In the geologic timescale, the Callovian is an age and stage in the Middle Jurassic, lasting between 165.3 ± 1.1 annum (million years ago) and 161.5 ± 1.0 Ma.[See for a detailed geologic timescale Gradstein et al. (2004)]
Stratigraphic definitions
The Callovian Stage was first described by French palaeontologist Alcide d'Orbigny in 1852. Its name derives from the
name for
Kellaways Bridge, a small hamlet 3 km north-east of Chippenham,
Wiltshire,
England.
The base of the Callovian is defined as the place in the stratigraphic column where the ammonite genus Kepplerites first appears, which is the base of the biozone of Macrocephalites. A global reference profile (a GSSP) for the base had in 2009 not yet been assigned.
The top of the Callovian (the base of the Oxfordian) is at the first appearance of ammonite species Brightia thuouxensis.
Subdivision
The Callovian is often subdivided into three substages (or subages): Lower/Early, Middle and Upper/Late Callovian. In the
Tethys Ocean, the Callovian encompasses six ammonite biozones:
Palaeogeography
During the Callovian,
Europe was an
archipelago of a dozen or so large islands. Between them were extensive areas of continental shelf. Consequently, there are shallow marine Callovian deposits in Russia and from Belarus, through Poland and Germany, into France and eastern Spain and much of England. Around the former island coasts are frequently, land-derived sediments. These are to be found, for example, in western Scotland.
[Elmi & Babin fig.55.]
The Louann Salt and the southern Campeche Salt of the Gulf of Mexico are thought to have formed by an embayment of the Pacific Ocean across modern-day Mexico.
Literature
-
; 2002: Histoire de la Terre, Dunod, Paris (2nd ed.), .
-
; 2004: A Geologic Time Scale 2004, Cambridge University Press.
-
; 1842: Paléontologie française. 1. Terrains oolitiques ou jurassiques. 642 p, Bertrand, Paris.
External links
