The age and duration of the Matuyama–Brunhes transition from new K–Ar data from La Palma (Canary Islands) and revisited 40Ar/ 39Ar ages

Abstract

Paleomagnetic investigations conducted on lava sequences from La Palma (Canary Islands) yielded several independent records of the Matuyama–Brunhes transition (MBT). Seven K–Ar ages of flows sampled across the MBT suggest a duration between 0 and 11 kyr, and provide a weighted mean age of 786±3 ka (analytical uncertainty only) for the transition. This value is significantly older than the previously admitted age of 779±2 ka, derived from volcanic or sedimentary sequences. When the 1% uncertainty on the calibration standard used in the present study is considered, our age for the transition recorded at La Palma becomes 786±8 ka. We have recalculated the 40Ar/ 39Ar determinations from the previous studies using recent revisited ages for 40Ar/ 39Ar standards. This yields a global dataset of 23 K–Ar and 40Ar/ 39Ar determinations. Our best estimate for the MBT age derived from this compilation is 789±2 ka (analytical error), or 789±8 ka (total error). Within this 8 kyr uncertainty, which could be considered as a minimum estimate, this age remains compatible with recent determinations made by the astronomical time scale. However, the present study suggests that better control of the lock-in depth, as well as better quantification of uncertainties involved in the tuning of δ 18O records to orbital forcing models, are needed to improve further the astronomical polarity time scale derived from sedimentary records. In addition, absolute dating by K–Ar and 40Ar/ 39Ar will gain in accuracy when uncertainty determinations on standards will be significantly improved.