Integrated stratigraphy of the middle - upper Miocene deposits of San Bartolomeo Formation, cropping out whithin the geological map n.405 Campobasso (Molise, Ssouthern Italy)

Abstract

The San Bartolomeo Formation was established by CROSTELLA & VEZZAN(I1 964), and consists of about 1000 m thick siliciclastic and turbiditic sedimentary succession, which lies in angular unconformity over the Sannio Unit (PATACCA& SCANDONE, 2007). As far as the age, this formation has been controversially considered Serravallian -Tortonian (CROSTELLA & VEZZANI, 1964), Serravallian (TORTORICI1, 975), Langhian - Tortonian (PESCATORE, 1971; DAZZARO et alii, 1988), latemost Tortonian?/early Messinian (PATACCA & SCANDONE, 2007). Moreover the tectono-sedimentary environment of these deposits is also questionable considered: foredeep basin (Cocco el alii, 1972), piggy-back basin (Dazzaro et alii, 1988; Dl NOCERA el alii, 1988; PATACCAet alii, 1990), thrust- related basin (BOLANO, 2000), thrust-top or wedge -top basin (PESCATOReEt alii,1996; PESCATOREet alii, 2000) and thrust -sheet-top basin (PATACCA & SCANDONE, 2007'). The deposits of San Bartolomeo Formation widely outcrop in the center-eastem part of the geological map N. 405, Campobasso, of the National Geological Map Series of Italy (at scale 1:50,000). In this area the studied formation consists of a succession, about 600 m thick, of siliciclastic and turbiditic sediments composed by three main lithofacies: a) arenaceous and lor arenaceous-conglomerate; b) pelitic-arenaceous: and c) pelitic. The age of the investigated sediments was established on the basis of integrated calcareous plankton hiostratigraphy (calcareous nannofossils and planktonic foraminifera). A total of 164 samples were collected for biostratigraphic studies, with a sample resolution of 50 centimetres to 2 m, along seven stratigraphical sections, logged and measured between Casalciprano village, at North, and Baranello village at South.The analyses of calcareous nannofossil and planktonic foraminifera1 assemblages were performed following the procedures extensively used in Mediterranean and extra- Meditexanean biostratigraphic studies (Dl STEFANO el alii, 2008, and references therein), and the zonal assignment followed the biostratigraphic schemes of SPROVIEReIt alii (2002) and DI STEFANOet alii (2008). Based on the integrated biostratigraphic study the San Bartolomeo Formation, cropping out in Campobasso area, encompasses the early Serravallian - middlellate? Tortonian stratigraphic internal, between the calcareous nannofossil zones MNN6a and MNNBlMNN9, and the planktonic foraminiferal zones MMi5 through MMi 1 1. The biostratigraphic results presented and the detailed field observations carried out for mapping the Campobasso geological map, would suggest a reassessment of the San Bartolomeo Formation chronostratigraphy, the Sannio Unit paleogeographic position, and the tectono-sedimentary evolution of the Southern Apennines during the Serravallian age.