In the geologic timescale, the Callovian is an age and stage in the Middle Jurassic, lasting between 166.1 ± 4.0 Ma (million years ago) and 163.5 ± 4.0 Ma. It is the last stage of the Middle Jurassic, following the Bathonian and preceding the Oxfordian.[2]

Callovian
166.1 ± 1.2 – 163.5 ± 1.0 Ma
Chronology
Etymology
Name formalityFormal
Usage information
Celestial bodyEarth
Regional usageGlobal (ICS)
Time scale(s) usedICS Time Scale
Definition
Chronological unitAge
Stratigraphic unitStage
Time span formalityFormal
Lower boundary definitionFAD of the Ammonite genus Kepplerites
Lower boundary GSSP candidate section(s)
Upper boundary definitionFAD of ammonite species Brightia thuouxensis
Upper boundary GSSP candidate section(s)

Stratigraphic definitionsEdit

The Callovian Stage was first described by French palaeontologist Alcide d'Orbigny in 1852. Its name derives from the latinized 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 herveyi. 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.

SubdivisionEdit

 
Matmor Formation (Callovian, Peltoceras athleta Zone) in Makhtesh Gadol, Israel.

The Callovian is often subdivided into three substages (or subages): Lower/Early, Middle and Upper/Late Callovian. In the Tethys domain, the Callovian encompasses six ammonite biozones:

PalaeogeographyEdit

 
Callovian rocks of the Osgodby Formation[3] at Cayton Bay in North Yorkshire, England

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.[4]

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.[5]

ReferencesEdit

  1. ^ "International Chronostratigraphic Chart" (PDF). International Commission on Stratigraphy.
  2. ^ See for a detailed geologic timescale Gradstein et al. (2004)
  3. ^ "BGS Lexicon of Named Rock Units - Result Details".
  4. ^ Elmi & Babin fig.55.
  5. ^ Salvador, Amos (1987). "Late Triassic‐Jurassic Paleogeography and Origin of Gulf of Mexico Basin" (PDF). AAPG Bulletin. 71 (4): 419‐451. Retrieved 2011-03-09.[permanent dead link]

LiteratureEdit

  • Elmi, S. & Babin, C.; 2002: Histoire de la Terre, Dunod, Paris (2nd ed.), ISBN 2-10-006631-5. (in French)
  • Gradstein, F.M.; Ogg, J.G. & Smith, A.G.; 2004: A Geologic Time Scale 2004, Cambridge University Press.
  • d'Orbigny, A.C.V.M.D.; 1842: Paléontologie française. 1. Terrains oolitiques ou jurassiques. 642 p, Bertrand, Paris. (in French)

External linksEdit