The Bobbio Formation, traditionally subdivided into two lithological members: the Brugnello Shale (lower member) and the San Salvatore Sandstone (upper member), occurs in the core of the Bobbio tectonic window located 50 Km SW of Piacenza (Italy). It is covered tectonically by allochtonous units thrust toward the NE and is considered as the northwestern-most surface occurrence of the Cervarola Sandstone. Here we report the results of a systematic and quantitative study of the calcareous nannofossils carried out in the frame of a mapping at the 1:10.000 scale of the Bobbio window area. The calcareous nannofossils from the Bobbio Formation are represented well enough for biostratigraphic and chronostratigraphic interpretation although the biostratigraphic signal appears strongly noised. The integration of the paleontological data with the field informations has allowed the interpretation of the chronology of the Bobbio Formation. The calcareous nannofossils indicate an early Miocene age for the entire Bobbio Formation. In fact, the Brugnello Shale is Aquitanian - early Burdigalian and the San Salvatore Sandstone is late Burdigalian (the San Salvatore Sandstone contains in its lower part Sphenolithus belemnos while Sphenolithus heteromorphus is missing). According to the most recent calibration of calcareous nannofossil events, the turbidites of the San Salvatore Sandstone were deposited between 19.4 Ma and about 18 Ma at a minimum average sediment accumulation rate of the order of 140 cm/Ky (compacted thickness).

Calcareous nannofossil biostratigraphy of the Bobbio Formation (NW Apennines, Italy).

FORNACIARI, ELIANA;
1992

Abstract

The Bobbio Formation, traditionally subdivided into two lithological members: the Brugnello Shale (lower member) and the San Salvatore Sandstone (upper member), occurs in the core of the Bobbio tectonic window located 50 Km SW of Piacenza (Italy). It is covered tectonically by allochtonous units thrust toward the NE and is considered as the northwestern-most surface occurrence of the Cervarola Sandstone. Here we report the results of a systematic and quantitative study of the calcareous nannofossils carried out in the frame of a mapping at the 1:10.000 scale of the Bobbio window area. The calcareous nannofossils from the Bobbio Formation are represented well enough for biostratigraphic and chronostratigraphic interpretation although the biostratigraphic signal appears strongly noised. The integration of the paleontological data with the field informations has allowed the interpretation of the chronology of the Bobbio Formation. The calcareous nannofossils indicate an early Miocene age for the entire Bobbio Formation. In fact, the Brugnello Shale is Aquitanian - early Burdigalian and the San Salvatore Sandstone is late Burdigalian (the San Salvatore Sandstone contains in its lower part Sphenolithus belemnos while Sphenolithus heteromorphus is missing). According to the most recent calibration of calcareous nannofossil events, the turbidites of the San Salvatore Sandstone were deposited between 19.4 Ma and about 18 Ma at a minimum average sediment accumulation rate of the order of 140 cm/Ky (compacted thickness).
1992
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11577/143513
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