Research-paper
Planktonic foraminifera across the Campanian/Maastrichtian boundary at Tercis, south-west France
Simmons, Michael D.; Williams, Colin L.; Hancock, Jake M.
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Abstract
The Campanian/Maastrichtian boundary has been defined within both the Tethyan and Boreal realms using different, non-cosmopolitan, fossil taxa, thus inhibiting correlation of the boundary between the two palaeogeographic provinces. The idea of using palaeogeographically "intermediate" boundary sections to facilitate global correlation led to the examination of a section at Tercis, south-west France, a potential stratotype for the Campanian/Maastrichtian boundary. Previous work on macrofossils at this section had placed the boundary in a Boreal sense using ammonites and echinoderms. Planktonic foraminifera from Tercis are therefore described for the first time and their occurrence compared against the ammonite standard. Whilst being of Tethyan aspect, the fauna is of limited abundance and diversity because of a relatively shallow water depositional environment and an isolated palaeogeographic position. Many key taxa are absent, rare or unusually small. Although this limits the value of Tercis as a Campanian/Maastrichtian boundary site in the context of planktonic foraminiferal biostratigraphy, it is interesting to note that the typically Campanian restricted planktonic foraminifera, Globotruncanita elevata s.s., ranges up to approximately the base of the Maastrichtian at Tercis as defined on ammonite appearances. The use of the extinction of G. elevata s.s. as a proxy for the base of the Maastrichtian needs to be further investigated, but its apparent extinction close to the ammonite-defined boundary may be a useful event, especially since the traditional planktonic foraminiferal marker for the base of the Maastrichtian, the extinction of Globotruncanita calcarata, has been shown to significantly predate the base of the Maastrichtian as defined on the ammonite scale.