Magnetic prospection on prehistoric sites in Western Canada

Abstract

Prehistoric sites in Western Canada present unusual conditions for magnetic prospection. Archaeological features are few and difficult to discern using standard prospection procedures. However, by addressing specific types of features, particularly fire hearths and fired rock and pottery, useful information about the cultural content of an archaeological site can be obtained. To secure comparative data, a number of replicative studies were conducted, with specific reference to determining a typical anomaly produced by the features. A small fire pit was kindled several times and repeatedly monitored with surveys using a single proton magnetometer. Fired rock received similar treatment. An in situ collection of local aboriginal pottery was also assayed. The experimental results indicated that fired rock will produce a detectable magnetic field after one firing, but a hearth must be rekindled at least three times to produce a significant anomaly. Pottery fragments also generate a small magnetic field which requires that the material be very close to the site surface to be discerned. The experiments also suggested that intepretation is enhanced by obtaining two magnetic readings per sensor station and using their difference to minimize ambient field fluctuations and natural magnetic variation caused by subsurface geology. The model data were used to interpret the results of a magnetic assessment of a large prehistoric campsite in Saskatchewan. Excavation results agreed well with the information provided by the predictive models. Two temporary dwelling remnants and two pottery vessels were exposed in areas determined to be magnetically significant. The magnetic assessment technique, when used to locate specific feature types, can be useful in prehistoric archaeological site assessment.

Magnetic detection of heated soils at paleolithic sites in Japan

“…Magnetite is formed through the reduction of hematite, and maghemite is formed from the breakdown of lepidocrocite (␥-FeOOH) (Thompson and Oldfield, 1986). The alteration (disappearance and formation) of magnetic minerals or heating process in itself changes the bulk magnetic properties of the rocks and soils (Le Borgne, 1960;Irving, 1964;Colani and Aitken, 1966;Tite and Mullins, 1971;Barbetti et al, 1977;Tarling, 1983;Barbetti, 1986;Bonhomme and Stanley, 1986;Gibson, 1986;Weymouth, 1986;Sternberg, 1987;Eighmy and Sternberg, 1990;Hathaway, 1990aHathaway, , 1990bHathaway et al, 1990;Smith, 1990;Bellomo, 1993). Therefore, a methodological approach using magnetic measurement of site remains has been conducted to identify the evidence of fire use by humans (Barbetti, 1986).…”

Metodologia geofísica aplicada ao estudo arqueológico dos sítios Bittencourt e Jambuaçu, Estado do Pará

“…Medidas do campo magnético terrestre são muito aplicadas na prospecção arqueológica, tanto por forneceremótimo resultado, como por serem rápidas e envolver custo baixo (Wynn, 1986a(Wynn, , 1986bGibson, 1986;Weymouth, 1986;Gaffney, 2008). Em trabalhos realizados na Amazônia este método tem produzido resultados excelentes, principalmente na Ilha de Marajó, conforme pode ser verificado em Alves (1979), Alves & Lourenço (1981), Roosevelt (1991), Barradas et al (1999) e Bevan & Roosevelt (2003.…”

The use of microgravity, magnetometry and resistivity surveys for the characterization and preservation of an archaeological site at Umm er‐Rasas, Jordan

“…Gravity anomalies over the architectural remains were expected to be high because of higher density of the limestone compared with the alluvial materials. In addition, magnetic anomalies over the architectural remains were expected to be positive because fire plays a great part in the transformation of haematite to maghemite by means of reduction and oxidization (Tite and Mullins, 1971;Gibson, 1986;Batayneh et al, 2001).…”