Magneto-biostratigraphic succession of the Jaca Basin (Southern Pyrenees, Spain): insights on the Middle Eocene Climatic Optimum.

Magnetostratigraphy is a basic method to provide age constrains when trying to identify paleonvirmental changes in sedimentary successions. This is particularly important in the case of the Middle Eocene Climatic Optimum (MECO), which is a climatic perturbation not exactly coincident with a biostratigraphic boundary and having a peak Ca 40.2 Ma. We introduce the Jaca basin record (Southern Pyrenees) where expanded sedimentary successions record several Eocene climatic episodes. Combined magneto-biostratigraphic dating of these successions is carried out in the Hecho Group (deep clastic systems) and in its vertical successions to the Sabiñánigo and Belsué-Atarés deltaic systems.

New magnetostratigraphic data permit the identification of paleopolarities on the basis of stable demagnetization results from the marls of the deltaic successions. Counting of 32 species of calcareous nanoplankton for biostratigraphic purposes has permitted to identify several biozones throughout the basin. With respect to the MECO, the CNE14/15 biozones boundary has been clearly identified, which is close to c18r/c18n reversal.

A multiproxy study is carried out including mineralogical, elemental and isotopic data from X-ray diffraction, X-ray fluorescence and bulk rock C/O stable isotopes, with the aim to achieve a paleoenvironmental proxy permitting the identification of the MECO.  Ultimately, the integrated chronostratigraphic and multiproxy characterization of the studied sections will permit to understand how deltaic systems reacted the MECO climatic event.