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New age for the Skalamælifell excursion and identification of a global geomagnetic event in the late Brunhes chron

, : New age for the Skalamælifell excursion and identification of a global geomagnetic event in the late Brunhes chron.

Sixteen lava flows sampled from isolated hills, including Sk lam lifell hill, on the Reykjanes Peninsula in southwest Iceland record excursional geomagnetic field directions that correspond to virtual geomagnetic poles (VGPs) grouped at 12 S, 25 E in the eastern Pacific Ocean. The VGPs are similar to those obtained in earlier studies of these lavas, for which the name Sk lam lifell excursion was previously assigned. Based on unspiked K Ar dating of nine samples from six hills, it has been accepted for more than two decades that the transitionally magnetized lavas reflect the 41 ka Laschamp excursion. However, nine newAr/Ar incremental heating experiments on four of the transitionally-magnetized lavas give an age of 91 13 ka. Moreover,U Th isochrons determined for two of these lava flows yield a weighted mean age of 96 1 ka (2?). The weighted mean of theAr/Ar andU Th ages is 94.1 7.8 ka (2?), which is more than twice as old as the K Ar data imply. We conclude that the Sk lam lifell excursion is not synchronous with the Laschamp excursion. Rather, the Sk lam lifell excursion likely corresponds to the post-Blake excursion at 94 ka, which coincides with a globally observed low in paleointensity. These findings highlight the potential shortcomings of K Ar dating of young (< 1 ka), low-K basalts, and reinforce the need for multiple independent chronometers when determining ages for geologic events throughout Earth's history.The focus of the study is on the age of the Sk lam lifell excursion. The new age of the excursion is twice as old as published K Ar ages. We point out some pitfalls in using the K Ar technique on young, low-K lavas. We highlight that the 94 ka Sk lam lifell excursion is a global phenomenon..


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