Astronomically Controlled Cycles of Mid-Cretaceous Anoxic Events

The Cretaceous pelagic sections of the Umbria – Marches region of Italy contain a remarkably long, continuous, and accessible record of cyclic lithologic variations that inspired some of the first and most important investigations of the astronomical influence on climate and sedimentation. The time period covered by these sections includes a series of oceanic anoxic events (OAEs), whose origin has been a matter of debate for decades. Several of these OAEs (1d, the Mid-Cenomanian Event, OAE2, and OAE3) occur within the ~ 10 Ma represented by the Scaglia Bianca through lower Scaglia Rossa Formations. We have undertaken a spectral analysis of the lithologic cycles from these formations in order to investigate the occurrence of these OAEs in the context of astronomical cycles. Throughout much of this section, the lithologic variations reflect oscillations in the biogenic silica, carbonate, and organic carbon contents that are interpreted here as oscillations of surface eutrophy and bottom water anoxia; briefer and less extreme versions of the OAEs. Spectral analysis of numerically coded lithologic alternations reveals a robust set of cycles whose periods are remarkably similar to the orbital cycles calculated by Laskar et al. (2004). Matching the stratigraphically preserved eccentricity signals to the theoretical eccentricity yields ages and durations of several of the OAEs. At least 2 of the OAEs coincide with protracted periods of unusually low insolation variation, owing to simultaneous nodes in the obliquity and eccentricity. From this perspective, the timing of many OAEs may be astronomically controlled. The possible stratigraphic recording of these simultaneous nodes of obliquity and eccentricity may also provide some insight into time periods of chaotic and resonant behavior in the orbits of the Earth and Mars.