Age and magnetism of lavas in Jökuldalur area, Eastern Iceland: Gilsá event revisited

Abstract

We present results of paleomagnetic measurements and K–Ar age determinations of 38 lava flows collected in five separate sections in the Jökuldalur area of Eastern Iceland, including one section previously studied by Watkins et al. [Watkins, N.D., Kristjansson, L., McDougall, I., 1975. A detailed paleomagnetic survey of the type location for the Gilsá geomagnetic polarity event. Earth Planet. Sci. Lett. 27, 436–444]. These sites are close to the type locality of the normal “Gilsá event” in the Matuyama chron first identified by McDougall and Wensink [McDougall, I., Wensink, H., 1966. Paleomagnetism and geochronology of the Pliocene–Pleistocene lavas in Iceland. Earth Planet. Sci. Lett. 1, 232–236]. Using new experimental results as well as field observations, we could correlate the sequence of lava flows in the Jökuldalur area spanning the time interval between 1.8 and 0.5 Ma. The magnetic polarities and ages obtained in this study are quite consistent with the standard time scale for Brunhes–Matuyama ages given by Cande and Kent [Cande, S.C., Kent, D.V., 1995. Revised calibration of the geomagnetic polarity timescale for the Late Cretaceous and Cenozoic. J. Geophys. Res. 100, 6093–6095] based on marine magnetic anomalies, except that the Gilsá event needs to be added. Existence of Olduvai age lavas under Gilsá was inferred but not certain. Our results are fairly in good agreement with the former studies by Wensink [Wensink, H., 1964a. Secular variation of Earth magnetism in Plio–Pleistocene basalts of eastern Iceland. Geol. Mijnbouw 43, 403–413; Wensink, H., 1964b. Paleomagnetic stratigraphy of younger basalts and intercalated Plio–Pleistocene tillites in Iceland. Geol. Rund. 54, 364–384] and Watkins et al. [Watkins, N.D., Kristjansson, L., McDougall, I., 1975. A detailed paleomagnetic survey of the type location for the Gilsá geomagnetic polarity event. Earth Planet. Sci. Lett. 27, 436–444], but the assignment to the polarity zones is different because of the newly obtained K–Ar ages. Based on the present study, we propose that the Gilsá event is a short normal subchron in the Matuyama chron distinct from and above the more well-established Oldvai subchron.