The Cenomanian is, in the
ICS'
geological timescale, the oldest or earliest
age of the
Late Cretaceous
The Late Cretaceous (100.5–66 Ma) is the younger 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 ''creta'', ...
Epoch
In chronology and periodization, an epoch or reference epoch is an instant in time chosen as the origin of a particular calendar era. The "epoch" serves as a reference point from which time is measured.
The moment of epoch is usually decided ...
or the lowest
stage of the
Upper Cretaceous
The Late Cretaceous (100.5–66 Ma) is the younger 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 ''creta'', ...
Series. 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.
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 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
The Gulf of Mexico ( es, Golfo de México) is an ocean basin and a marginal sea of the Atlantic Ocean, largely surrounded by the North American continent. It is bounded on the northeast, north and northwest by the Gulf Coast of the United ...
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
Paleontology (), also spelled palaeontology or palæontology, is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene epoch (roughly 11,700 years before present). It includes the study of foss ...
Alcide d'Orbigny in 1847. Its name comes from the
New 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
Mont may refer to:
Places
* Mont., an abbreviation for Montana, a U.S. state
* Mont, Belgium (disambiguation), several places in Belgium
* Mont, Hautes-Pyrénées, a commune in France
* Mont, Pyrénées-Atlantiques, a commune in France
* Mont, Saà ...
, near the village of
Rosans in the French
Alps
The Alps () ; german: Alpen ; it, Alpi ; rm, Alps ; sl, Alpe . are the highest and most extensive mountain range system that lies entirely in Europe, stretching approximately across seven Alpine countries (from west to east): France, Sw ...
(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 GSSP for the Cenomanian was established by Kennedy ''et al.'' (2004)]
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
There are several kinds of mean in mathematics, especially in statistics. Each mean serves to summarize a given group of data, often to better understand the overall value ( magnitude and sign) of a given data set.
For a data set, the '' ...
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 (; ; ), 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. Often one or more sides ...
s, 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
Further reading
*Gradstein, F.M.; Ogg, J.G. & Smith, A.G.; 2004: ''A Geologic Time Scale 2004'',
Cambridge University Press
Cambridge University Press is the university press of the University of Cambridge. Granted letters patent by King Henry VIII in 1534, it is the oldest university press in the world. It is also the King's Printer.
Cambridge University Pr ...
.
*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.
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