Magnetobiochronology of the Izaga section (South Pyrenean Foreland basin): Implications for defining the global boundary stratotype section and point (GSSP) of the Bartonian Stage and unravelling climate change across the Middle Eocene Climate Optimu

We present a new magnetobiostratigraphic study of the Izaga composite section (South Pyrenean foreland basin), performed to investigate the possibility of defining the Bartonian GSSP and to assess the yet unexplored sedimentary expression of the Middle Eocene Climate Optimum (MECO) in the deep palaeoenvironments of the basin. Our results indicate that the section spans from the uppermost part of Chron C19r to the uppermost part of C18n.2n, comprising calcareous nannofossil biozones CNE14 and CNE15. As found in most prospective sections studied previously, the occurrence of delayed magnetizations has prevented precise delineation of the marker of the Bartonian GSSP, the short lived Chron C19n, which reinforces the idea that an alternative biostratigraphic event might need to be chosen as the primary marker of the GSSP. In this regard, we propose the highest occurrence of Sphenolithus furcatolithoides B, whose persistent location close to the top of C19n has been corroborated at the Izaga composite section. If this datum accepted, the Izaga composite section can be regarded as one of the best prospective successions to host the Bartonian GSSP due to its expanded nature and superb outcrop conditions. Our results also reveal an increase in the input of reworked calcareous nannofossils and organic matter of continental origin concurring with a negative shift in the carbonate carbon and oxygen stable isotope record around the C19r/C18n.2n boundary, and hence demonstrate that the enhanced hydrological cycle induced by the MECO is manifested along a complete continental to deep marine transect along the South Pyrenean basin. • Izaga section spans from the uppermost C19r to the uppermost C18n.2n. • Slightly delayed remanences comprise the accurate record of Chron C19n. • Sphenolithus furcatolithoides B HO proposed as primary marker of the Bartonian GSSP. • Bartonian GSSP proposed to be placed at the Izaga composite section. • Imprint of the MECO identified along a continental to deep marine transect.