Developments in archaeomagnetic dating in britain
In addition he is interested in archaeomagnetic dating, instrumental development and shallow geophysical prospection.
Archaeomagnetism is a method for dating fired materials and sediments from archaeological sites, based on changes of the Earth’s magnetic field in the past.
Samples of robust fired materials are usually taken by attaching a 25mm flanged plastic reference button to a cleaned stable area of the feature using a fast setting epoxy resin or encasing part of the feature in plaster of Paris (Clark 1988).
Sediments and friable fired materials are sampled by insertion of 25mm diameter plastic cylinders.
Magnetometers used are sufficiently sensitive for only small samples (c.
1cm3) to be required; approximately 15 samples are needed from each feature and it may be possible to select sampling location to minimise the visual impact if the feature is to be preserved.
Suitable archaeological features would include hearths, kilns and other fired structures.
Sediments may acquire a datable detrital remanent magnetisation from the alignment of their magnetic grains by the ambient field during deposition.
As the geomagnetic field has occasionally had the same direction at two different times, it is also possible to obtain two or more alternative dates for a single archaeological event.
In most case the archaeological evidence can be used to select the most likely of these.
The feature was above the hillfort’s ramparts, but below what looked like a Medieval field boundary.