Orbital tuning of a lower Cretaceous composite record (Maiolica Formation, central Italy)

Abstract

A high‐resolution pelagic bulk carbonate stable isotope record from a central Tethyan lower Cretaceous composite section is presented. Three well‐exposed sedimentary sequences (Chiaserna Monte Acuto, Bosso, and Gorgo a Cerbara sections, central Italy) cropping out throughout the Maiolica Formation were correlated by a detailed magnetostratigraphy, lithostratigraphy, and calcareous plankton biostratigraphy in order to reconstruct a continuous composite record from the middle Berriasian to the lower Aptian. The integrated stratigraphy of the three sequences provided an accurate time framework for the new high‐resolution C isotope curve which is presented in this study. The composite δ13C signal, recorded in the depth domain, was analyzed by combined Lomb‐Scargle periodogram and weighted wavelet Z transform (WWZ) – weighted wavelet amplitudes (WWA) Foster wavelet spectral methodologies, both appropriate for unevenly sampled curves. These tools allowed us to unravel the main frequencies modulating the record and their hypothetical shift in depth, respectively. The long‐term, ∼400,000 and ∼2,400,000 years, eccentricity cycles were consistently recorded throughout all the composite record. Once band‐pass filtered in these two periodicity bands and compared to the lithologic pattern cycles identified throughout the composite sequence, the δ13C signal was used as a valuable proxy record for a reliable construction of an orbital tuning of the early Cretaceous. An estimated age for all the different stratigraphic events recognized throughout the composite record was reported. In particular, the reestimated ages of the paleomagnetic chrons, documented in the upper part of the record, show differences with those reported by Gradstein et al. (2004) up to ∼2 m.y. The Valanginian carbon shift, present in the middle part of the composite sequence was estimated to be ∼2.3 m.y. long. The good agreement between the estimated age of the base of this positive carbon isotope excursion (∼136.34 m.y.) and the predominant volcanic phase associated to the Paranà‐Etendeka large igneous province intrusion confirmed a possible cause‐effect link between the two events.