Quaternary

Quaternary The Quaternary is the most recent geological period and system of rocks. It is part of the Cenozoic era and extends from 1.8 Ma ago to the present time. Its record is extremely varied, being influenced by large-scale climatic oscillations (glacial and interglacial in the higher latitudes, pluvial and interpluvial in the equatorial regions) and by the associated rapid changes of sea level. It is divided into the Holocene epoch, dating back to 0.01 Ma and the Pleistocene epoch from then to about 1.6 Ma ago. Nowadays we have abandoned the notion that the Quaternary represents a separate era following the Tertiary.

The term ‘Quaternary’ was first used by the French geologist Jules Desnoyers in 1829 to denote the most recent strata. In the following decade the Swiss geologist Louis Agassiz was able to demonstrate from erratic blocks and superficial deposits the previous (but geologically very recent) greater extent of the alpine glaciers. Similar evidence of post-Pliocene glaciation was soon gathered in lowland parts of Europe and North America to confirm the existence of an ice age not long ended. Then early in this century the succession of four Alpine glacial and interglacial deposits was described in the classic study by A. Penck and E. Bruckner. Subsequently, comparable phases in the North Sea region were discovered. In the meantime a fourfold glacial sequence had been recognized in North America. The several glacial phases now known in the southern hemisphere do not correlate exactly with those of the north.

Formal stratigraphic procedures are difficult to apply to the diverse continental and marine deposits of the Quaternary, but climatic criteria appear to be generally the most useful in global correlation. Magnetostratigraphic data also are locally helpful in this connection. From the original concept of four successive glaciations, interrupted by interglacial phases, in the northern hemisphere there has developed a far more complex schedule of climatic changes with attendant complicated stratigraphies.

This realization has come about from studies of the continuous record embodied in marine sediment cores, and of the oxygen isotope ratios of the included foraminifera. The succession of ratios appears to reflect changes in the global ice volume. Cores taken from the world's ice caps also reveal that the carbon dioxide content of the atmosphere has had an important influence upon the timing and intensity of glaciation. The task of reconciling the deep-sea record of climatic changes (perhaps twenty or more cold spells) with the half-dozen or so in the continental record is an urgent one for students of this part of the stratigraphic column. There is nothing to suggest that glacial conditions will not return to the middle latitudes in the near future, continuing the pattern of the past million years or more.

In recent years, there has been renewed interest in the work of the Serbian physicist M. Milankovich, who several decades ago postulated that cyclic changes in the Earth's orbital eccentricity, tilt, and precession are responsible for climatic oscillations. The critical periodicities are estimated as falling at 100 000, 40 000, and 19 000–20 000 years.

The climatic fluctuations have greatly affected biogeography. Mammals in particular evolved to meet the changes, but many suffered extinction. Human exploitation, at least in part, may be responsible for the disappearance of many of the larger animals. Human evolution has been the most distinctive biological feature of the Quaternary. The genus Homo, appearing first in Africa, spread rapidly into Eurasia during the early Pleistocene. Migration continued into Holocene time, accompanied by stone-based and more advanced cultures.

D. L. Dineley

Bibliography

Charlesworth, J. K. (1957) The Quaternary Era. 2 vols. Arnold, London.
Imbrie, J. and and Imbrie, K. P. (1979) Ice ages: solving the mystery. Macmillan, London.
Pomerol, C. (1982) The Cenozoic Era: Tertiary and Quaternary. (Trans. D. and and E. E. Humphries .) Ellis Horwood, Chichester.