Oxfordian (stage)
The Oxfordian ( often shortened even Oxford, rarely also Oxfordian ) is in the Earth's lower chronostratigraphic stage of the Upper Jurassic series in the Jura. The stage began geochronological front of about 163.5 million years ago and ended about 157.3 million years. The Oxfordian follows the Callovian and is detached from the Kimmeridgian.
Naming and history
The term " Oxfordian " was used already in 1829 by Alexandre Brongniart, and later of Alcide d' Orbigny. It involves the Latinized name of the English city of Oxford.
Definition and GSSP
The beginning of the stage is defined by the first appearance of ammonite species Brightia thuouxensis. It ends with the first occurrence of the ammonite Pictonia baylei in the fossil record. A GSSP (Type locality and type profile ) has not yet been determined.
Subdivision of the Oxfordian
In Tethysbereich the Oxfordian is divided into six ammonite biozones:
- Epipeltoceras bimammatum
- Perishinctes bifurcatus
- Gregoryceras transversarium
- Perisphinctes plicatilis
- Cardioceras cordatum
- Quenstedtoceras mariae