Santorini: Luminescence dating of a volcanic province using quartz?

Abstract

We have investigated the application of luminescence dating to the palaeosol underlying the Cape Riva ignimbrite from the volcanic island of Santorini (36.40°N, 25.40°E) in the Aegean Sea. The history of volcanism in this area is of intrinsic interest, and is also of importance to archaeology in the eastern Mediterranean — a flourishing late Bronze Age settlement was buried under the volcanic products of the Minoan Eruption (1640 BC). Volcanic provinces are notoriously difficult to date using luminescence techniques, because volcanic feldspars almost invariably show anomalous fading (which can lead to age underestimates of more than 50%). Quartz does not show anomalous fading, but unfortunately it is rare or non-existent in volcanic sediments, and so it is usually not considered as a potential chronometer. We have studied the luminescence characteristics of material extracted from the Cape Riva palaeosol, with good independent age control. All samples contain detectable quartz, but usually <0.01% of the bulk deposit; the quartz is identified primarily by the ability to sensitize the characteristic 110°C TL peak, and by the absence of significant regenerated response to intense infra-red illumination from an IR laser. It may be that this quartz is of aeolian origin, perhaps from North Africa or from local sources. If the former, quartz is only accumulated during the period of soil development. Blue-light (470 nm) stimulated luminescence signal levels are highly variable, and despite chemical and physical concentration, some aliquots show no significant natural luminescence or laboratory dose-response. The single-aliquot regenerative-dose protocol has been used to estimate the equivalent dose in the remainder. Despite our identification of the luminescent material as quartz, all aliquots grossly underestimate the known age, by 90% on average.