Gelasian
Encyclopedia
The Gelasian is an age in the international geologic timescale or a stage in chronostratigraphy
, being the earliest or lowest subdivision of the Quaternary
period/system and Pleistocene
epoch/series. It spans the time between 2.588 ± 0.005 Ma (million years ago) and 1.806 ± 0.005 Ma. It follows the Piacenzian
stage (part of the Pliocene
) and is followed by the Calabrian stage.
During the Gelasian the Red Crag
of Butley
and Newbourn and the Norwich and Weybourn Crags, all from East Anglia
(England) were deposited. The Gelasian is an equivalent of the Praetiglian and Tiglian stages as defined in the Netherlands
, which are commonly used in northwestern Europe.
city of Gela
in the south of the island. In 2009 it was moved from the Pliocene
to the Pleistocene
in order that the geologic time scale
be more consistent with the key changes in Earth's climate, oceans, and biota that occurred 2.588 million years ago.
The base of the Gelasian is defined magnetostratigraphically
as the base of the Matuyama (C2r) chronozone
(at the Gauss-Matuyama magnetostratigraphic boundary
), isotopic stage 103. Above this point there are notable extinctions of the calcareous nannofossils: Discoaster pentaradiatus and Discoaster surculus
. The GSSP
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 nannofossil Discoaster brouweri (base of biozone
CN13). Above the Gelasian as the first occurrences of the calcareous nannofossil Gephyrocapsa sp.
and the extinction level of the planktonic foraminifer Globigerinoides extremus.
During the Gelasian the ice sheets in the Northern Hemisphere
began to grow, which is seen as the beginning of the Quaternary ice age.
Chronostratigraphy
Chronostratigraphy is the branch of stratigraphy that studies the age of rock strata in relation to time.The ultimate aim of chronostratigraphy is to arrange the sequence of deposition and the time of deposition of all rocks within a geological region, and eventually, the entire geologic record of...
, being the earliest or lowest subdivision of the Quaternary
Quaternary
The Quaternary Period is the most recent of the three periods of the Cenozoic Era in the geologic time scale of the ICS. It follows the Neogene Period, spanning 2.588 ± 0.005 million years ago to the present...
period/system and Pleistocene
Pleistocene
The Pleistocene is the epoch from 2,588,000 to 11,700 years BP that spans the world's recent period of repeated glaciations. The name pleistocene is derived from the Greek and ....
epoch/series. It spans the time between 2.588 ± 0.005 Ma (million years ago) and 1.806 ± 0.005 Ma. It follows the Piacenzian
Piacenzian
The Piacenzian is in the international geologic timescale the upper stage or latest age of the Pliocene. It spans the time between 3.6 ± 0.005 Ma and 2.588 ± 0.005 Ma...
stage (part of the Pliocene
Pliocene
The Pliocene Epoch is the period in the geologic timescale that extends from 5.332 million to 2.588 million years before present. It is the second and youngest epoch of the Neogene Period in the Cenozoic Era. The Pliocene follows the Miocene Epoch and is followed by the Pleistocene Epoch...
) and is followed by the Calabrian stage.
During the Gelasian the Red Crag
Red Crag Formation
The Red Crag Formation is a series of marine deposits at the base of the Pleistocene in Suffolk and Essex. This material rests on an erosion surface of Cretaceous to Palaeogene rocks...
of Butley
Butley, Suffolk
Butley is a village and civil parish in the English county of Suffolk.Butley lies east of the town of Woodbridge on the B1084 road. Administratively, Butley forms part of the Suffolk Coastal district; from 1934 to 1974 it had been part of the former Deben Rural District.- External links :**...
and Newbourn and the Norwich and Weybourn Crags, all from East Anglia
East Anglia
East Anglia is a traditional name for a region of eastern England, named after an ancient Anglo-Saxon kingdom, the Kingdom of the East Angles. The Angles took their name from their homeland Angeln, in northern Germany. East Anglia initially consisted of Norfolk and Suffolk, but upon the marriage of...
