Palaeomagnetism of Atlantic Islands: Fernando Noroñha

Abstract

BECAUSE of their role in testing the crustal spreading hypothesis¹ the ages of Atlantic islands have assumed a prime importance². Conventional geological methods are not usually applicable to studies of oceanic islands, because of the general lack of stratigraphically useful fossils and the dominantly volcanic environment. Palaeomagnetic methods, as pioneered by Einarsson³, however, can provide valuable stratigraphic indices in volcanic regions. In addition, if defined from a time span sufficient to average out secular variation⁴, palaeomagnetic poles can provide age estimates, because with increasing age they have occupied positions at increasing angular distances from the present geographic pole. Palaeomagnetic surveys are forming the bases of diverse studies of Atlantic islands. This is the third in a series of reports^5,6, in which the palaeomagnetic poles resulting from these surveys are reported.