The Gelasian is in Earth's history, the lowest stratigraphic stage of the Pleistocene ( Quaternary ). Until 2006, it was regarded as the top level of the Pliocene. The Gelasian began geochronological before approximately 2.588 million years ago and ended about 1.806 million years and thus lasted about 782,000 years. The period before the Gelasian means Piacenzium and is attributed to the Pliocene. After the Early Pleistocene Gelasian began.
Naming and history
The eponymous locality for this stage is the city of Gela ( Caltanissetta Prov. ) in Sicily, Italy. The stage was proposed in 1994 by a group of Italian geoscientists (Domenico Rio, Rodolfo Sprovieri, Davide Castradori and Enrico Di Stefano ).
Definition and GSSP
The Gauss - Matuyama boundary marks a reversal of the geomagnetic field in front of around 2.588 million years. Here, the exact date of commencement of Gelasiums was fixed. At this boundary, the calcareous micro-organisms (protozoa ) Discoaster pentaradiatus and Discoaster surculus that were not found in the layers of the previous Piacenziums as nannofossils died out. The upper limit is the magnetic polarity chronozone C2n ( Olduvai ) and the calcareous nannoplankton Aussterbehorizont the -art Discoaster brouweri (base of Zone CN13 ). Just over the border is the Erstvorkommen the calcareous Nannofossilgattung Gephyrocapsa. and the Aussterbehorizont of planktonic foraminifera Globigerinoides extremus. The GSSP (global calibration point ) of the Gelasiums is located on the Italian Monte San Nicola near the Sicilian Gela.
Position of Gelasiums
The International Union for Quaternary Research ( INQUA International Union for Quaternary Research ), called in 2006 to the International Commission on Stratigraphy (ICS, International Stratigraphic Commission) to relocate the Gelasian from the Pliocene to the subsequent Pleistocene. In this way the Pleistocene may be extended and coincide its inception at the beginning of the Ice Age. This would be the starting point for a new establishment of the Quaternary, which would then again, as there are up to 2004, from the series Pleistocene and Holocene. In June 2009, the Executive Committee of the IUGS ratified the proposal, the Gelasian the Pleistocene and thus represent the Quaternary
In the Gelasian, at the beginning of the Pleistocene, polar caps of the earth began to freeze. This event marked the beginning of a new Ice Age, Ice Age of the Cenozoic ( Quaternary ), holding with its alternation of ice ages and warm periods until today.