(above image: undertaking a geophysical survey of hearths at Lake Mungo)
Magnetic Susceptibility (MS) measurements of archaeological deposits and cave sediments. MS can be used to understand a range of processes, both natural and anthropogenic, on archaeological sites:
– identification of combustion features (hearths, fire use) and ash fuel sources.
– palaeoclimatic reconstruction
– sediment sourcing
MS is a low cost and rapid way of examining changes in iron mineral concentrations in sediments. It is conducted on around 10 grams of sediment (air dried and sieved to remove large non-magnetic clasts). This analysis can be conducted on samples taken during excavation or on stored representative bulk samples and can be collected in standard sample bags but preferably without using metal tools.
Mineral Magnetic Analysis (MMA) can be conducted on sediments to understand MS variation on archaeological sites and cave sediments. These methods help to identify the magnetic minerals present, their magnetic grain size and concentrations. In addition to helping elucidate if the MS signal is showing evidence for anthropogenic alteration, palaeoclimate and sediment sourcing it can also be used to help source archaeological artefacts. This is conducted on the same samples as the MS analysis.
Palaeomagnetic analysis (Pmag) is undertaken on samples to understand:
– Chronology over the last 4 billion years. The resolution provided will depend on the time period and region under investigation.
– Thermomagnetic history (heat treatment) and maximum heating temperature of rocks and stone tools.
Samples generally need to be oriented towards north using a sun compass or magnetic compass, however, certain types of analysis (heat treatment investigations and geomagnetic field strength reconstructions) do not need to be oriented. For more detailes of how to sample for Pmag analysis see: COMING SOON.