Nummulitids, Lepidocyclinids and strontium isotope stratigraphy of the Porto Badisco Calcarenite (Salento Peninsula, southern Italy). Implications for the biostratigraphy and paleobiogeography of Oligocene Larger Benthic Foraminifera

Abstract

The Oligocene Porto Badisco Calcarenite (Apulian Carbonate Platform, southern Italy) contains very rich and diverse assemblages of larger benthic foraminifera. In this paper we provide the first comprehensive taxonomic study of Nummulitids and Lepidocyclinids, based on a biometric approach to species identification. The largerforaminiferal assemblage is dominated by Eulepidina, Heterostegina and Spiroclypeus. Nummulites, Operculina and Nephrolepidina make a subordinate but significant contribution. The concurrent range of the larger foraminiferal species present in the Porto Badisco Calcarenite, and in particular the presence of Spiroclypeus margaritatus and of Miogypsinoides complanatus-formosensis, indicates the late Oligocene Shallow Benthic Zone (SBZ) 23. The taxonomic composition of the larger foraminiferal assemblage of the Apulian Carbonate Platform is very similar to coeval assemblages of other localities of the western Tethyan realm (southern France, southern Spain, Malta, Greece), while some typical components of the SBZ 23 assemblages, like Heterostegina assilinoides and Eulepidina dilatata, are missing in more eastern areas (Turkey, India). Strontium isotope stratigraphy gives an age of 23.6 ± 0.5 Ma for the lower part of the Porto Badisco Calcarenite, constraining the chronostratigraphic calibration of the SBZ 23 within the latest Chattian. This calibration further supports the correlation between the SBZ 23 of the European Basins biozonal scheme with the Te 4 stage of the East Indian Letter Classification.