Bio-chemostratigraphy of the Barremian-Aptian shallow-water carbonates of the southern Apennines (Italy): Pinpointing the OAE1a in a Tethyan carbonate platform

Abstract

Low biostratigraphic resolution and lack of chronostratigraphic calibration hinder precise correlations between platform carbonates and coeval deep-water succes-sions. These are the main obstacle when studying the record of Mesozoic oceanic anoxic events in carbonate platforms. In this paper carbon and strontium isotope stratigraphy are used to produce the first chronostratigraphic calibration of the Barremian-Aptian biostratigraphy of the Apenninic car-bonate platform of southern Italy. According to this cali-bration, the segment of decreasing δ13C values, leading to the negative peak that is generally taken as the onset of the Selli event, starts a few metres above the last occurrence of Palorbitolina lenticularis and Voloshinoides murgensis. The following rise of δ13C values, corresponding to the interval of enhanced accumulation of organic matter in deep-water sections, ends just below the first acme of Salpingoporella dinarica, which roughly corresponds to the segment of peak δ13C values. The whole carbon isotope excursion associ-ated with the oceanic anoxic event la is bracketed in the Apenninic carbonate platform between the last occurrence of Voloshinoides murgensis and the "Orbitolina level", charac-terized by the association of Mesorbitolina parva and Mesor-bitolina texana. Since these bioevents have been widely rec-ognized beyond the Apenninic platform, the calibration pre-sented in this paper can be used to pinpoint the interval cor-responding to the Early Aptian oceanic anoxic event in other carbonate platforms of central and southern Tethys. This cal-ibration will be particularly useful to interpret the record of the Selli event in carbonate platform sections for which a re-liable carbon isotope stratigraphy is not available.