Cenomanian

The Cenomanian is, in the ICS' geological timescale, the oldest or earliest age of the Late Cretaceous Epoch or the lowest stage of the Upper Cretaceous Series.[4] An age is a unit of geochronology; it is a unit of time; the stage is a unit in the stratigraphic column deposited during the corresponding age. Both age and stage bear the same name.

Cenomanian
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 Planktonic Foraminifer Rotalipora globotruncanoides
Lower boundary GSSPMont Risoux, Hautes-Alpes, France
44.3925°N 5.5119°E / 44.3925; 5.5119
Lower GSSP ratified2002[2]
Upper boundary definitionFAD of the Ammonite Watinoceras devonense
Upper boundary GSSPRock Canyon, Colorado, US
38.2822°N 104.7275°W / 38.2822; -104.7275
Upper GSSP ratifiedSeptember 2003[3]

As a unit of geologic time measure, the Cenomanian Age spans the time between[5] 100.5 and 93.9 million years ago (Mya). In the geologic timescale, it is preceded by the Albian and is followed by the Turonian. The Upper Cenomanian starts around at 95 Mya.

The Cenomanian is coeval with the Woodbinian of the regional timescale of the Gulf of Mexico and the early part of the Eaglefordian of the regional timescale of the East Coast of the United States.

At the end of the Cenomanian, an anoxic event took place, called the Cenomanian-Turonian boundary event or the "Bonarelli event", that is associated with a minor extinction event for marine species.

Stratigraphic definitions

The Cenomanian was introduced in scientific literature by French palaeontologist Alcide d'Orbigny in 1847. Its name comes from the Neo-Latin name of the French city of Le Mans (département Sarthe), Cenomanum. The base of the Cenomanian Stage (which is also the base of the Upper Cretaceous Series) is placed at the first appearance of foram species Rotalipora globotruncanoides in the stratigraphic record. An official reference profile for the base of the Cenomanian (a GSSP) is located in an outcrop at the western flank of Mont Risou, near the village of Rosans in the French Alps (département Hautes-Alpes, coordinates: 44°23'33"N, 5°30'43"E). The base is, in the reference profile, located 36 meters below the top of the Marnes Bleues Formation.[6]

The top of the Cenomanian (the base of the Turonian) is at the first appearance of ammonite species Watinoceras devonense.

Important index fossils for the Cenomanian are the ammonites Calycoceras naviculare, Acanthoceras rhotomagense, and Mantelliceras mantelli.

Sequence stratigraphy and palaeoclimatology

The late Cenomanian represents the highest mean sea level observed in the Phanerozoic eon, the past 600 million years (about 150 meters above present-day sea levels). A corollary is that the highlands were at all time lows, so the landscape on Earth was one of warm broad shallow seas inundating low-lying land areas on the precursors to today's continents. What few lands rose above the waves were made of old mountains and hills, upland plateaus, all much weathered. Tectonic mountain building was minimal and most continents were isolated by large stretches of water. Without highlands to break winds, the climate would have been windy and waves large, adding to the weathering and fast rate of sediment deposition.

References
  1. International Commission on Stratigraphy. "ICS - Chart/Time Scale". www.stratigraphy.org.
  2. Kennedy, W.; Gale, A.; Lees, J.; Caron, M. (March 2004). "The Global Boundary Stratotype Section and Point (GSSP) for the base of the Cenomanian Stage, Mont Risou, Hautes-Alpes, France" (PDF). Episodes. 27: 21–32. doi:10.18814/epiiugs/2004/v27i1/003. Retrieved 13 December 2020.
  3. Kennedy, W. J.; I. Walaszczyk; W. A. Cobban (2005). "The Global Boundary Stratotype Section and Point for the base of the Turonian Stage of the Cretaceous: Pueblo, Colorado, U.S.A." (PDF). Episodes. 28 (2): 93–104. doi:10.18814/epiiugs/2005/v28i2/003.
  4. See for a detailed geologic timescale Gradstein et al. (2004)
  5. "International Stratigraphic Chart v2021/05". Archived from the original on 2021-06-05. Retrieved 2021-07-29.
  6. The GSSP for the Cenomanian was established by Kennedy et al. (2004)

Further reading
  • Gradstein, F.M.; Ogg, J.G. & Smith, A.G.; 2004: A Geologic Time Scale 2004, Cambridge University Press.
  • Kennedy, W.J.; Gale, A.S.; Lees, J.A. & Caron, M.; 2004: The Global Boundary Stratotype Section and Point (GSSP) for the base of the Cenomanian Stage, Mont Risou, Hautes-Alpes, France, Episodes 27, pp. 21–32.

44°23′33″N 5°30′43″E

This article is issued from Wikipedia. The text is licensed under Creative Commons - Attribution - Sharealike. Additional terms may apply for the media files.