HR: 0800h
AN: GP21A-14    [Abstracts]
TI: Magnetic Mineralogical Transformations in Experimental Fires and Implications to Archaeomagnetic Studies
AU: Carrancho, A
EM: acarrancho@beca.ubu.es
AF: Universidad de Burgos, Departamento de Física - Universidad de Burgos E.Politécnica Superior, Avda. Cantabria S/N, Burgos, 09006, Spain
AU: * Villalain, J J
EM: villa@ubu.es
AF: Universidad de Burgos, Departamento de Física - Universidad de Burgos E.Politécnica Superior, Avda. Cantabria S/N, Burgos, 09006, Spain
AU: Calvo, M
EM: mcalvo@ubu.es
AF: Universidad de Burgos, Departamento de Física - Universidad de Burgos E.Politécnica Superior, Avda. Cantabria S/N, Burgos, 09006, Spain
AB: It is well known that fire is a primary mechanism responsible for the magnetic enhancement experimented by iron minerals in soils. However, these mineralogical transformations involve complex processes highly dependent of factors like availability of pre-existing iron minerals, degree of heating, fuel employed or heat penetration with depth that strongly influence the final magnetic signal. We present here the results obtained from experimental fires conducted in the field with the objective to get a better understanding of the magnetic mineral transformations due to burning, emphasizing the direct implications for archaeomagnetism and archaeological research. During four days twice per day, a clay soil matrix was burned to temperatures ranging from 400ºC to 650ºC approximately. The temperatures were recorded with an array of thermocouples disposed along the surface and at different depths. Oriented and bulk samples were extracted before and after carrying out the heating in order to perform a complete set of magnetic mineral analyses. Both thermal and alternating field demagnetization were performed as well as several rock-magnetic measurements such as magnetic susceptibility, hysteresis cycles, Isothermal remanent magnetization (IRM) and backfield curves (± 2T), FORCS, Thermomagnetic curves and the analyses of the IRM coercivity components. We conclude that burning produce the reduction of a weak antiferromagnetic mineral (hematite) to a strong ferrimagnetic phase (magnetite). Mineralogical changes are focused to a limited depth (approx. up to 5 cm) but are particularly effective in the first 2-3 cm. where single-domain magnetite is noticeable. The record of p-TRMs and TRMs is a valuable tool in the identification of fires in archaeological contexts, but the changes in composition, concentration and granulometry of magnetic minerals can be also used as effective criterion in the study of fire. Understanding these processes and their effects is decisive in order to carry out archaeomagnetic analyses on fired archaeological materials.
DE: 1503 Archeomagnetism
DE: 1512 Environmental magnetism
DE: 1519 Magnetic mineralogy and petrology
DE: 1521 Paleointensity
DE: 1540 Rock and mineral magnetism
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2007 Joint Assembly