The secular variation of the geomagnetic field in Egypt in the last 5000 years

Hussain, Aftab

doi:10.1007/bf00878614

Cited by 21 publications

(29 citation statements)

References 5 publications

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“…Previous paleointensity studies in Egypt were carried out by Athavale (1969), Games (1980), Hussain (1983Hussain ( , 1987, Aitken et al (1984), Walton (1986), Odah (1993), and Odah et al (1995). Odah et al (1995) have constructed a preliminary secular variation curve for the geomagnetic field in Egypt for the time between 4000 BC and 2000 AD.…”

Section: Introductionmentioning

confidence: 99%

Improvement of the secular variation curve of the geomagnetic field in Egypt during the last 6000 years

Odah

2014

Earth Planet Sp

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A total of 115 ceramic specimens out of 41 samples from 9 archeological sites in Giza, Fayoum, Benisuef, El Minia, Malawy, and Sohag were collected. They represent 14 well-determined ages covering the last 6000 years. Rock magnetic properties such as Curie temperature and hysteresis loops have been measured for these samples to identify the magnetic carrier; it is found to be fine-grained magnetite. All specimens were investigated using the classic Thellier double heating technique (Thellier and Thellier, 1959) and the modification after Odah et al. (1995) to obtain the paleointensity data. These paleointensities and the previous results of Odah et al. (1995) were used to improve the secular variation curve of the geomagnetic field in Egypt for the last 6000 years. This curve shows a maximum of 72.8 μT at about 250 AD and a minimum of 33 μT at about 3500 BC. It also shows a general decrease of the magnetic moment during the last 2000 years.

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Section: Introductionmentioning

confidence: 99%

Improvement of the secular variation curve of the geomagnetic field in Egypt during the last 6000 years

Odah

2014

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“…It was shown that the magnetic anisotropy could produce errors of up to 25% (e.g. Hussain, 1987). From the present work it was shown that this effect can be even greater and in extreme cases, the differences between the results from a collection of one age can reach as much as 58%.…”

Section: Discussionmentioning

confidence: 70%

“…A decrease in the magnetite fraction and some sorting of the grain sizes occurs along the 1300 km of the Egyptian Nile. The intensity of magnetization of the brick samples from Aswan is much higher than that from northern Egypt at Monshaät Abu Omar, El Dakahlia (Hussain, 1987). These fine grains in the archaeological ceramic and bricks were homogeneously oxidized or reduced when they were heated during manufacture.…”

Section: Discussionmentioning

confidence: 88%

“…Chemical alteration during the Thellier double heating processes, magnetic anisotropy, and the difference between the rates of cooling when acquiring the TRM in ancient times and under laboratory conditions were found to affect the experimentally determined palaeointensities (e.g. Coe, 1967;Rogers et al, 1979;Fox and Aitken, 1980;Kono and Tanaka, 1984;Kono, 1987;Hussain, 1987;Aitken et al, 1989;Yang et al, 1993).…”

Section: Introductionmentioning

confidence: 99%

“…The pots are produced on a rotating disc. This results in magnetic anisotropy, with susceptibility largest in direction parallel to the wall of the pot and smallest perpendicular to it (Rogers et al, 1979;Hussain, 1987). Formed pots were left to dry in air and then fired at temperatures much higher than the Curie temperature for several days and left to cool in the ancient geomagnetic field.…”

Section: Introductionmentioning

confidence: 99%

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Effect of magnetic anisotropy on the experimentally determined palaeointensity of the geomagnetic field

et al. 2014

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Rock magnetic properties of the Nile mud are reported. They indicate that the carrier of magnetization in the Nile mud is predominantly magnetite. Fourty air-dried ceramic samples made of Nile mud were manufactured to ceramics by stepwise heating to 700• C at various field intensities between 0.03 mT and 0.09 mT and with various angles θ between the laboratory field (F L ) direction and the ceramics. The partial (pTRM) and the total thermoremanent magnetization (TRM) increase linearly as the magnetic field (F L ) increases. The rate of increase of the pTRM with both F L and temperature T depends on θ , so that it decreases by 25% as θ increases from 0• to 90• . In extreme cases, the effect of the magnetic anisotropy results in overestimating the determined palaeointensity by 33% and underestimating it by 25% from the correct value. The direction of TRM is the same as that of the ambient magnetic field independent of the anisotropy. Applying the laboratory field in the direction of the stable natural remanent magnetization during a Thellier-type experiment results in accurate determination of the palaeointensity.

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