The Tortonian ( often shortened to Tortonian ) is in the geologic timescale, the fifth stage of the Miocene ( Neogene ). She began geochronological about before 11.62 million years ago and ended about 7.246 million years and therefore lasted about 4.3 million years. The stage following the Serravallium and is detached from the Messinian.
Naming and history
The stage is named after the city of Tortona in the Province of Alessandria, Piedmont (Italy). The stage and the name was introduced by the Swiss geologist Karl Mayer- Eymar 1858.
Definition and GSSP
The lower boundary of the stage is defined by subquadratus the last common occurrences of calcareous Nannofossil Type Discoaster kugleri and the planktonic foraminifera species Globigerinoides. The boundary is associated with the normal short - polar magnetic polarity Subchrone C5r.2n. The upper limit is defined by the lowest occurrence of planktonic foraminifera species Globorotalia conomiozea. The limit is approximately in the center of the magnetic polarity chronozone C3Br.1r. The official type profile of the International Commission on Stratigraphy ( GSSP = " Global Stratotype Section and Point" ) is the Monte dei Corvi - beach profile at Ancona (Italy).