Optically stimulated luminescence (OSL) dating of an appropriate soil sample provides a measure of time from when the sediment grains in the soil sample were deposited and shielded from further light or heat exposure.
During the excavation of the Thirlestane square barrow, a soil sample was carefully taken from the edge of the ditch defining the barrow.
This was submitted to the School of Earth and Environmental Sciences at the University of St Andrews who undertook OSL dating that has now yielded a date from the surface of the square ditch surrounding the easternmost barrow at Thirlestane – AD 430 +/- 150.
This gives a maximum range of between AD 280 and AD 580, so it will be interesting to see what the radiocarbon dates from Tinnis are, and whether the fort overlaps in time with the square barrow.
The sample for OSL dating was taken from the left edge of the section through the ditch in the foreground in the photo below.
