimulated Luminescence Dating of Sediments over the Past 200,000 Years. Annual Review of Earth and Planetary Sciences, 39(1), 461-488. doi:10.1146/annurev-earth-040610-133425 Seeley, MA. (1975). Thermoluminescent dating in its application to archaeology: A review. Journal of Archaeological Science. Volume 2, Issue 1. 17-43. https://doi.org/10.1016/0305-4403(75)90044-8. Tsukamoto, S., Asahi, K., Watanabe, T., & Rink, W. (2002). Timing of past glaciations in Kanchenjunga Himal, Nepal by optically stimulated luminescence dating of tills. Quaternary International, 97-98, 57-67. doi:10.1016/s1040-6182(02)00051-4
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