Devensian Glaciation

Timeline of glaciation

There have been four major periods of glaciation in the Earth's past. The second, and possibly most severe, is estimated to have occurred from 850 Ma to 635 Ma (million years ago, in the late Proterozoic Age) and it has been suggested that it produced a "Snowball Earth" in which the earth iced over completely. It has been suggested also that the end of this cold period was responsible for the subsequent Cambrian Explosion, a time of rapid diversification of multicelled life during the Cambrian era. However, this theory is still controversial.

A minor series of glaciations occurred from 460 Ma to 430 Ma. There were extensive glaciations from 350 to 250 Ma. The current ice age, called the Quaternary glaciation, has seen more or less extensive glaciation on 40,000 and later, 100,000 year cycles. We are currently in an interglacial period, as the last glacial period ended about 10,000 years ago.

Major glacial periods in earth's history

Name	Period (Ma)	Period	Era
	30 - present	Neogene	Cenozoic
Karoo	360 - 260	Carboniferous and Permian	Paleozoic
Andean-Saharan	450 - 420	Ordovician and Silurian	Paleozoic
Cryogenian (or Sturtian-Varangian)	800 - 635	Cryogenian	Neoproterozoic
Huronian glaciation	2100 - 2400	Siderian and Rhyacian	Paleoproterozoic

Pleistocene glacial cycles

Originally, the periods were named after characteristic geological features, and these names varied from region to region. It is now more common to refer to periods by their marine isotopic stage number. The marine record preserves all the past glaciations; the land-based evidence is less complete because successive glaciations may wipe out evidence of their predecessors. Ice cores from continental ice accumulations also provide a complete record, but do not go as far back in time as marine data. Pollen data from lakes and bogs as well as loess profiles provided important land-based correlation data. The names system has not been completely filled out since the technical discussion moved to using marine isotopic stage numbers. For example, there are five Pleistocene glacial/interglacial cycles recorded in marine sediments during the last half million years, but only three classic interglacials were originally recognized on land during that period (Mindel, Riss and Würm).

Land-based evidence works acceptably well back as far as MIS 6, but it has been difficult to coordinate stages using just land-based evidence before that. Hence, the "names" system is incomplete and the land-based identifications of ice ages previous to that are somewhat conjectural. Nonetheless, land based data is essentially useful in discussing landforms, and correlating the known marine isotopic stage with them.

The last glacial and interglacial phases of the Pleistocene are named, from most recent to most distant, as follows. Dates shown are in thousand years before present.

Land-based chronology of Pleistocene glacial cycles

Backwards Glacial Index	Names					Inter/Glacial	Period (ka)	MIS	Epoch
Backwards Glacial Index	Alpine	N. American	N. European	Great Britain	S. American	Inter/Glacial	Period (ka)	MIS	Epoch
				Flandrian		interglacial	present – 12	1	Holocene
1^st	Würm	Wisconsin	Weichsel or Vistula	Devensian	Llanquihue	glacial period	12 – 110	2-4 & 5a-d	Pleistocene
	Riss-Würm	Sangamon	Eemian	Ipswichian		interglacial	110 – 130	5e
2^nd	Riss	Illinoian	Saale	Wolstonian or Gipping	Santa María	glacial period	130 – 200	6
	Mindel-Riss	Yarmouth	Holstein	Hoxnian		interglacial(s)	200 – 300/380	7,9,11
3^rd – 5^th	Mindel	Kansan	Elsterian	Anglian	Río Llico	glacial period(s)	300/380 – 455	8,10,12
	Günz-Mindel	Aftonian		Cromerian*		interglacial(s)	455 – 620	13-15
7^th	Günz	Nebraskan	Menapian	Beestonian	Caracol	glacial period	620 – 680	16

Older periods of the Pleistocene

Name	Inter/Glacial	Period (ka)	MIS	Epoch
Pastonian Stage	interglacial	600 – 800
Pre-Pastonian Stage	glacial period	800 – 1300
Bramertonian Stage	interglacial	1300 – 1550

**Table data is based on Gibbard Figure 22.1.

Ice core evidence of recent glaciation

Ice cores are used to obtain a high resolution record of recent glaciation. It confirms the chronology of the marine isotopic stages. Ice core data shows that the last 400,000 years have consisted of short interglacials (10,000 to 30,000 years) about as warm as the present alternated with much longer (70,000 to 90,000 years) glacials substantially colder than present. The new EPICA Antarctic ice core has revealed that between 400,000 and 780,000 years ago, interglacials occupied a considerably larger proportion of each glacial/interglacial cycle, but were not as warm as subsequent interglacials.

References

External Links

Aber, J.S., 2006, Regional Glaciation of Kansas and Nebraska. Emporia State University, Emporia, Kansas.
anonymous, 2000, Pre-Wisconsin Glaciation of Central North America. Work Group on Geospatial Analysis of Glaciated Environments (GAGE), INQUA Commission on Glaciation, Emporia State University, Emporia, Kansas.
anonymous, 2007, Global correlation tables for the Quaternary. Subcommission on Quaternary Stratigraphy, Department of Geography, University of Cambridge, Cambridge, England
Gibbard, P.L., S. Boreham, K.M. Cohen and A. Moscariello, 2007, Global chronostratigraphical correlation table for the last 2.7 million years v. 2007b., jpg version 844 KB. Subcommission on Quaternary Stratigraphy, Department of Geography, University of Cambridge, Cambridge, England
Hambrey, M.J., and W.B. Harland, eds., 1981. Earth's pre-Pleistocene glacial record. Cambridge University Press, 1004 + xv pp. (book downloadable as series of PDF files)
Silva, P.G. C. Zazo, T. Bardají, J. Baena, J. Lario y A. Rosas, 2007, Tabla Cronoestratigráfica del Cuaternario aequa., PDF version 1.4 MB. asociación española para el estudio del cuaternario (aequa), Departamento de Geología, Universidad de Alcalá Madrid, Spain. (Corelation chart of European Quaternary and cultural stages and fossils)