Geology Reference
In-Depth Information
11
Quaternary Periglacial
Conditions
Many of the high latitudes areas of North America and Eurasia that currently experi-
ence periglacial climates also experienced episodes of cold, non-glacial conditions
during the Quaternary. At the same time, extensive areas in the mid-latitudes of the
northern hemisphere that lay south of the continental ice sheets were also subject to
periods of intense cold. This chapter examines the evidence for Pleistocene periglacial
conditions in the high latitudes and the roles played by past permafrost and frost-action
processes in fashioning the mid-latitude landscapes.
11.1. INTRODUCTION
The Quaternary is the chronostratigraphic unit that refers to the last 2-3 million years.
At its lower boundary, it merges into the Late Pliocene. Some regard the Quaternary as
beginning as early as
∼
3.0 Ma, others take a paleomagnetic reversal at 2.6 Ma (Gauss) as
the cut-off.
Traditional, the Quaternary is divided into two units: fi rst, the Pleistocene, subdivided
into Early, Middle, and Late Pleistocene, and, second, the Holocene, the last 10 000 years,
that extends into today. Colloquially, the Quaternary is sometimes referred to as “The Ice
Ages” because the fl uctuating climates of the time enabled the growth and decay of con-
tinental ice sheets on many occasions.
The onset of growth of the Antarctic ice sheet began much earlier than the Quaternary,
possibly during the Late Miocene, approximately 10-13 million years ago. The reason for
this is still unclear. A contributing factor may have been related to the migration of the
Antarctic Plate towards its present polar position in Late Tertiary times, thereby allowing
a strong zonal westerly-wind circulation to develop across the entire southern latitudes,
effectively isolating the Antarctic continent.
11.2. THE TIME SCALE AND CLIMATIC FLUCTUATIONS
Changing oxygen-isotope ratios measured in the carbonate shells and skeletons of small
benthic and planktonic organisms (foraminifera) buried within deep-sea sediments
provide the best record of Quaternary climatic fl uctuations. This is because the tempera-
ture of the deep ocean has probably remained unchanged throughout the entire Pleis-
tocene and these bottom-living organisms incorporate oxygen
O
18
in direct
proportion to that contained in seawater. The composition of the latter can change and
O
16
and
δ
δ
