Project III.1: Dating the Late Cretaceous: pushing orbital tuning to its limits (Sietske Batenburg supervised by Mario Sprovieri / Andy Gale)

Objective: The aim of the project is to establish a high-resolution cyclostratigraphic reconstruction for the Late Cretaceous (Cenomanian-Maastrichtian) based on multi-proxy - lithological and geochemical - datasets collected from selected land-based marine sedimentary successions in Europe. In essence, once the stable long-term 405-kyr eccentricity and the 21-kyr precessional cycle are recognized in the lithological records and related datasets, it will be possible to extend the astronomical-tuned time scale from the K/T boundary to the base of the Cenomanian. The precision of this timescale will be independently verified through integrated biostratigraphical and carbon isotope correlations to marine successions from the Western Interior Basin in the USA; the latter successions contain bentonites for which new, high precision and accurate 40Ar/39Ar and U-Pb dates will be obtained (projects III.2 and III.3). Special attention will in addition be paid to a better understanding of the processes which controlled the ocean-climate response to the astronomical forcing during this classic "greenhouse" interval. This part will focus in particular on the phase relations between astronomical climate forcing and sedimentary response.

Background: The application of accepted and rigorously tested methods for a direct tuning of cyclic sedimentary records to astronomical target curves already reached a mature stage for most of the Neogene. On the other hand, only a limited number of relevant and methodologically reliable examples of cyclostratigraphic case studies are available for the Cretaceous. Age models that came out of these studies generally remain restricted to "floating" astrochronologies for the studied time-slices (e.g., Fiet et al., 2006; Sprovieri et al., 2006; Gale et al., 1999). This restriction is partly due to the lack of a reliable astronomical solution for this older part of the geological record at that time. In addition, a rather well-defined, albeit not definitive, paleoceanographic reconstruction is available for the Neogene to substantiate cyclostratigraphic interpretations and conceptually assess the Earth's ocean-climate response to external forcing. Such an adequate model is lacking for the Cretaceous, and the available information is limited and of regional importance only.

Research strategy and methodology: Lithological, sedimentological, faunal, isotopic and geo-chemical (major, minor and trace element assessment) analyses will be carried out on high-resolution samples from a selected number of high-quality cyclic marine successions for which an integrated magnetobiostratigraphy is already available. In particular, the composite record of the Umbria-Marche region in central Italy (Bottaccione, Bosso and Contessa sections) and records from SE France (Mont Risou section) and southern Engeland (Eastbourne section) will be investigated cyclostratigraphically in detail down to the scale of the precession cyclicity. Multi-proxy data (SEM and sedimentological analysis, isotope and geochemical analysis, etc.) will be used to determine in a semi-quantitative way the role of diagenesis in masking original signals, both in the proxy datasets and in the hierarchical organization of the sedimentary cycle patterns. Time series analysis (linear and non-linear spectral analysis, wavelet analysis, multi-taper spectral analysis, filtering techniques etc.) will be implemented to: i) identify and characterise the frequency structure of the datasets and ii) statistically validate the reliability of the cyclostratigraphic reconstructions. We will closely work together with the geochronologists of tasks III.2 and III.3 to obtain high-quality radio-isotopic dates necessary to verify and constrain the orbital tuning.

Feasibility: Recent papers (e.g., Gale et al, 1999; Fiet et al., 2006; Sprovieri et al., 2006) have demonstrated the potential of applying cyclostratigraphic methods to obtain reliable "floating" astrochronologies for different parts of the Cretaceous. The apparent excellent cyclic sedimentary records of the selected land-based marine successions in combination with the planned integrated multi-proxy and geochronological approach should ensure the construction of an astronomical calibrated time scale for the Late Cretaceous.

Innovative aspects and relevance: The project will result in a stable Late Cretaceous Time Scale with an unprecedented resolution, accuracy and precision.

Link with other projects: The project is directly linked to projects III.2 and III.3 which will provide the important independent validation of the orbital tuning through precise 40Ar/39Ar and U/Pb radio-isotopic age determinations combined with high-resolution integrated stratigraphic correlations.