Developments in archaeomagnetic dating in britain

22-Sep-2017 09:12

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 principles of the method are well established; see Linford (2006) and Zananiri et al. It has been used in Scotland from 1967 (Aitken and Hawley 1967) and is increasingly part of multi-method site chronologies.

The strengths of archaeomagnetic dating are that it dates fired clay and stone, for example hearths, kilns, ovens and furnaces, which occur frequently on archaeological sites; it dates the last use of features, providing a clear link to human activity; it is cost effective and is potentially most precise in periods where other dating methods, e.g. Archaeomagnetic dating is based on a comparison of the ancient geomagnetic field, as recorded by archaeological materials, with a dated record of changes in the Earth’s field over time in a particular geographical area, referred to as a secular variation curve.

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If we can take orientated samples back to the lab, we can tell what direction the magnetic field was pointing in when the feature last cooled down, “freezing in” the magnetisation.There are primarily two types of archaeological events which may result in the Earth’s magnetic at a particular moment being recorded by archaeological material: heating and deposition in air or water.If materials have been heated to a sufficiently high temperature (400°C) they may retain a thermoremament magnetisation, which reflects the Earth’s magnetic field at the time of last cooling.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.

If we can take orientated samples back to the lab, we can tell what direction the magnetic field was pointing in when the feature last cooled down, “freezing in” the magnetisation.There are primarily two types of archaeological events which may result in the Earth’s magnetic at a particular moment being recorded by archaeological material: heating and deposition in air or water.If materials have been heated to a sufficiently high temperature (400°C) they may retain a thermoremament magnetisation, which reflects the Earth’s magnetic field at the time of last cooling.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.In addition he is interested in archaeomagnetic dating, instrumental development and shallow geophysical prospection.