Archaeomagnetic paleointensity in the American Southwest during the past 2000 years

Details Archaeomagnetic paleointensity in the American Southwest during the past 2000 years Archaeomagnetic paleointensity in the American Southwest during the past 2000 years

Jul 1989

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1989pepi...56....1s&link_type=abstract

Physics of the Earth and Planetary Interiors, Volume 56, Issue 1-2, p. 1-17.

Physics

14

Scientific paper

An archaeomagnetic paleointensity study was carried out on pottery samples from the Hohokam, Anasazi, and Mogollon cultures of the American Southwest. The Thellier-Thellier paleointensity experiment was used on 187 specimens from 77 different sherds derived from 23 archaeological sites. Interpretations were made for 127 specimens from 54 sherds, about a two-thirds success rate. The median value for the quality factor was 12. The results were corrected for magnetic anisotropy owing to a fabric in the pottery, using an easy-plane model of magnetization. The anisotropy of the hard axis relative to the easy plane of magnetization averaged 31%. The correction factor for the paleointensity was typically 5.4%, and systematically increased the paleointensities because the laboratory heatings were applied within the easy plane. The sample-average paleointensities were compiled along with other data from North America. The Hohokam data were kept as a separate set because of uncertainties concerning the Hohokam chronology. Curves of the virtual axial dipole moment (VADM) variation for the Hohokam and non-Hohokam data sets were derived using a moving-window smoothing technique. The Hohokam and non-Hohokam curves show good agreement, regardless of which Hohokam chronology is used. Relative paleointensity records from North American lake sediments are also congruent with the archaeointensity results. Despite the scatter in the archaeomagnetic data, the correlation of these records suggests that the secular variation pattern is being recovered. The field strength at 300 BC is 30-40% higher than at present; a low from 250 to 1250 AD is 10-15% weaker than at present; and a peak at 1500 AD is about 30% higher than at present. The low from 250 to 1250 AD in comparison with global paleointensity compilations suggests a substantial non-dipole field in North America at that time. The rate of change of the archaeomagnetic VADM is similar to rates observed today.
Present address: Department of Geology, Franklin and Marshall College, Lancaster, PA 17604-3003, U.S.A.

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