Paleomagnetism and geochronology of the Pliocene-Pleistocene lavas in Iceland

Abstract

Potassium-argon dates are reported on five basalt samples from the Pliocene-Pleistocene sequence of lavas in the Jökuldalur area, northeastern Iceland. These dates confirm the correlations previously made with the geological time scale by means of paleomagnetic stratigraphy. The R1 and N2 polarity epochs are shown to be equivalent to the Matuyama reversed and Gauss normal polarity epochs respectively. Within the N2 (Gauss) normal epoch up to three successive lava flows occur which are reversely magnetized. Dating of a normally magnetized basalt immediately below these reversed lavas gives a result of 3.10 ± 0.10 m.y., and confirms the reality of the Mammoth reversed event, first recognized in California. Two intercalations of normally magnetized lavas occur in the R1 (Matuyama) reversed epoch. The older of the normal flows may represent the Olduvai event; the younger normal polarity flow has been dated at 1.60 ± 0.05) m.y., and possibility indicates the presence of yet another normal event in the Matuyama reversed epoch. We propose the name Gilsá for this possible additional event.

Immediately above the basalt dated at 3.10 ± 0.10 m.y., occurs a tillite, which suggests that regional glaciation commenced in Iceland at about this time. Hence, the base of the Pleistocene may be as old as 3 m.y.