The Blake Geomagnetic Event as Inferred from Late Brunhes Ignimbrites in Southwest Japan and West Indonesia

Abstract

A reversed short polarity episode in the late Brunhes Epoch has been discovered in two dacitic welded tuffs located in Kagoshima, South Kyushu, Japan, and Siguragura, North Sumatra, Indonesia. Combined with the stratigraphic relations and both fission-track ages ranging 0.10-0.13m.y., each polarity episode is correlated with the Blake polarity event. If this is correct, then it is the first time that the Blake reversed event has been identified in igneous terrestrial rocks. Based on our results, along with the recently published, worldwide Blake episodes, it is strongly suggested that the hypothesis of a global geomagnetic reversal for the Blake event is more tenable than that of a local reversal model by DENHAM (1976).