S. Batenburg

ABSTRACT A refined astronomical tuning of the upper Albian-lower Campanian record is proposed from the Tethyan pelagic sedimentary sequence of the Bottaccione reference section (Umbria-Marche Basin, central Italy). Long-term eccentricity cycles filtered from a new high-resolution bulk sample δ13C signal were tuned to the highly stable 405 kyr cycles of the insolation target curve. Application of integrated methodologies of non-stationary/non-linear signals analysis (Intrinsic Mode Functions, WWZ Wavelet, non-linear filtering techniques, etc.) provided reliable numerical tools to explore the highly complex ~23 Myr long record. Exploration of the hierarchical pattern organization of lithology in selected parts of the sedimentary record provided an important constrain for the tuning strategy. The proposed orbital tuning provides a new and accurate age model for dating biostratigraphic, magnetic and carbon isotope events. Moreover, the exploration of long-term cycles (~1.2 to ~7.1 Myr) in the δ13C signal throughout the entire record offers an unprecedented chance to investigate processes associated to global carbon cycle dynamics and response to orbital forcing, biogeochemical cycles and sea level changes. Long-term eccentricity cycles of ~2.5 Myr beat the ~23 Myr long record although a direct control of this long-term eccentricity component on the deposition of sediments identified throughout the succession and coeval to the Bonarelli and mid-Cenomanian anoxic events can be unequivocally excluded. During the Turonian-Coniacian stratigraphic intervals, cycles of 1.2 Myr primarily modulate the δ13C curve , fuelling the debate on the potential role of glacio-eustacy on the carbon cycle during short-intervals of this super-greenhouse period. Finally, cycles of ~7.1, 4.5 and 3.2 Myr modulate the entire δ13C record and represent primary very long-term oscillation modes of Earth's climate-ocean system. Although an ultimate driver of these long-term periodicities is lacking we speculate that the 4.5 and 2.5 Myr cycles documented in the Late Cretaceous represent homologues of the present eccentricity grand cycles evolved by chaotic behaviour of solar planets during the Mesozoic. They could represent appropriate system low-frequency means for geological correlation and robust constraints on the orbital evolution of the Solar System.

The rhythmically bedded limestone–marl alternations in the coastal cliffs of Sopelana and Zumaia in the Basque country, northern Spain, permit testing and refining of existing Maastrichtian chronologies (latest Cretaceous). The recently established astronomical time scale for the late Maastrichtian at Zumaia is extended into C31n with the integrated stratigraphy of the Sopelana section. The cyclic alternations of hemipelagic limestones and marls at Sopelana show a strong influence of eccentricity-modulated precession. Together, the Zumaia and Sopelana sections span almost the entire Maastrichtian, and encompass thirteen 405 kyr cycles spanning a total duration of 5.3 myr. From the Cretaceous–Paleogene (K–Pg) boundary  downwards, 405 kyr minima in the lithological, magnetic susceptibility and reflectance data records are tuned to successive 405 kyr minima in the new La2011 eccentricity solution. Assuming a K–Pg boundary age of 65.97 Ma, we present orbitally tuned ages of biostratigraphic and magnetostratigraphic events. Whereas the bases of Chrons C29r and C30n were reliably established at Zumaia and are in good agreement with previous
studies, new data from Sopelana provide a refinement of the basal age of Chron C31r. Additional planktonic foraminifera and calcareous nannoplankton data from Zumaia, and new calcareous nannoplankton data from Sopelana, allow for worldwide correlation of the cyclostratigraphy of the Basque country.