Paleomagnetism and geochronology of early Middle Pleistocene depositional sequences near Rome: comparison with the deep-sea δ18O record

A sequence-stratigraphic analysis was carried out on clastic coastal deposits (Ponte Galeria Formation – PGF) of the Tiber River delta, cropping out to the southwest of Rome, in order to correlate these sequences to Pleistocene eustasy. Tectonic subsidence affected sedimentation, but is distinguished from the glacio-eustatic signal, showing that the PGF consists of four depositional sequences that correlate to two fourth-order cycles. A paleomagnetic investigation of clay horizons deposited before and after the Brunhes–Matuyama reversal, combined with 40Ar/39Ar ages from a tuff horizon within the PGF, constrain the timing of the relative sea-level changes and allow us to tie it to the astronomically calibrated deep-sea δ18O record. The Brunhes–Matuyama boundary in the PGF postdates a set of highstand systems tract sediments, suggesting that the reversal occurs late in δ18O stage 19. This position is consistent with the recent study of deep-sea cores by Bassinot et al. [Earth Planet. Sci. Lett. 126 (1994) 91–108]. The assumption of a common continental stage marking the start of the Middle Pleistocene (δ18O stage 22) in the Mediterranean region is not supported by the Tiber River sections which, in our interpretation, begin at stage 20.