Age and magnetism of lavas in Jokuldalur area, Eastern Iceland: Gilsa event revisited

We present results of paleomagnetic measurements and K-Ar age determination s of 38 lava flows collected in five separate sections in the Jokuldalur ar ea of Eastern Iceland, including one section previously studied by Watkins et al. [Watkins, N.D., Kristjansson, L., McDougall, L, 1975. A detailed pal eomagnetic survey of the type location for the Gilsa geomagnetic polarity e vent. Earth Planet. Sci. Lett. 27, 436-444]. These sites are close to the t ype locality of the normal "Gilsa event" in the Matuyama chron first identi fied by McDougall and Wensink [McDougall, I., Wensink, H., 1966. Paleomagne tism and geochronology of the Pliocene-Pleistocene lavas in Iceland. Earth Planet. Sci. Lett. 1, 232-236]. Using new experimental results as well as f ield observations, we could correlate the sequence of lava flows in the Jok uldalur area spanning the time interval between 1.8 and 0.5 Ma. The magneti c polarities and ages obtained in this study are quite consistent with the standard time scale for Brunhes-Matuyama ages given by Cande and Kent [Cand e, 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 Gilsa event needs to be added. Existence of Olduvai age lavas under Gilsa was inferred but n ot certain. Our results are fairly in good agreement with the former studie s by Wensink [Wensink, H., 1964a. Secular variation of Earth magnetism in P lio-Pleistocene basalts of eastern Iceland. Geol. Mijnbouw 43, 403-413; Wen sink, H., 1964b. Paleomagnetic stratigraphy of younger basalts and intercal ated Plio-Pleistocene tillites in Iceland. Geol. Rund. 54, 364-384] and Wat kins et al. [Watkins, N.D., Kristjansson, L., McDougall, I., 1975. A detail ed paleomagnetic survey of the type location for the Gilsa geomagnetic pola rity event. Earth Planet. Sci. Lett. 27, 436-444], but the assignment to th e polarity zones is different because of the newly obtained K-Ar ages. Base d on the present study, we propose that the Gilsa event is a short normal s ubchron in the Matuyama chron distinct from and above the more well-establi shed Oldvai subchron. (C) 1999 Elsevier Science B.V. All rights reserved.