Dating Geomagnetic Polarity Zones

Abstract

INDEPENDENTLY McDougall and Tarling¹ and Cox, Doell and Dalrymple² recently published results from Hawaii and the Sierra Nevada, respectively, on magnetic polarities and the age of volcanic rocks. The polarities determined on rocks from these two regions were made using standard palæomagnetic techniques including magnetic cleaning. There was some disagreement among the results published in these two papers; but in view of errors in geological correlation made by Cox et al.² and later corrected³, it is desirable to clarify the present position, for the two sets of data are now found to be in good agreement. The aim of this comparison is to attempt to establish whether or not rocks with normal and reversed polarities in these two regions occur in the same time sequence. If rocks of the same age have the same polarity everywhere then the hypothesis that the exactly opposed polarities found in rocks are the result of reversals of the Earth's magnetic field is strongly supported. Should this be the case then the times at which field reversal occurred in the geological past may be estimated, and further the stratigraphic sequence of polarities established in one locality will provide a valuable means of geological correlation with other localities.