Gelasian
Earliest subdivision of the Quaternary Period
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Definition
The Gelasian was introduced in the geologic timescale in August 1996. It is named after the Sicilian city of Gela in the south of the island, with its GSSP being located near the city at Monte San Nicola. In 2009 it was moved from the Pliocene to the Pleistocene so that the geologic time scale would be more consistent with the key changes in Earth's climate, oceans, and biota that occurred 2.58 million years ago.
Magnetostratigraphically, the base of the Gelasian is defined as the base of the Matuyama (C2r) chronozone (at the Gauss-Matuyama magnetostratigraphic boundary), at isotopic stage 103. Above this line, notable extinctions of the calcareous nannofossils occur: Discoaster pentaradiatus and Discoaster surculus. Similarly, the top of the Gelasian is magnetostratigraphically defined 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 are the first occurrences of the calcareous nanofossil Gephyrocapsa sp., and the extinction level of the planktonic foraminifer Globigerinoides extremus.
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Climate
During the Gelasian the ice sheets in the Northern Hemisphere began to grow, which is seen as the beginning of the Quaternary ice age. Deep sea core samples have identified approximately 40 marine isotope stages (MIS 103 – MIS 64) during the age. Thus, there have probably been about 20 glacial cycles of varying intensity during the Gelasian.
Europe
In the regional glacial history of the Alps, this age is now called Biber. It corresponds to Pre-Tegelen and Tegelen in Northern Europe.
During the Gelasian, the Red Crag Formation of Butley, the Newbourn Crag, the Norwich Crag Formation and the Weybourne Crag Formation (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.