Palaeomagnetism of Cretaceous Pacific Seamounts *

Summary. The palaeomagnetism of Cretaceous Pacific seamounts, as deduced from their magnetic anomalies, is reviewed. Results from 35 seamounts are reported here for the first time. Of these 35 results, 15 are of high enough quality to be useful. This has resulted in a considerable increase in the available information concerning the palaeomagnetism of the Pacific plate. Using only the most reliable results, we calculate a palaeomagnetic pole for the upper Cretaceous at 58° North, 350° East, with a 95 per cent cone of confidence of only 5°. This pole is considerably more accurate than the one previously reported and is farther to the west. The previously reported difference between the mean pole position from seamounts close to Japan and the mean pole position from seamounts close to Hawaii is not real, although one group of seamounts close to Japan gives an anomalous pole position. Several mechanisms have been suggested whereby errors might be introduced in the determinations of pole positions from seamounts. No error is introduced in the pole position because of the restricted extent of surveys and the consequent inaccuracy in the determination of the regional field. The demagnetization effect, which can produce differences between the observed direction of magnetization and the direction of the magnetizing field in an elongated body, is unimportant for seamounts. The new pole position is sufficiently accurate for use in many types of calculations in which it is desired to locate the Pacific plate with respect to the Earth's spin axis.