Extended Data Fig. 4: MBT record and MIS 19.

Comparison of magnetostratigraphic (VGP) data across the MBT in Members OH4 and GH-CCC of Thomas Quarry I and in North Atlantic IODP deep-sea cores²⁴, correlated to the δ¹⁸O [‰] stack of 8 centred on Marine Isotope Stage (MIS) 19. Considering that the MBT (773 ± 4 ka) occurs during MIS 19c to MIS 18e²⁴ and that the sea-level transgression of MIS20/MIS19 began at ~795 ka²⁶, we interpreted the intertidal biocalcarenites of OH4-SU6 and the littoral sands of OH4-SU5 as part of this transgressive phase culminating whit a maximum flooding surface corresponding to the top of OH4-SU5. The following continental deposits of GH-CCC-SU4-3 are interpreted as the ensuing regressive phase associated to the MIS 19 high-stand beginning approximately at 780 ka. The transition between marine and continental sedimentation is gradual and substantially in stratigraphic continuity, implying a continuous and high-resolution recording of the MBT that is characterized by VGP swings between stable reverse (Matuyama) and stable normal (Brunhes) polarity. According to this interpretation, we attribute the thin normal magnetic polarity interval recorded in OH4-SU5 to the VGP variability of the MBT and exclude an attribution to the MB precursor dated to 794 ka²³ as this geomagnetic event occurred during MIS 20 and may have been recorded at or below the base of the sampled section.