Extension of the Middle Miocene Kleifakot geomagnetic instability event in Ísafjörður, Northwest Iceland

Abstract

— Detailed records of past geomagnetic polarity transitions and excursions are seldom found in extrusive volcanics. One type of such events seems to involve very irregular variations of the magnetic field direction. Several examples of that type have been discovered in paleomagnetic surveys on the Neogene lava pile of Iceland. Lava sequences spanning the most notable event are accessible in the two tributary fjords Mjóifjörður and Ísafjörður south of Ísafjarðardjúp, Northwest Iceland. Paleofield direction results from about 80 sampling sites in these sequences have been described in previous publications. The present paper adds 20 sampled sites in Ísafjörður, extending the area where parts of this „Kleifakot instability event“ of the geomagnetic field are recorded, to 5–6 kilometers along the fjord. Intermediate paleofield directions in the collection often agree closely with each other in correlated strata, even more than 4 kilometers apart. Events like this can provide valuable correlation tools for future stratigraphic mapping and various studies on volcanological features in the relatively uncharted region around Ísafjarðardjúp and beyond. Globally, recognition of the exis-tence of such events will aid in the interpretation of results in other kinds of paleomagnetic studies. The role of geomagnetic paleo-intensity determinations is discussed briefly in this context.