The Turonian is, in the
ICS
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'
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 ...
, the second
age
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Time and its effects
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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 by the
Cenomanian
The Cenomanian is, in the ICS' geological timescale, the oldest or earliest age of the Late Cretaceous Epoch or the lowest stage of the Upper Cretaceous Series. An age is a unit of geochronology; it is a unit of time; the stage is a unit in the s ...
Stage and underlies the
Coniacian
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 89.8 ± 1 Ma and 86.3 ± 0.7 Ma (million years ago). The Coniacian is preceded by t ...
Stage.
At the beginning of the Turonian an
oceanic 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 2) took place, also referred to as the
Cenomanian-Turonian boundary event or the "Bonarelli Event".
Stratigraphic definition
The Turonian (French: ''Turonien'') was defined by the
French
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** French language, which originated in France, and its various dialects and accents
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paleontologist
Alcide d'Orbigny (1802–1857) in 1842. Orbigny named it after the French city of
Tours in the region of
Touraine (department
Indre-et-Loire), which is the original
type locality.
The base of the Turonian Stage is defined as the place where the
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) ...
species ''
Watinoceras devonense'' first appears in the
stratigraphic column. The official reference profile (the
GSSP) for the base of the Turonian is located in the Rock Canyon anticline near
Pueblo, Colorado (United States, coordinates: 38° 16' 56" N, 104° 43' 39" W).
[The GSSP was established by Kennedy ''et al.'' (2005)]
The top of the Turonian Stage (the base of the Coniacian) is defined as the place in the stratigraphic column where 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
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 rotundatus
''Cremnoceramus'' ("cremno-" = ''kremnos'' reek precipice or over hanging wall or bank; "ceramus" = ''keramos'' reek clay pot) is an extinct genus of fossil marine pteriomorphian bivalves that superficially resembled the related winged pearly oy ...
'' first appears.
Subdivision
The Turonian is sometimes subdivided in Lower/Early, Middle and Upper/Late substages or subages. In the
Tethys domain, it contains the following ammonite
biozones:
*zone of ''
Subprionocyclus neptuni'' (in the Upper Turonian)
*zone of ''
Collignoniceras woollgari'' (in the Middle Turonian)
*zone of ''
Mammites nodosoides''
*zone of ''
Watinoceras coloradoense'' or ''Watinoceras devonense'' (last two both in the Lower Turonian)
Other important
index fossils are species of the inoceramid
genus ''
Inoceramus'' (''I. schloenbachi'', ''I. lamarcki'' and ''I. labiatus''). Inoceramids are bivalve
Mollusca
Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000 extant species of molluscs are recognized. The number of fossil species is esti ...
related to today's
mussels.
References
Literature
*; 2004: ''A Geologic Time Scale 2004'',
Cambridge University Press.
*; 2005: ''The Global Boundary Stratotype Section and Point for the base of the Turonian Stage of the Cretaceous: Pueblo, Colorado, U.S.A.'', Episodes 28(2): pp 93–104.
External links
GeoWhen Database - TuronianLate Cretaceous timescale
at the website of the subcommission for stratigraphic information of the ICS
*Stratigraphic charts of the Cretaceous
an
at the website of Norges Network of offshore records of geology and stratigraphy
Turonian Microfossils: 48 images of Foraminifera
{{Geological history, p, m
Turonian,
*02
Geological ages
Cretaceous geochronology