Gelasium

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system series step ≈  age  ( mya )
quaternary Holocene Meghalayum 0
⬍
0.012
Northgrippium
Greenlandium
Pleistocene Young Pleistocene
(Tarantium) 		0.012
⬍
0.126
Middle Pleistocene
(Ionian) 		0.126
⬍
0.781
Calabrium 0.781
⬍
1.806
Gelasium 1,806
⬍
2,588
deeper deeper deeper older

The Gelasium is the lowest chronostratigraphic stage of the Pleistocene ( Quaternary ) in the history of the earth . Until 2006 it was considered the top level of the Pliocene . The Gelasian began geochronologically about 2.588 million years ago and ended about 1.806 million years ago and lasted about 782,000 years. The period before the Gelasium is called Piacenzium and is attributed to the Pliocene. After the gelasium, the calabrium began .

Naming and history

The eponymous locality for this level is the city of Gela (Prov. Caltanissetta ) 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 polarity reversal of the earth's magnetic field around 2.588 million years ago. Here the exact time of the beginning of the gelasia was set. At this border the calcareous microorganisms ( protozoa ) Discoaster pentaradiatus and Discoaster surculus , which were still found as nannofossils in the layers of the preceding Piacenzium , died out. The upper limit is the magnetic polarity chronozone C2n (Olduvai) and the extinction horizon of the calcareous nannoplankton species Discoaster brouweri (base of zone CN13). The first occurrence of the calcareous nannofossil genus Gephyrocapsa lies slightly above the border . and the extinction horizon of the planktonic foraminifera Globigerinoides extremus . The GSSP (global calibration point) of the Gelasium is located on the Italian Monte San Nicola near the Sicilian Gela .

Position of the gelasis

The International Union for Quaternary Research (INQUA, the International Union for Quaternary Research ) called for in 2006, the International Commission on Stratigraphy (ICS, International Stratigraphic Commission) on to move the Gelasian from the Pliocene to the Pleistocene below. In this way, the Pleistocene could be extended and its beginning coincident with the beginning of the Ice Age. This would then be the starting point for a new establishment of the Quaternary, which would then again consist of the Pleistocene and Holocene series , as it did until 2004 . In June 2009 the Executive Committee of the IUGS ratified the proposal to make the Gelasium a Pleistocene and thus a Quaternary.

meaning

In the Gelasian period, at the beginning of the Pleistocene, the Earth's Arctic polar cap began to freeze. This event marked the beginning of a new ice age , the Cenozoic Ice Age ( Quaternary ), which continues to this day with its alternation between cold and warm periods.

Individual evidence

  1. ↑ Open letter from the INQUA Executive Committee from 2006 ( Memento from January 7, 2010 in the Internet Archive )
  2. ↑ Philip L. Gibbard, Martin J. Head, Michael JC Walker: Formal ratification of the Quaternary System / Period and the Pleistocene Series / Epoch with a base at 2.58 Ma . In: Journal of Quaternary Science . tape 25 , no. 2 , February 2010, p. 96-102 , doi : 10.1002 / jqs.1338 .
  3. ^ D. Rio et al.: The Gelasian Stage (Upper Pliocene): A new unit of the global standard chronostratigraphic scale. In: Episodes. 21, 1998, pp. 82-87. (online, pdf)

literature

  • Felix Gradstein, Jim Ogg, Jim & Alan Smith: A Geologic timescale . Cambridge University Press 2004, ISBN 0-521-78673-8 .
  • Domenico Rio, Rodolfo Sprovieri, Davide Castradori, Enrico Di Stefano: The Gelasian Stage (Upper Pliocene): A new unit of the global standard chronostratigraphic scale. In: Episodes. 21/2, June 1998, pp. 82-87. (PDF) ( Memento from June 17, 2006 in the Internet Archive )

Web links