QUARTZ LUMINESCENCE SENSITIVITY: A FINGERPRINT OF FIRE EXPOSURE AND RESIDENCE TIME WITHIN THE CRITICAL ZONE

Luminescence sensitivity of quartz, recorded as the brightness of signal generated per applied dose of radiation, has been shown to vary between geologic terrains and rock types, providing a promising tool for provenance analysis. However, observations also suggest that quartz sensitivity may be enhanced by sediment-transport, exposure to fire and bio-physio-chemical weathering within the critical zone. Although the mechanisms that generate quartz sensitization are not fully understood, we provide data suggesting that longer residence time within the critical zone leads to enhanced quartz sensitivity, likely due to greater cumulative heat and light exposure of grains. The repeated exposure to optical, mechanical, and thermal energy can release trapped charge from strongly held traps (defects) and open geologically filled recombination centers within the crystal lattice, enhancing luminescence sensitivity. We provide a global survey of quartz sensitivity across a range of geologic and climatic settings (>2000 samples) to identify common factors linked to the magnitude of sensitivity from each site (measured as photons released/volume of sand/given dose). Small study sites Utah and Arizona are explored to test the influence of fire exposure and residence time within the critical zone on quartz sensitivity. Results suggest burn severity and rates of sediment generation linked to climate-mediated soil thickness and weathering processes impart a large influence on quartz luminescence sensitivity.