GSSP for the Aalenian - Bajocian Boundary

Definition:

The base of the Bajocian Stage is defined at the base of Bed AB11 of the Murtinheira Section at Cabo Mondego, Portugal. The boundary coincides with the first occurrrence of the ammonite assemblage characterized by Hyperlioceras mundum, Hyperlioceras furcatum, Braunsina aspera, and Braunsina elegantula. The GSSP lies just below the nanno-horizon of the entry of Watznaueria communis and Watznaueria fossacincta, and closely corresponds with an inversion to normal polarity correlated with the Jurassic magnetic polarity time scale.

Location:

The GSSP of the Bajocian Stage is located on the Portuguese Atlantic coast, 40km west of Coimbra and 7km north of Figueira da Foz. The Murtinheira Section is at the foot of Cabo Mondego cliff, south-west of the village of Murtinheira. The GSSP is shown on the 1:25 000 scale topographic map of Vais (Sheet 238A) by coordinates M = 134.4, P = 359.2.		 click


Sedimentology:

The GSSP succession corresponds to a more or less rhythmic alternation of gray limestones and marls, sometimes fossiliferous (ammonite, brachiopods), with bioturbation marks and coal fragments.
The Aalenian – Bajocian Boundary is defined at 77.8m from the base of the section at the base of Bed AB 11. 		click


Primary Markers:

Ammonites:
The boundary coincides with the first occurrrence of the ammonite assemblage characterized by Hyperlioceras mundum, Hyperlioceras furcatum, Braunsina aspera, and Braunsina elegantula.

Secondary Markers:

Nannofossils:
The GSSP lies just below the first occurrence of Watznaueria communis and Watznaueria fossacincta
Magnetostratigraphy
The GSSP coincides with an inversion from reversed to normal polarity.

References:

Pavia, G. and Enay, R., 1997. Definiton of the Aalenian – Bajocian Stage Boundary. Episodes 20/1, p.16 – 22.