GSSP of the Hauterivian Stage
Definition
The GSSP for the base of the Hauterivian Stage is defined in the La Charce section (Vocontian Basin, southeastern France) at the base of bed number 189 (bed numbering system according to Reboulet et al., 1992).
The base of bed 189 coincides with the First Occurrence (FO) of the ammonite genus Acanthodiscus (species A. rebouli), which marks the base of the lowermost Hauterivian Acanthodiscus radiatus ammonite Zone. The FO of A. radiatus lies four beds higher in the succession (bed 193).
Location
The GSSP section (coordinates: 44°28’10.0″N, 5°26’37.4″E, altitude 620 m) is exposed about 550 m west of La Charce village, about 70 km southeast of Valence and approximately 35 km south of Die in the Department of Drôme, southeastern France. The lower part of the section crops out on the eastern escarpment of the Serre-de-l’Ane (between the electric line and Road D 61) then the section is exposed along the side of the road.
Sedimentology
The interval of the La Charce section which embraces the Valanginian/Hauterivian boundary is 40 m thick and is included in the “Calcaires marneux à Hoplites” sensu Paquier (1900). It consists of alternated limestone and marly layers that have been interpreted to represent cyclic variations of calcareous nannofossils caused by climatic changes on the Milankovitch scale.
Primary Marker
The FO of the ammonite genus Acanthodiscus, which marks the base of the A. radiatus ammonite Zone at the base of bed number 189 (bed numbering system after Reboulet et al., 1992).
Secondary Markers
Listed below from the stratigraphic top to the bottom (FO = First Occurrence; LO = Last Occurrence)
Bed 217: FO of Diloma galiciense (calcareous nannofossil)
Bed 214: FO of Saynella mucronata (ammonite)
Bed 213: LO of Eiffelithus windii and LO of Tribrachiatus sp. (calcareous nannofossils)
Bed 197: FO of Leopoldia leopoldina (ammonite)
Bed 194: FO of Spitidiscus (gr. lorioli-meneghinii) (ammonite)
Bed 193: FO of Breistrofferella castellanensis (ammonite)
Bed 190: FO of Breistrofferella varapensis (ammonite) and FO of Staurolithites mitcheneri (calcareous nannofossil)
Bed 189: FO of Teschenites flucticulus (ammonite) and FO of Teschenites pachydicranus (ammonite)
Bed 186: LO of Teschenites callidiscus (ammonite)
Correlation Events
The top of Chron M10Nn.3n coincides with the base of the Hauterivian.
Carbon isotopes from carbonate bulk rock samples show a plateau of around 1.3‰ across the Valanginian/Hauterivian boundary.