The Cenomanian is, in the

International Commission on Stratigraphy The International Commission on Stratigraphy (ICS), sometimes unofficially referred to as the International Stratigraphic Commission, is a daughter or major subcommittee grade scientific organization that concerns itself with stratigraphy, strati ...

's (ICS) geological timescale, the oldest or earliest age of the

Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the more recent of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''cre ...

Epoch or the lowest stage of the Upper Cretaceous Series. An age is a unit of

geochronology Geochronology is the science of Chronological dating, determining the age of rock (geology), rocks, fossils, and sediments using signatures inherent in the rocks themselves. Absolute geochronology can be accomplished through radioactive isotopes, ...

; 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. As a unit of geologic time measure, the Cenomanian Age spans the time between 100.5 and 93.9 million years ago (Mya). In the geologic timescale, it is preceded by the

Albian The Albian is both an age (geology), age of the geologic timescale and a stage (stratigraphy), stage in the stratigraphic column. It is the youngest or uppermost subdivision of the Early Cretaceous, Early/Lower Cretaceous epoch (geology), Epoch/s ...

and is followed by the

Turonian The Turonian is, in the International Commission on Stratigraphy, ICS' geologic timescale, the second age (geology), age in the Late Cretaceous epoch (geology), Epoch, or a stage (stratigraphy), stage in the Upper Cretaceous series (stratigraphy), ...

. The Upper Cenomanian starts around at 95 Mya. The Cenomanian is coeval with the Woodbinian of the regional timescale of the

Gulf of Mexico The Gulf of Mexico () is an oceanic basin and a marginal sea of the Atlantic Ocean, mostly surrounded by the North American continent. It is bounded on the northeast, north, and northwest by the Gulf Coast of the United States; on the southw ...

and the early part of the Eaglefordian of the regional timescale of the

East Coast of the United States The East Coast of the United States, also known as the Eastern Seaboard, the Atlantic Coast, and the Atlantic Seaboard, is the region encompassing the coast, coastline where the Eastern United States meets the Atlantic Ocean; it has always pla ...

. At the end of the Cenomanian, an

anoxic event An anoxic event describes a period wherein large expanses of Earth's oceans were depleted of dissolved oxygen (O2), creating toxic, euxinic ( anoxic and sulfidic) waters. Although anoxic events have not happened for millions of years, the geol ...

took place, called the Cenomanian-Turonian boundary event or the "Bonarelli event", that is associated with a minor extinction event for marine species. '' Cenomanithrips'', an extinct thrip of the Stenurothripidae family, was named after the Cenomanian, the age of the Myanmar amber in which it was discovered.

Stratigraphic definitions

The Cenomanian was introduced in scientific literature by French

palaeontologist Paleontology, also spelled as palaeontology or palæontology, is the scientific study of the life of the past, mainly but not exclusively through the study of fossils. Paleontologists use fossils as a means to classify organisms, measure geolo ...

Alcide d'Orbigny Alcide Charles Victor Marie Dessalines d'Orbigny (6 September 1802 – 30 June 1857) was a French naturalist who made major contributions in many areas, including zoology (including malacology), palaeontology, geology, archaeology and anthropol ...

in 1847. Its name comes from the

Neo-Latin Neo-LatinSidwell, Keith ''Classical Latin-Medieval Latin-Neo Latin'' in ; others, throughout. (also known as New Latin and Modern Latin) is the style of written Latin used in original literary, scholarly, and scientific works, first in Italy d ...

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 A Global Boundary Stratotype Section and Point (GSSP), sometimes referred to as a golden spike, is an internationally agreed upon reference point on a stratigraphic section which defines the lower boundary of a stage on the geologic time scale. ...

) is located in an

outcrop An outcrop or rocky outcrop is a visible exposure of bedrock or ancient superficial deposits on the surface of the Earth and other terrestrial planets. Features Outcrops do not cover the majority of the Earth's land surface because in most p ...

at the western flank of Mont Risou, near the village of Rosans in the French

Alps The Alps () are some of the highest and most extensive mountain ranges in Europe, stretching approximately across eight Alpine countries (from west to east): Monaco, France, Switzerland, Italy, Liechtenstein, Germany, Austria and Slovenia. ...

(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. The top of the Cenomanian (the base of the Turonian) is at the first appearance of

ammonite Ammonoids are extinct, (typically) coiled-shelled cephalopods comprising the subclass Ammonoidea. They are more closely related to living octopuses, squid, and cuttlefish (which comprise the clade Coleoidea) than they are to nautiluses (family N ...

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

plateau In geology and physical geography, a plateau (; ; : plateaus or plateaux), also called a high plain or a tableland, is an area of a highland consisting of flat terrain that is raised sharply above the surrounding area on at least one side. ...

s, all much weathered.

Tectonic Tectonics ( via Latin ) are the processes that result in the structure and properties of the Earth's crust and its evolution through time. The field of ''planetary tectonics'' extends the concept to other planets and moons. These processes ...

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. The Early Cenomanian was extremely hot, with mid-latitude sea surface temperatures (SSTs) estimated at >31°C and water temperatures in the upper bathyal depths estimated at >17 °C. During the Cenomanian, Labrador's mean annual temperature (MAT) was around 15.1 ± 2.1°C, one of the coldest in North America at this time.

Egypt Egypt ( , ), officially the Arab Republic of Egypt, is a country spanning the Northeast Africa, northeast corner of Africa and Western Asia, southwest corner of Asia via the Sinai Peninsula. It is bordered by the Mediterranean Sea to northe ...

was warm and humid, though occasionally saw intervals of relatively dry conditions.

References

External links

GeoWhen Database - CenomanianLate Cretaceous timescale
at the website of the subcommission for stratigraphic information of the ICS
Stratigraphic chart of the Lower Cretaceous (including the Cenomanian)
at the website of Norges Network of offshore records of geology and stratigraphy
Cenomanian Microfossils: 20+ images of Foraminifera
{{Coord, 44, 23, 33, N, 5, 30, 43, E, source:itwiki, display=title *01 Geological ages Cretaceous geochronology

Stratigraphic definitions

Sequence stratigraphy and palaeoclimatology

References

Further reading

External links