The Coniacian is an
age or
stage 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 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
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 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 and followed by the
Santonian.
Stratigraphic definitions
The Coniacian is named after the city of
Cognac in the
French
French (french: français(e), link=no) may refer to:
* Something of, from, or related to France
** French language, which originated in France, and its various dialects and accents
** French people, a nation and ethnic group identified with Franc ...
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-Mar ...
. It was first defined by French geologist
Henri Coquand 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 environments ...
bivalve species ''
Cremnoceramus deformis erectus''. The official reference profile for the base (a
GSSP) 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
''Cladoceramus'' is an extinct genus of fossil Marine (ocean), marine pteriomorphian bivalves that superficially resembled the related winged pearly oysters of the Extant taxon, extant genus ''Pteria (bivalve), Pteria''. They lived in the Santoni ...
''.
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 betwee ...
, which is roughly coeval with the Coniacian and Santonian Stages. In
magnetostratigraphy, the Coniacian is part of
magnetic chronozone 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 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 (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, especiall ...
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 biozones in the
Tethys domain:
* zone of ''
Paratexanites serratomarginatus''
* zone of ''
Gauthiericeras margae''
* zone of ''
Peroniceras tridorsatum''
In the
boreal domain 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 Pr ...
.
* ; 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 - ConiacianLate 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