QUARTZ AS A RECORDER OF FIRE INTENSITY: A NEW PROXY RECORD FROM QUARTZ LUMINSCENCE INTENSITY

The luminescence sensitivity of quartz (brightness per applied dose) has been shown to vary between geologic terrains and rock types and may be enhanced by weathering and sediment-transport history. Observations from laboratory thermal treatments and dating of archaeological hearths and pottery have illustrated increased quartz luminescence sensitivity in heated and fire-exposed sediments. We use these observations to test if there is a relationship between burn severity and luminescence sensitivity of soil samples from recent burn areas in the southwestern US. Samples from depth and outside the burn areas are used to determine the background (geologic) luminescence signature of the source-rock to compare against post-fire samples.

Results indicate enhanced quartz luminescence sensitivity of burned surface soils in comparison to samples from depth and outside of the burn perimeter. The relationship between sensitivity change and mapped soil-burn severity parameters suggest that burn intensity is recorded in the magnitude of quartz sensitivity change. The luminescence sensitivity signal and thermal activation characteristics of surface soils and burned rocks that were exposed to a high-severity fire are compared to the luminescence sensitivity from local soils outside the burn area. Results indicate that quartz luminescence sensitivity acts as a fingerprint of fire exposure in surface soils and can be used to assess past fire intensity.