Milankovitch cyclicity within the middle Eocene deep-marine Guaso System, Ainsa Basin, Spanish Pyrenees

The Guaso System is the youngest deep-marine stratigraphic component in the middle Eocene deep-marine Ainsa Basin. In common with the older systems in the Ainsa Basin, it was mainly fed from the east/southeast by a range of sediment gravity-flow processes, including turbidity currents, debris flows and suspended-sediment river-derived plumes (e.g., hyperpycnal flows). A study of the Guaso System interfan sediments provides a 44m long geochemical stratigraphic-series, constructed from spectral gamma-ray (K, U and Th content) and bulk sediment geochemical data (CaCO3, TOC, δ18O and δ13C). Spectral and Average Spectral Misfit analyses of these data identify obliquity and precession orbital modes as present with respective periods of approximately ~10 and ~6m. These cycles are interpreted as reflecting carbonate dilution cycles linked to variation in siliciclastic sediment input into the Ainsa Basin. The presence of such orbitally induced carbonate dilution cycles is consistent with the identification of orbitally forced waxing and waning of coarse-grained sediment supply within the coeval up-system sediment supply system in the fluvio-deltaic Montanyana Group of the Tremp-Graus Basin. The presence of orbitally controlled sediment input to basin during interfan marlstone accumulation supplements to the growing body of evidence for the orbital control of sedimentation within the Ainsa Basin.