GSSP for Frasnian Stage

 

Definition:

The base of the Frasnian Stage which coincides with the base of the Upper Devonian is defined at the base of Bed 42' at Col du Puech de la Suque section E in southeastern Montagne Noire, France. The GSSP also coincides with the lower boundary of the Lower asymmetricus Zone which is defined by the first occurrence of the conodont Ancyrodella rotundiloba.

Location:

The GSSP section is located at Col du Puech de la Suque section E in southeastern Montagne Noire, France. The section is located on the eastern slope of the hill 358, about 50m ENE from the crest, at 1.1km SE of St. Nazaire-de-Ladarez (1:25 000 Sheet St. Chinian, x = 660.67, y = 133.95).

 

Sedimentology:

Section E is characterized by a sequence of predominantly red and grey pelagic calcilutites, punctuated by hardgrounds that are mainly in the part of the sequence above the boundary level.

 

Primary Markers:

The GSSP coincides with the first occurrence of the conodont species Ancyrodella rotundiloba.
There are 5 conodont associations recognizable in the section. In ascending order:

  1. an interval in the lowest part of the zone characterized by the early form of Ancyrodella rotundiloba.
  2. an interval with both early and late forms of Ancyrodella rotundiloba.
  3. an interval with the early form of Ancyrodella alata and late form of Ancyrodella rotundiloba.
  4. an interval with Ancyrodella rugosa and the late forms of Ancyrodella alata and Ancyrodella rotundiloba.
  5. an interval with Ancyrodella africana, Ancyrodella pramosica, the late forms of Ancyrodella alata and Ancyrodella rugosa (only in the lower part).

 

Secondary Markers:

Goniatites:
The goniatites Probeloceras and Petteroceras feisti first appear low in the Lower asymmetricus Zone.

Correlation Events:

Conodont FAD Ancyrodella rotundiloba

References:

Klapper, G., Feist, R., and House, M. R., 1987. Decision on the Boundary Stratotype for the Middle/Upper Devonian Series Boundary. Episodes 10/2, p. 97-101.



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