The Coniacian is an

age Age or AGE may refer to: Time and its effects * Age, the amount of time someone or something has been alive or has existed ** East Asian age reckoning, an Asian system of marking age starting at 1 * Ageing or aging, the process of becoming older ...

stage Stage or stages may refer to: Acting * Stage (theatre), a space for the performance of theatrical productions * Theatre, a branch of the performing arts, often referred to as "the stage" * ''The Stage'', a weekly British theatre newspaper * Sta ...

in the

geologic timescale The geologic time scale, or geological time scale, (GTS) is a representation of time based on the rock record of Earth. It is a system of chronological dating that uses chronostratigraphy (the process of relating strata to time) and geochr ...

. It is a subdivision 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 by ...

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'', th ...

Series Series may refer to: People with the name * Caroline Series (born 1951), English mathematician, daughter of George Series * George Series (1920–1995), English physicist Arts, entertainment, and media Music * Series, the ordered sets used in ...

and spans the time between 89.8 ± 1 Ma and 86.3 ± 0.7 Ma (million years ago). The Coniacian is preceded by the

Turonian The Turonian is, in the ICS' geologic timescale, the second age in the Late Cretaceous Epoch, or a stage in the Upper Cretaceous Series. It spans the time between 93.9 ± 0.8 Ma and 89.8 ± 1 Ma (million years ago). The Turonian is preceded b ...

and followed by the

Santonian The Santonian is an age in the geologic timescale or a chronostratigraphic stage. It is a subdivision of the Late Cretaceous Epoch or Upper Cretaceous Series. It spans the time between 86.3 ± 0.7 mya (million years ago) and 83.6 ± 0.7 mya. ...

Stratigraphic definitions

The Coniacian is named after the city of

Cognac Cognac ( , also , ) is a variety of brandy named after the commune of Cognac, France. It is produced in the surrounding wine-growing region in the departments of Charente and Charente-Maritime. Cognac production falls under French appella ...

in the French region of

Saintonge Saintonge may refer to: *County of Saintonge, a historical province of France on the Atlantic coast *Saintonge (region), a region of France corresponding to the historical province Places *Saint-Genis-de-Saintonge, a commune in the Charente-Mari ...

. It was first defined by French geologist

Henri Coquand Henri Coquand (1813, in Aix-en-Provence – 1881, in Marseille) was a French geologist and paleontologist. In 1841 he obtained his doctorate in sciences in Paris, and later served as a professor of geology at the University of Besançon, Poitie ...

in 1857. The base of the Coniacian Stage is at the first appearance of the

inoceramid The Inoceramidae are an extinct family of bivalves ("clams") in the Class Mollusca. Fossils of inoceramids are found in marine sediments of Permian to latest Cretaceous in age. Inoceramids tended to live in upper bathyal and neritic environment ...

bivalve species '' Cremnoceramus deformis erectus''. The official reference profile for the base (a

GSSP A Global Boundary Stratotype Section and Point (GSSP) is an internationally agreed upon reference point on a stratigraphic section which defines the lower boundary of a stage on the geologic time scale. The effort to define GSSPs is conducted ...

) is located in Salzgitter-Salder, Lower Saxony, Germany. The top of the Coniacian (the base of the Santonian Stage) is defined by the appearance of the inoceramid bivalve '' Cladoceramus undulatoplicatus''. The Coniacian overlaps the regional Emscherian Stage of

Germany Germany,, officially the Federal Republic of Germany, is a country in Central Europe. It is the second most populous country in Europe after Russia, and the most populous member state of the European Union. Germany is situated betwe ...

, which is roughly coeval with the Coniacian and Santonian Stages. In

magnetostratigraphy Magnetostratigraphy is a geophysical correlation technique used to date sedimentary and volcanic sequences. The method works by collecting oriented samples at measured intervals throughout the section. The samples are analyzed to determine their '' ...

, the Coniacian is part of

magnetic chronozone Magnetism is the class of physical attributes that are mediated by a magnetic field, which refers to the capacity to induce attractive and repulsive phenomena in other entities. Electric currents and the magnetic moments of elementary particles ...

C34, the so-called

Cretaceous Magnetic Quiet Zone The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of th ...

, a relatively long period with normal polarity.

Sequence stratigraphy and geochemistry

After a maximum of the global sea level during the early Turonian, the Coniacian was characterized by a gradual fall of the sea level. This cycle is in

sequence stratigraphy Sequence stratigraphy is a branch of geology, specifically a branch of stratigraphy, that attempts to discern and understand historic geology through time by subdividing and linking sedimentary deposits into unconformity bounded units on a variety ...

seen as a first order cycle. During the middle Coniacian a shorter, second order cycle, caused a temporary rise of the sea level (and global transgressions) on top of the longer first order trend. The following regression (Co1, at 87,0 Ma) separates the Middle from the Upper Coniacian Substage. An even shorter third order cycle caused a new transgression during the Late Coniacian. Beginning in the Middle Coniacian, an

anoxic event Oceanic anoxic events or anoxic events ( anoxia conditions) describe periods 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 ...

(OAE-3) occurred in the

Atlantic Ocean The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the " Old World" of Africa, Europe ...

, causing large scale deposition of

black shale Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4) and tiny fragments (silt-sized particles) of other minerals, especia ...

s in the Atlantic domain. The anoxic event lasted till the Middle Santonian (from 87.3 to 84.6 Ma) and is the longest and last such event during the Cretaceous period.See Meyers ''et al.'' (2006)

Subdivision

The Coniacian is often subdivided into Lower, Middle and Upper Substages. It encompasses three ammonite

biozone In biostratigraphy, biostratigraphic units or biozones are intervals of geological strata that are defined on the basis of their characteristic fossil taxa, as opposed to a lithostratigraphic unit which is defined by the lithological properties ...

s in the Tethys domain: * zone of '' Paratexanites serratomarginatus'' * zone of '' Gauthiericeras margae'' * zone of '' Peroniceras tridorsatum'' In the

boreal domain Boreal may refer to: Climatology and geography *Boreal (age), the first climatic phase of the Blytt-Sernander sequence of northern Europe, during the Holocene epoch *Boreal climate, a climate characterized by long winters and short, cool to mild ...

the Coniacian overlaps just one ammonite biozone: that of '' Forresteria petrocoriensis''

References

Notes

Literature

* ; 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 Pre ...

. * ; 2006: ''Origins and accumulation of organic matter in expanded Albian to Santonian black shale sequences on the Demerara Rise, South American margin'', Organic Geochemistry 37, pp 1816–1830.

External links

GeoWhen Database - Coniacian

Late Cretaceous timescale
at the website of the subcommission for stratigraphic information of the ICS
Stratigraphic chart of the Late Cretaceous
at the website of Norges Network of offshore records of geology and stratigraphy {{Geological history, p, m *03 Geological ages Cretaceous geochronology