| Gelasian | |||||||||
|---|---|---|---|---|---|---|---|---|---|
| 2.58 – 1.80Ma | |||||||||
| Chronology | |||||||||
| |||||||||
| Formerly part of | TertiaryPeriod/System PlioceneEpoch/Series | ||||||||
| 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 |
| ||||||||
| Lower boundary GSSP | Monte San Nicola Section,Gela,Sicily,Italy 37°08′49″N14°12′13″E / 37.1469°N 14.2035°E /37.1469; 14.2035 | ||||||||
| Lower GSSP ratified | 1996 (as base of Gelasian)[2] | ||||||||
| Upper boundary definition | Approximately 8 m after the end of magnetic polaritychronozone C2n (Olduvai). | ||||||||
| Upper boundary GSSP | Vrica Section,Calabria, Italy 39°02′19″N17°08′05″E / 39.0385°N 17.1348°E /39.0385; 17.1348 | ||||||||
| Upper GSSP ratified | 5 December 2011 (as base of Calabrian)[3] | ||||||||
TheGelasian is anage in the internationalgeologic timescale or astage inchronostratigraphy, being the earliest or lowest subdivision of theQuaternary Period/System andPleistocene Epoch/Series. It spans the time between 2.58Ma (million years ago) and 1.80 Ma.[4] It follows thePiacenzian Stage (part of thePliocene) and is followed by theCalabrian Stage.
The Gelasian was introduced in the geologic timescale in 1998.[5] It is named after theSicilian city ofGela in the south of the island. In 2009 it was moved from thePliocene to thePleistocene so that thegeologic time scale would be more consistent with the key changes in Earth's climate, oceans, and biota that occurred 2.58 million years ago.[6]
The base of the Gelasian is definedmagnetostratigraphically as the base of the Matuyama (C2r)chronozone (at theGauss-Matuyama magnetostratigraphic boundary), isotopic stage 103. Above this line notable extinctions of thecalcareous nannofossils occur:Discoaster pentaradiatus andDiscoaster surculus.[7][5] TheGSSP for the Gelasian is located at the Monte Sant Nicola near Gela.
The top of the Gelasian is defined magnetostratigraphically as the end of the Olduvai (C2n) chronozone, and faunally as the extinction level of the calcareous nannofossilDiscoaster brouweri (base ofbiozone CN13). Above the Gelasian as the first occurrences of the calcareous nanofossilGephyrocapsa sp. and the extinction level of the planktonicforaminiferGlobigerinoides extremus[8][5]
During the Gelasian the ice sheets in theNorthern Hemisphere began to grow, which is seen as the beginning of theQuaternary ice age. Deep sea core samples have identified approximately 40marine isotope stages (MIS 103 – MIS 64) during the age. Thus, there have probably been about 20 glacial cycles of varying intensity during the Gelasian.
In the regional glacial history of theAlps, this age is now calledBiber. It corresponds toPre-Tegelen andTegelen in Northern Europe.[9]
During the Gelasian, theRed Crag Formation ofButley, the Newbourn Crag, theNorwich Crag Formation and theWeybourne Crag Formation (all fromEast Anglia, England) were deposited. The Gelasian is an equivalent of thePraetiglian andTiglian Stages as defined in theNetherlands, which are commonly used in northwestern Europe.
