Astronomical tuning of the Cenomanian Scaglia Bianca Formation at Furlo, Italy

The astronomical tuning of the upper Cenomanian rhythmic succession of marine limestones and black shales that prelude to the Bonarelli Level (= Oceanic Anoxic Event 2) in the classic Furlo section of central Italy was achieved using cyclostratigraphic analyses on environmentally controlled rock-magnetic properties and the CaCO3 content of the limestones. The astronomical tuning was based on the stable 405 kyr-long eccentricity cycle observed in the rock-magnetic record and correlated to the orbital solution of Laskar et al. (2004), and the phase relationship was established by the eccentricity-modulated precession signal observed in the CaCO3 record. According to our tuning, pre-Bonarelli black shales formed during eccentricity minima and reduced seasonality when reduced deep-water circulation (sea bottom ventilation) in a paleogeographically constricted Alpine Tethys–Central Atlantic Ocean promoted organic matter preservation and possibly a reduced carbonate dissolution resulting in a higher sedimentation rate. In compliance, the onset of the OAE2 at Furlo corresponds to the eccentricity minimum nominally placed at 93.92 Ma, with the full development of OAE2 persisting much longer than any black shale precursor across at least one long eccentricity maximum.