Palaeoenvironment and palaeoecology before and at the onset of Oceanic Anoxic Event (OAE)1a: Reconstructions from Central Tethyan archives

In this study, a new C-isotope stratigraphy combined with a revised litho-and biostratigraphy of Barremian-Aptian platform carbonates from the central-southern Apennines (Italy) is presented. The Santa Maria (Abruzzi Region) and the Monte Faito (Campania Region) sections were investigated in order to trace platform evolution during a time of major C-cycle perturbation before and during Oceanic Anoxic Event (OAE)1a. These successions are correlated at a regional scale with the Monte Raggeto reference section (Campania) where the Selli Level Equivalent (SLE) and the Magnetic Polarity Chron CM0r were recognised in earlier studies. Significant biotic and environmental changes are documented within the Late Barremian-Early Aptian interval; in particular, the Palorbitolina lenticularis-Lithocodium-Bacinella association followed by dark-brown microbial sediments reflect considerable ecological stress upon the oligotrophic carbonate platform community (mesotrophic or even eutrophic conditions) which precedes the onset of SLE by at least 1.2 myr. Moreover, this integrated approach has resulted in an improved age control which offers the opportunity to correlate the Apenninic sections with a succession from the French Urgonian platform (Cluses section) and with pelagic records from the Italian Umbria-Marche (Gorgo a Cerbara) and Belluno (Cismon Apticore) Basins. Pelagic biozonations and magnetostratigraphy have been projected into carbonate platform sequences. A prevailing eustatic origin has been attributed to some of the lower-frequency transgressive-regressive cycles (T/RFTs) that reflect third order sea-level oscillations. The new correlations indicate that comparable biotic and environmental changes, documented around the Tethys, are not always synchronous. The type of response of biota to C-cycle perturbations before and during OAE1a depends upon palaeolatitude, palaeogeography, palaeobathymetry and regional climate patterns.