(England) were deposited. The Gelasian is an equivalent of the Praetiglian and Tiglian stages as defined in the Netherlands
Netherlands
The Netherlands is a constituent country of the Kingdom of the Netherlands, located mainly in North-West Europe and with several islands in the Caribbean. Mainland Netherlands borders the North Sea to the north and west, Belgium to the south, and Germany to the east, and shares maritime borders...
, which are commonly used in northwestern Europe.
Definition
The Gelasian was introduced in the geologic timescale in 1998. It is named after the SicilianSicily
Sicily is a region of Italy, and is the largest island in the Mediterranean Sea. Along with the surrounding minor islands, it constitutes an autonomous region of Italy, the Regione Autonoma Siciliana Sicily has a rich and unique culture, especially with regard to the arts, music, literature,...
city of Gela
Gela
Gela is a town and comune in the province of Caltanissetta in the south of Sicily, Italy. The city is at about 84 kilometers distance from the city of Caltanissetta, on the Mediterranean Sea. The city has a larger population than the provincial capital, and ranks second in land area.Gela is an...
in the south of the island. In 2009 it was moved from the Pliocene
Pliocene
The Pliocene Epoch is the period in the geologic timescale that extends from 5.332 million to 2.588 million years before present. It is the second and youngest epoch of the Neogene Period in the Cenozoic Era. The Pliocene follows the Miocene Epoch and is followed by the Pleistocene Epoch...
to the Pleistocene
Pleistocene
The Pleistocene is the epoch from 2,588,000 to 11,700 years BP that spans the world's recent period of repeated glaciations. The name pleistocene is derived from the Greek and ....
in order that the geologic time scale
Geologic time scale
The geologic time scale provides a system of chronologic measurement relating stratigraphy to time that is used by geologists, paleontologists and other earth scientists to describe the timing and relationships between events that have occurred during the history of the Earth...
be more consistent with the key changes in Earth's climate, oceans, and biota that occurred 2.588 million years ago.
The base of the Gelasian is defined magnetostratigraphically
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...
as the base of the Matuyama (C2r) chronozone
Chronozone
A chronozone or chron is a slice of time that begins at a given identifiable event and ends at another. In the fossil record such tracer events are usually keyed to disappearance of a widely distributed and rapidly changing species or the appearance of such a species in the geological record...
(at the Gauss-Matuyama magnetostratigraphic boundary
Gauss-Matuyama reversal
The Gauss-Matuyama Reversal was a geologic event approximately 2.588 million years ago when the Earth's magnetic field underwent reversal.This event, which separates the Piacenzian from the Gelasian and marks the start of the Quaternary, is useful in dating sediments.-Biological effects:The event...
), isotopic stage 103. Above this point there are notable extinctions of the calcareous nannofossils: Discoaster pentaradiatus and Discoaster surculus
Discoaster
Discoaster is a genus of fossil haptophytes.- Species :Some species in this genus include:*D. asymmetricus Gartner*D. bellus Bukry and Percival*D. berggrenii Bukry*D. bollii Martini and Bramlette...
. The GSSP
Global Boundary Stratotype Section and Point
A Global Boundary Stratotype Section and Point, abbreviated GSSP, is an internationally agreed upon stratigraphic section which serves as the reference section for a particular boundary on the geologic time scale. The effort to define GSSPs is conducted by the International Commission on...
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 nannofossil Discoaster brouweri (base of biozone
Biozone
Biostratigraphic units or Biozones are intervals of geological strata that are defined on the basis of their characteristic fossil taxa....
CN13). Above the Gelasian as the first occurrences of the calcareous nannofossil Gephyrocapsa sp.
Gephyrocapsa
Gephyrocapsa is a genus of haptophytes.- Species :Species include:*G. caribbeanica*G. crassipons*G. ericsonii*G. kamptneri*G. muellerae*G. oceanica*G. ornata...
and the extinction level of the planktonic foraminifer Globigerinoides extremus.
During the Gelasian the ice sheets in the Northern Hemisphere
Northern Hemisphere
The Northern Hemisphere is the half of a planet that is north of its equator—the word hemisphere literally means “half sphere”. It is also that half of the celestial sphere north of the celestial equator...
began to grow, which is seen as the beginning of the Quaternary ice age.