Aptian Stage Astronomic Calibration in Poggio le Guaine Core (Cagli, Italy)

The Early Cretaceous Aptian stage, whose base coincides with the onset of the Cretaceous Normal Superchron, has also been considered as a geological interval of major, dramatic climate changes. Oceanic anoxic events (OAE) in this stage enabled the deposition of black shales worldwide, such as the Selli Level (OAE1a), as well as the Kilian, Jacob and Fallot levels. Also periodic changes in ocean floor redox conditions resulted in the deposition of intervening oceanic red beds (ORBs). Yet, the chronologic framework for the Aptian stage is still debatable, as there is no consensus on its lower age boundary despite well-preserved and continuous sedimentary records reported in literature. In such context, a core recently drilled at Poggio le Guaine (PLG; northern Apennines, central Italy) which comprises the ~ 36 m of the pelagic Maiolica and Marne a Fucoidi Formations represents an outstanding opportunity to investigate the Aptian sedimentation processes and related long-term climate forcing factors. In this work, we present a high-resolution age model for the Aptian stage based on cyclostratigraphy using the magnetic susceptibility (MS) and the anhysteretic remanent magnetization (ARM) datasets obtained form the continuous sampling of the PLG core. Preliminary results carried out from an astronomical calibration based on time-frequency and spectral analyses are strongly suggestive of Milankovitch-bands astronomical cycles at dm-scale - 0.5-0.8 m (short eccentricity), 0.2-0.3 m (obliquity) and 0.13-0.18 m (precession), which implies in a time interval of approximately 7.2 Myr between the Kilian and the top of the Selli level, in contrast with previously published models for the same time-period.