Coniacian
Encyclopedia
The Coniacian is an age or stage in the geologic timescale. It is a subdivision of the Late Cretaceous
epoch
or Upper Cretaceous series
and spans the time between 89.3 ± 1 Ma and 85.8 ± 0.7 Ma (million years ago). The Coniacian is preceded by the Turonian
and followed by the Santonian
.
in the French
region of Saintonge
. 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 species Cremnoceramus rotundatus. An official reference profile for the base (a GSSP) had in 2009 not yet been appointed.
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
, 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.
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
, 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.
biozone
s in the Tethys domain
:
In the boreal domain the Coniacian overlaps just one ammonite biozone: that of Forresteria petrocoriensis
.; 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.
Late Cretaceous
The Late Cretaceous is the younger of two epochs into which the Cretaceous period is divided in the geologic timescale. Rock strata from this epoch form the Upper Cretaceous series...
epoch
Epoch (geology)
An epoch is a subdivision of the geologic timescale based on rock layering. In order, the higher subdivisions are periods, eras and eons. We are currently living in the Holocene epoch...
or Upper Cretaceous series
Series (stratigraphy)
Series are subdivisions of rock layers made based on the age of the rock and corresponding to the dating system unit called an epoch, both being formally defined international conventions of the geological timescale. A series is therefore a sequence of rock depositions defining a...
and spans the time between 89.3 ± 1 Ma and 85.8 ± 0.7 Ma (million years ago). The Coniacian is preceded by the Turonian
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 93.5 ± 0.8 Ma and 89.3 ± 1 Ma...
and followed by the Santonian
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 85.8 ± 0.7 mya and 83.5 ± 0.7 mya...
.
Stratigraphic definitions
The Coniacian is named after the city of CognacCognac
Cognac is a commune in the Charente department in southwestern France. It is a sub-prefecture of the department.-Geography:Cognac is situated on the river Charente between the towns of Angoulême and Saintes. The majority of the town has been built on the river's left bank, with the smaller right...
in the French
France
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...
region of Saintonge
Saintonge
Saintonge is a small region on the Atlantic coast of France within the département Charente-Maritime, west and south of Charente in the administrative region of Poitou-Charentes....
. 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
Inoceramidae
Inoceramidae was a family of prehistoric clams. Inoceramids tended to live in upper bathyal and neritic environments. In Alaska's Matanuska Formation, the most abundant mollusks in the quarry containing the Talkeetna Mountains Hadrosaur were inoceramids....
bivalve species Cremnoceramus rotundatus. An official reference profile for the base (a GSSP) had in 2009 not yet been appointed.
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
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
, which is roughly coeval with the Coniacian and Santonian stages. In magnetostratigraphy
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 characteristic remanent magnetization , that is, the...
, 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 stratigraphySequence stratigraphy
Sequence stratigraphy is a branch of geology that attempts to subdivide and link sedimentary deposits into unconformity bound units on a variety of scales and explain these stratigraphic units in terms of variations in sediment supply and variations in the rate of change in accommodation space...
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
Transgression (geology)
A marine transgression is a geologic event during which sea level rises relative to the land and the shoreline moves toward higher ground, resulting in flooding. Transgressions can be caused either by the land sinking or the ocean basins filling with water...
) on top of the longer first order trend. The following regression
Marine regression
Marine regression is a geological process occurring when areas of submerged seafloor are exposed above the sea level. The opposite event, marine transgression, occurs when flooding from the sea covers previously exposed land....
(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
Anoxic event
Oceanic anoxic events or anoxic events occur when the Earth's oceans become completely depleted of oxygen below the surface levels. Although anoxic events have not happened for millions of years, the geological record shows that they happened many times in the past. Anoxic events may have caused...
(OAE-3) occurred in the Atlantic Ocean
Atlantic Ocean
The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...
, 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.
Subdivision
The Coniacian is often subdivided into Lower, Middle and Upper substages. It encompasses three ammoniteAmmonite
Ammonite, as a zoological or paleontological term, refers to any member of the Ammonoidea an extinct subclass within the Molluscan class Cephalopoda which are more closely related to living coleoids Ammonite, as a zoological or paleontological term, refers to any member of the Ammonoidea an extinct...
biozone
Biozone
Biostratigraphic units or Biozones are intervals of geological strata that are defined on the basis of their characteristic fossil taxa....
s in the Tethys domain
Tethys Ocean
The Tethys Ocean was an ocean that existed between the continents of Gondwana and Laurasia during the Mesozoic era before the opening of the Indian Ocean.-Modern theory:...
:
- 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
Forresteria
Forresteria is an extinct genus of cephalopod belonging to the Ammonite subclass. They flourished during the late Turonian and early Coniacian ages, and were global in extent...
†Ornithopods
| Ornithopoda of the Coniacian | ||||
|---|---|---|---|---|
| Taxa | Presence | Location | Description | Images |
Bactrosaurus Bactrosaurus Bactrosaurus is a genus of herbivorous dinosaur that lived in east China during the late Cretaceous, about 70 mya. The position Bactrosaurus occupies in the Cretaceous makes it one of the earliest known hadrosaurs, and although it is not known from a full skeleton, Bactrosaurus is one of the best... |
Turonian 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 93.5 ± 0.8 Ma and 89.3 ± 1 Ma... to Coniacian |
Gobi Desert Gobi Desert The Gobi is a large desert region in Asia. It covers parts of northern and northwestern China, and of southern Mongolia. The desert basins of the Gobi are bounded by the Altai Mountains and the grasslands and steppes of Mongolia on the north, by the Hexi Corridor and Tibetan Plateau to the... , Mongolia and China |
Would have been 6 m (20 ft) long[1] and 2 m (7 ft) high when in the quadrupedal stance, and weighed 1100 - 1500 kg (2400 - 3300 lb). Like many hadrosaurs, it could switch between bipedal and quadrupedal stances, but unusually it had large spines protruding from the vertebrae. |  |
Macrogryphosaurus Macrogryphosaurus Macrogryphosaurus is a genus of basal iguanodont dinosaur from the Turonian-early Coniacian age Upper Cretaceous Portezuelo Formation of Patagonia, Argentina. It was described by Jorge Calvo and colleagues, with M... |
Turonian 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 93.5 ± 0.8 Ma and 89.3 ± 1 Ma... to early Coniacian |
Portezuelo Formation Portezuelo Formation The Portezuelo Formation is a geologic formation outcropping in the Mendoza, Río Negro and Neuquén provinces of Argentina. It is the fourth-oldest formation in the Neuquén Group and the older of the two formations in the Río Neuquén Subgroup... , Argentina |
A genus of basal iguanodont, a large bipedal herbivore | |
Literature
; 2004: A Geologic Time Scale 2004, Cambridge University PressCambridge University Press
Cambridge University Press is the publishing business of the University of Cambridge. Granted letters patent by Henry VIII in 1534, it is the world's oldest publishing house, and the second largest university press in the world...
.; 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