Paleomagnetic results from Early Eocene intrusions, north‐central Montana: Implications for North American apparent polar‐wandering

Paleomagnetic poles have been determined from two Early Eocene igneous centers located in the north‐central Montana alkalic province. The mean paleomagnetic pole for the Highwood Mountains lies at 81.2°N, 167.3°E (N = 29; α95 = 7.1; k = 15.4) while the corresponding pole for the Bearpaw Mountains is located at 80.5°N, 198.4°E (N = 18; α95 = 5.8; k = 37.0). Combining these results with studies on Eocene rocks from Wyoming, gives a reference pole located at 81.7°N, 171.2°E with a circle of 95% confidence of 4.4°. This data, when compared to other early Tertiary results, the Cretaceous stillstand poles and the well grouped mid‐Tertiary poles from the continental interior, suggest that for the period 120 to 15 m.y.B.P. apparent polar‐wandering for North America occurred as a succession of rapid shifts of the geomagnetic pole separated by periods of stillstand.