Cretaceous brachiopod-rich facies of the carbonate platform-to-basin transitions in central-southern Italy: stratigraphic and paleoenvironmental significance.

The most different faunal and floral assemblages have experienced several events of extinction, diversity reduction and diversification during Cretaceous. Such events are basically coeval to rapid reorganizations of the regional-to-global hydrosphere/atmosphere systems following relevant geotectonic pulses. Biotic assemblages shifted repeatedly among phases of carbonate production modes dominated by oligotrophic specialized and meso-eutrophic opportunistic taxa, namely k- and r-mode forms, as a consequence of major turning points in the evolving paleoceanographic conditions. Stratigraphic data on several Cretaceous successions of southern Apennines and Apulia (southern Italy) have demonstrated that brachiopods were a main component of r-mode assemblages which developed in Latemost Valanginian, late Early Aptian, earlymost Cenomanian, and latemost Campanian. With the exception of the latemost Campanian event, all of these time intervals correspond to severe global environmental disruptions of the oceans and climate coupled to biocalcification crises. However, all of them correlate to Tethyan oceanic anoxic events (Weissert and Selli OAEs) and/or platform drownings (Late Valanginian, late Early Aptian, Early Cenomanian and latemost Campanian). Noteworthy, all of the investigated events reflect regional shifts among chlorozoan, foramol and microbial production modes of the mediterranean shallow-water carbonate factories. The remarkable association of brachiopoda with cyanobacteria, though in complex stratigraphic relationships, especially in Late Valanginian, late Early Aptian, and Early Cenomanian times accounts for drastic environmental deterioration of the surface oceanic waters which were highly unfavourable for oligotrophic, k-mode organisms. We assume that such a relevant correlation between Cretaceous brachiopod beds and disruptions of the paleoceanographic conditions may provide an additional tool to improve the comprehension of the internal structure of major paleoecologic changes due to the environmental collapse of oceanic waters during drowning events of carbonate platforms and/or OAEs.