Timing of the Brunhes-Matuyama transition constrained by U-series disequilibrium

Bassam Ghaleb (1) , Christophe Falguères (2) , Julie Carlut (3) , Jean-Pierre Pozzi (4, 2) , Geoffroy Mahieux (5) , Larbi Boudad (6) , Louis Rousseau (2)

1 GEOTOP - Centre de recherche sur la dynamique du système Terre
2 HNHP - Histoire naturelle de l'Homme préhistorique
3 IPGP - Institut de Physique du Globe de Paris
4 LGENS - Laboratoire de géologie de l'ENS
5 B2R - Bassins - Réservoirs - Ressources - U2R UPJV-UNIL 7511
6 UMI - جامعة مولاي إسماعيل = Université Moulay Ismaïl

U-series disequilibrium measurements carried out on thermogenic travertine samples from a 12.6 m-long core and a 10 m-thick section from southeastern Morocco yielded finite ages ranging from 500 ka to the present-day, as well as two clusters determined to be older than 500 ka. The calculation of initial 234 U/ 238 U activity ratios in all samples younger than 500 ka shows high, reasonably constant values, with an average of 5.172 ± 0.520 (one standard deviation). Assuming that this value prevailed for periods older than 500 ka, we derived ages of up to approximately 1.2 Ma using the initial 234 U excess decay. Our results indicate that the two older clusters have ages of 776 ± 14 ka for samples from between 8 and 10.1 m and 1173 ± 22 ka for deeper samples respectively. The palaeomagnetic record of the core shows normal polarity inclinations from the surface to around 9 m followed by reverse polarity inclination and antipodal declinations. The inversion is attributed to the Brunhes-Matuyama transition. 234 U excess ages for the interval corresponding to the part of the core where the polarity inversion occurred are in the range of 735 ± 51 to 794 ± 54 ka, with an arithmetic mean value of 776 ± 14 ka for the B-M transition. This age is in good agreement with that determined previously using other dating methods.

Domaines: Géophysique [physics.geo-ph]

Bassam Ghaleb, Christophe Falguères, Julie Carlut, Jean-Pierre Pozzi, Geoffroy Mahieux, et al.. Timing of the Brunhes-Matuyama transition constrained by U-series disequilibrium. Scientific Reports, 2019, 9, pp.6039. ⟨10.1038/s41598-019-42567-2⟩. ⟨insu-02178712⟩