| Berriasian | |||||||||
|---|---|---|---|---|---|---|---|---|---|
| ~143.1 – 137.05Ma | |||||||||
| Chronology | |||||||||
| |||||||||
| Etymology | |||||||||
| Name formality | Formal | ||||||||
| Usage information | |||||||||
| Celestial body | Earth | ||||||||
| Regional usage | Global (ICS) | ||||||||
| Time scale(s) used | ICS Time Scale | ||||||||
| Definition | |||||||||
| Chronological unit | Age | ||||||||
| Stratigraphic unit | Stage | ||||||||
| Time span formality | Formal | ||||||||
| Lower boundary definition | Undefined | ||||||||
| Lower boundary definition candidates |
| ||||||||
| Lower boundary GSSP candidate section(s) | None | ||||||||
| Upper boundary definition | Undefined | ||||||||
| Upper boundary definition candidates | FAD of theCalpionellidCalpionellites darderi | ||||||||
| Upper boundary GSSP candidate section(s) | |||||||||
In thegeological timescale, theBerriasian is anage/stage of theEarly/Lower Cretaceous. It is the oldest subdivision in the entireCretaceous. It has been taken to span the time between 143.1 ±0.6Ma and 137.05 ± 0.2 (million years ago).[2] The Berriasian succeeds theTithonian (part of theJurassic) and precedes theValanginian.
The Berriasian Stage was introduced in scientific literature byHenri Coquand in 1869. It is named after the village ofBerrias in theArdèche department ofFrance.[3] The largely non-marine EnglishPurbeck Formation is in part of Berriasian age.[4] The first rocks to be described of this age were the beds of the English Purbeck Formation, named as the Purbeckian byAlexandre Brongniart in 1829 following description byHenry De la Beche,William Buckland,Thomas Webster andWilliam Henry Fitton.
The base of the Berriasian, which is also the base of the CretaceousSystem, has traditionally been placed at the first appearance of fossils of theammonite speciesBerriasella jacobi. But this is a species that has a stratigraphically problematic and geographically limited distribution. A global reference profile (aGSSP) for the Berriasian has been under active consideration by the Berriasian Working Group (ISCS) ofIUGS 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 calcareousmicrofossils, such asNannoconus,calpionellids,ammonites, palynological data andmagnetostratigraphy, notably magnetozone M19n. The calibration of these markers, especiallyNannoconus steinmannii minor,N. kamptneri minor, andCalpionella alpina, 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 adoptCalpionella 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).[5] 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.[6]
In the western part of theocean of Tethys, the Berriasian consists of four ammonitebiozones, from top to bottom (latest to earliest):
The top of the Berriasian stage is defined by the base of the Valanginian, which is fixed at the first appearance ofcalpionellid speciesCalpionellites darderi. This is just a little below the first appearance of the ammonite speciesThurmanniceras 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) .
