Exploring the application of blue and red thermoluminescence for dating volcanic glasses

Abstract

Tephras are significant markers in the stratigraphic record and play a key role in establishing paleoenvironmental and paleoclimate histories worldwide. Despite burgeoning research focused on tephra characterization and correlation techniques, there are still few techniques that allow for the direct dating of tephra, particularly below the lower age limit of K/Ar and Ar/Ar dating methods. In this study, we test different thermoluminescence (TL) dating approaches on the 4–11 μm volcanic glass constituents of three different independently different tephras. By comparing against independent age control, we demonstrate the utility of both blue (320–450 nm) and red (587–651 nm) TL emissions for dating volcanic glasses using single aliquot regenerative (SAR) dose techniques. We find that both blue and red TL emissions from the volcanic glass shards are dim but reproducible and show no evidence for significant sensitivity changes occurring between the natural TL and the first test dose during the SAR protocol. Fading tests on the blue TL signal show that g-values range from 1.6 ± 1.0 to 2.9 ± 1.1%/decade and are statistically indistinguishable with zero at 2σ for the red TL. Bleaching experiments show that both blue and red TL signals are sensitive to light exposure, with sensitivity corrected signals declining by ∼40% over a 2-h period. For all three tephras, both the fading-corrected blue and red SAR-TL ages are consistent with age expectation. These successful results demonstrate the effectiveness of TL techniques for determining the eruption ages of tephra deposits in primary position between ∼1 and at least 30 ka.