The geomagnetic field magnitude variations in Peru during the last 2000 yr have been determined from archaeological ceramics collected by the Oxford and Liverpool Universities Archaeomagnetic Expedition of 1975. Shaw's method of palaeomagnitude determination was used in conjunction with thermoluminescence dating. An overall decrease in field magnitude was observed, but with clear maxima near ad 900 and 1400, and minima near ad 600 and 1100. Comparison with data from elsewhere would suggest that variations with submillennium periods are real but not contemporaneous over the globe. This underlines the importance of good absolute dating in archaeomagnetic studies and the cautious use of averaging and smoothing procedures.
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Gunn et al. (1980) studied this question.