In Search of the Bartonian (Middle Eocene) GSSP (II): Preliminary Results from the Oyambre Section (Northern Spain)

The Global Stratotype Section and Point (GSSP) for the base of the Bartonian (middle Eocene) stage is as yet undefined. Here, we assess the GSSP potential of the La Acebosa Formation exposed on the eastern side of the Cape of Oyambre (San Vicente de la Barquera, province of Cantabria, northern Spain). Sedimentological and benthic foraminiferal data indicate that the La Acebosa Formation represents a bathyal environment related to a deepening, eastward-facing slope. Preliminary planktic foraminiferal and calcareous nannofossil results show that the upper part of the section corresponds to zones E11 and CP14a, respectively, and thus could include the Lutetian-Bartonian boundary. Although the quality of demagnetization is quite poor, preliminary magnetostratigraphic data suggest that Chron C19n, which is most likely to define the Bartonian GSSP, could be recorded in the upper part of the La Acebosa Formation. A denser magnetostratigraphic and biostratigraphic sampling is required in the upper part of this unit in order to accurately identify Chron C19n and to establish the sequence of events across the Lutetian-Bartonian transition.