Objects under this category are not only easier to find than most other objects at archaeological sites, but in certain cases where their kiln baked position with respect to the vertical is known ,they can also be used to estimate the age of the object. This can be determined by measuring the inclination of the remanent magnetization which occurred at the time it was baked. The magnetic inclination can be compared with the history of the variation of the earth’s magnetic inclination known through historical records and other fire-baked clay objects already dated by other methods.
MAGNETISATION AND SUSCEPTIBILTY OF SOILS
Magnetic susceptibility of soils is general related to the susceptibility of the rocks from which they were obtained. Therefore soils from volcanic or other igneous rocks have a higher susceptibility than soils weathered from sandstone, limestone or shale. Magnetite being one of the most resistant minerals appears to be present in the soils in higher proportion than other more soluble minerals. Subsequently, organic action particularly in high-humus soils is thought to be responsible for the formation of the magnetic mineral, maghemite, from other non-magnetic forms of iron oxide a phenomenon of importance in mapping features associated with habitation. Soils may have higher susceptibility than that indicated by parent rocks. Surface magnetite is a source of magnetic noise in precision magnetic surveys performed very close to the surface of the ground elite.
REMANENT MAGNETISATION OF SOILS
This remanent magnetization is mostly common in the upper layers of soil and if disturbed by cultivating, digging graves, foot or animal traffic or by other physical disruption of the integrity of the soil, is destroyed creating ...
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...netometer sensor and the center of the void is much greater than the diameter of the void. This is due to the fact that in order to detect the void, the soil or rock must have an appreciable magnetization i.e. the higher the contrast the larger the anomaly.
Large magnetization are associated with non-uniform or inhomogeneous magnetization which is a significant source of magnetic noise obscuring the subtle anomaly signatures of the void.as shown if fig 48 below.
Fig 48.Typical magnetic anomalies of common archaeological features.
Works Cited
APPLICATIONS MANUAL FOR PORTABLE MAGNETOMETERS
By S.BREINER
Geometrics,395 Java Drive
Sunnyvale,California 94086
U.S.A.
SOLID STATE PHYSICS
By S.O.PILAI.
Adapted from ES304 – Geophysical Prospecting, Earth Science Department
University of Melbourne, Australia.
By Dr.Kamar Shah Ariffin.