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 geochronol ...
. It is a subdivision of the
Late Cretaceous Epoch or
Upper Cretaceous 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-Mari ...
. 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 bivalve
Bivalvia (), in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of marine and freshwater molluscs that have laterally compressed bodies enclosed by a shell consisting of two hinged parts. As a group, bival ...
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
Bivalvia (), in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of marine and freshwater molluscs that have laterally compressed bodies enclosed by a shell consisting of two hinged parts. As a group, bival ...
''
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, 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, 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
Regression or regressions may refer to:
Science
* Marine regression, coastal advance due to falling sea level, the opposite of marine transgression
* Regression (medicine), a characteristic of diseases to express lighter symptoms or less extent ( ...
(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, causing large scale deposition of
black shales 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
Ammonoids are a group of extinct marine mollusc animals in the subclass Ammonoidea of the class Cephalopoda. These molluscs, commonly referred to as ammonites, are more closely related to living coleoids (i.e., octopuses, squid and cuttlefish) ...
biozones 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.
* ; 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