Chemostratigraphic correlation of Barremian and lower Aptian ammonite zones and magnetic reversals

Abstract.

Based on carbon-isotope stratigraphy we correlate the ammonite-dated Barremian reference section near Angles (SE France) with the magneto- and biostratigraphically dated succession at Cismon (northern Italy). The results confirm the previous correlation of the lower Barremian ammonite- and magnetostratigraphy by Channell et al. (1995) and show that the base of CM0 selected as the stage boundary between the Aptian and the Barremian coincides with the stage boundary defined by ammonite stratigraphy. The upper Barremian carbon-isotope record of the Cismon section displays two positive δ¹³C excursions, whereas the data from Angles show only one shift towards more enriched values. The absence of the second upper Barremian δ¹³C excursion at Angles indicates that up to 50% of the Barremian stage is missing in the selected reference section. The gap occurs most probably within the giraudi ammonite zone and is related to the 12d maximum flooding surface of Jacquin et al. (1998).