Late Cretaceous orbitally-paced carbon isotope stratigraphy from the Bottaccione Gorge (Italy)

Abstract

A refined astronomical tuning of the upper Albian−lower Campanian is proposed from the Bottaccione reference section (Gubbio, central Italy). Long-term eccentricity cycles filtered from a high-resolution δ13C record were tuned to the highly stable 405kyr cycles of the new La2010 astronomical solution for the Earth's orbital elements. The achieved orbital tuning provides a new precise, and accurate age model for dating biostratigraphic, magnetostratigraphic and carbon isotope events through a ~23Myr long record. Cycles of ~8.0, 4.7, 3.4 and ~2.4Myr modulate the entire δ13C record, thus extending their detection from the Cenozoic to ~100Ma and represent primary and stable long-term oscillation modes of Earth's climate–ocean system. Although an ultimate driver of these long-term periodicities is lacking, we speculate that specifically the periodicity at 4.7Myr, represents a homologue of the present eccentricity grand-cycles, evolved by the chaotic behaviour of solar system planets during the Mesozoic. The long-term periodicities potentially reflect an unexplored expression of the low-frequency response of the carbon cycle to global biogeochemical dynamics of major nutrients, particularly phosphorus, associated with modulation of inputs to the ocean in turn triggered by high-order marine transgressions and formation of highly productive shelf seas. This very long-term eccentricity control, modulated by periodic low-energy cycles, is suggested to play a crucial role in carbon cycling, controlling a chain of climate sensitive global biogeochemical processes on the Earth. Finally, these grand-cycles provide a potential tool for geological correlation and provide a robust constraint for accurate calculation of the orbital evolution of the Solar System.