Page 127 - Sedimentology and Stratigraphy

8

Aeolian Environments

Aeolian sedimentary processes are those involving transport and deposition of material
by the wind. The whole of the surface of the globe is affected by the wind to varying
degrees, but aeolian deposits are only dominant in a relatively restricted range of
settings. The most obvious aeolian environments are the large sandy deserts in hot,
dry areas of continents, but there are significant accumulations of wind-borne material
associated with sandy beaches and periglacial sand flats. Almost all depositional envi-
ronments include a component of material that has been blown in as airborne dust,
including the deep marine environments, and thick accumulations of wind-blown dust
are known from Quaternary strata. Aeolian sands deposited in desert environments have
distinctive characteristics that range from the microscopic grain morphology to the scale
of cross-stratification. Recognition of these features provides important palaeoenviron-
mental information that can be used in subsurface exploration because aeolian sand-
stones are good hydrocarbon reservoirs and aquifers.

8.1 AEOLIAN TRANSPORT in air pressure between two places. Air masses move
from areas of high pressure towards areas of low pres-
The term aeolian (or eolian in North American sure, and the speed at which the air moves will be
usage) is used to describe the processes of transport determined by the pressure difference. The circulation
of fine sediment up to sand size by the wind, and of air in the atmosphere is ultimately driven by tem-
aeolian environments are those in which the depos- perature differences. The main contrast in temperature
its are made up mainly of wind-blown material. is between the Equator, which receives the most
energy from the Sun, and the poles, which receive
the least. Heat is transferred between these regions by
8.1.1 Global wind patterns air movement (as well as oceanic circulation). Hot air
at the Equator rises, while cold air at the poles sinks, so
The wind is a movement of air from one part of the the overall pattern is for a circulation cell to be set up
Earth’s surface to another and is driven by differences with the warm air from the Equator travelling at high