Osl dating archaeology

18-Oct-2017 20:43

Ensuing research in the 1970s documented that marine and other sediments with a prior sunlight exposure of hours to days were suitable for thermoluminescence dating (Wintle and Huntley, 1980).Discoveries in the 1980s and 1990s that exposure of quartz and feldspar grains to a tunable light source, initially with lasers and later by light emitting diodes, yield luminescence components that are solar reset within seconds to minutes, expanded greatly the utility of the method (Huntley et al., 1985; Hütt et al., 1988; Aitken, 1998).(f) Careful sampling without light exposure and measuring of the natural luminescence, followed by a normalizing test dose (Ln/Tn) compared to the regenerative dose to yield an equivalent dose (De) (from Mellet, 2013).The exposure of quartz and feldspar grains to sunlight for 60 seconds effectively diminishes the time-stored OSL signal to a low definable level.95% reduction in OSL within 4 seconds of exposure to light from blue diodes Optically stimulated luminescence (OSL) dating or optical dating provides a measure of time since sediment grains were deposited and shielded from further light or heat exposure, which often effectively resets the luminescence signal (Fig.1).This technique, as thermoluminescence, was originally developed in the 1950s and 1960s to date fired archaeological materials, like ceramics (Aitken, 1985).

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The radioactive decay of 40K releases beta and gamma radiation, whereas the decay in the U and Th series generates mostly alpha particles and some beta and gamma radiation.Exposure of mineral grains to light or heat (at least 300˚C) reduces the luminescence to a low and definable residual level.Often this luminescence “cycle" occurs repeatedly in many depositional environments with signal acquisition of mineral grains by exposure to ionizing radiation during the burial period and signal resetting (“zeroing") with light exposure concurrent to sediment erosion and transportation. (a) Luminescence is acquired in mineral grains with exposure to ionizing radiation and trapping of electrons.In this paper we present a new technique using luminescence field profiling coupled with OSL dating to produce complete (relative) sequences of dates for sedimentary stratigraphies associated with agricultural terraces and earthworks.

The method is demonstrated through a series of case-studies in western Catalonia, Spain, in which we reconstruct the formation sequence of earthwork features from the Middle Ages through to the present day.

This residual level is the point from which the geological OSL signal accumulates post burial.