Archeomagnetism of potsherds from Grand Banks, Ontario: a test of low paleointensities in Ontario around A.D. 1000

An archeomagnetic study was carried out on 24 pottery fragments from Grand Banks, southern Ontario. 14C dating on maize found in the same pit as the potsherds gives an age in the range A.D. 990–1160 (modal age A.D. 1030). Hysteresis measurements indicate that the natural remanent magnetization is carried by pseudosingle-domain magnetite grains. Paleointensity experiments were done on 63 samples using a Thellier-type double-heating method. Half of the samples were heated in helium and the other half in air. Hysteresis measurements on samples after heating to various temperatures reveal only slight mineralogical changes during heating steps. Thirty reliable results give a paleofield intensity of 42.0±7.4 μT, and a virtual axial dipole moment of 7.0±1.3×1022 Am2. This result is in agreement with the low virtual axial dipole moment values given by studies on material from Ontario compared to the values from the southwestern USA in the interval A.D. 900–1400.