In the

geological 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 geochron ...

, the Berriasian is an age/

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 ...

of the Early/Lower Cretaceous. It is the oldest subdivision in the entire

Cretaceous 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 ...

. It has been taken to span the time between 145.0 ± 4.0 Ma and 139.8 ± 3.0 Ma (million years ago). The Berriasian succeeds the Tithonian (part of the

Jurassic The Jurassic ( ) is a geologic period and stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The Jurassic constitutes the middle period of ...

) and precedes the

Valanginian In the geologic timescale, the Valanginian is an age or stage of the Early or Lower Cretaceous. It spans between 139.8 ± 3.0 Ma and 132.9 ± 2.0 Ma (million years ago). The Valanginian Stage succeeds the Berriasian Stage of the Lower Cretace ...

Stratigraphic definition

The Berriasian Stage was introduced in scientific literature by

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 1869. It is named after the village of Berrias in the Ardèche department of

France France (), officially the French Republic ( ), is a country primarily located in Western Europe. It also comprises of overseas regions and territories in the Americas and the Atlantic, Pacific and Indian Oceans. Its metropolitan area ...

. The largely non-marine English

Purbeck Formation The Purbeck Group is an Upper Jurassic to Lower Cretaceous lithostratigraphic group (a sequence of rock strata) in south-east England. The name is derived from the district known as the Isle of Purbeck in Dorset where the strata are exposed in the ...

is in part of Berriasian age.In fact, the first rocks to be described of this age were the beds of the English Purbeck Formation, named as the Purbeckian by Alexandre Brongniart in 1829 following description by

Henry De la Beche Sir Henry Thomas De la Beche KCB, FRS (10 February 179613 April 1855) was an English geologist and palaeontologist, the first director of the Geological Survey of Great Britain, who helped pioneer early geological survey methods. He was the ...

William Buckland William Buckland DD, FRS (12 March 1784 – 14 August 1856) was an English theologian who became Dean of Westminster. He was also a geologist and palaeontologist. Buckland wrote the first full account of a fossil dinosaur, which he named ' ...

, Thomas Webster and

William Henry Fitton William Henry Fitton (24 January 178013 May 1861) was an Irish physician and amateur geologist. Biography Fitton was born in Dublin and educated at Trinity College in that city. He gained the senior scholarship in 1798, and graduated in the fol ...

. The base of the Berriasian, which is also the base of the Cretaceous System, has traditionally been placed at the first appearance of fossils of the ammonite species ''

Berriasella jacobi ''Berriasella jacobi'' is an extinct species of ammonite from the late Jurassic and early Cretaceous. Because of its unique stratigraphic position, it is used as an index fossil to determine the boundary of the Cretaceous and Jurassic periods. The ...

''. But this is a species that has a stratigraphically problematic and geographically limited distribution. A global reference profile (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 ...

) for the Berriasian has been under active consideration by the Berriasian Working Group (ISCS) of IUGS since 2010. A range of contender GSSP localities has been studied in detail by the Working Group including localities as far apart as Mexico, Ukraine, Tunisia, Iraq and the Russian Far East. Several markers have been employed to refine correlations and to work towards defining a base for the Berriasian Stage. These include calcareous

microfossil A microfossil is a fossil that is generally between 0.001 mm and 1 mm in size, the visual study of which requires the use of light or electron microscopy. A fossil which can be studied with the naked eye or low-powered magnification, ...

s, such as '' Nannoconus'', calpionellids, ammonites, palynological data and

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 '' ...

, notably magnetozone M19n. The calibration of these markers, especially ''Nannoconus steinmannii minor'', ''N. kamptneri minor'', and ''

Calpionella alpina ''Calpionella'' is an extinct genus of calpionellid, a group of single celled eukaryotes.

'', within precisely fixed magnetozones give greater precision in trying to identify the best position for a boundary. In 2016, the Berriasian Working Group voted to adopt ''Calpionella alpina'' as the primary marker for the base of the Berriasian Stage. In 2019, a GSSP for the Berriasian was nominated by a vote of the Berriasian Working Group of the Cretaceous Subcommission (ISCS): it is the profile of Tré Maroua in the Vocontian Basin (Hautes Alpes, France). The GSSP was defined at the base of the Alpina Subzone in the middle of magnetozone M19n.2n. This site proposal, of Tré Maroua, was subsequently unsuccessful in a vote of the ISCS (8 votes for and 8 against: 4 not voting); a new working group was formed in 2021. In the western part of the ocean of Tethys, the Berriasian consists of four 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, from top to bottom (latest to earliest): * '' Thurmanniceras otopeta'' * '' Subthurmannia boissieri'' * '' Tirnovella occitanica'' * ''

/ Pseudosubplanites grandis'' The top of the Berriasian stage is defined by the base of the Valanginian, which is fixed at the first appearance of calpionellid species ''

Calpionellites darderi ''Calpionellites darderi'' is an extinct planktonic eukaryote and an important index fossil for the Lower Cretaceous stratigraphy. The first appearance of ''C. darderi'' marks the beginning of the Valanginian. It also defines the base of the "Cal ...

''. This is just a little below the first appearance of the ammonite species '' Thurmanniceras pertransiens''. Regional terms used in Russia include "Volgian"(which spans perhaps the latest Kimmeridgian, all the Tithonian and an uncertain amount of the lower Berriasian) and the "Ryazanian" (?upper Berriasian) .

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 ...

External links

GeoWhen Database - BerriasianJurassic-Cretaceous timescale
at the website of the subcommission for stratigraphic information of the ICS
Stratigraphic chart of the Lower Cretaceous
at the website of Norges Network of offshore records of geology and stratigraphy {{Geological history, p, m *01 Geological ages Cretaceous geochronology