Environmental Engineering Reference
In-Depth Information
humid parts of the tropics there is evidence of fossil sand dunes (Figure 9.2). As well as
indicating previous aridity, they often provide information about wind directions and
constancy when the dunes were actively forming.
LITHOLOGICAL EVIDENCE
As well as the surface landforms, the subsurface sediments can sometimes allow an
interpretation of the environmental conditions under which they formed and indirectly
something about the climate at the time. In many cases this provides more information
and, hopefully, confirmation of the environment suggested by the landforms. The
sediment may be obtained from a surface exposure of material, suitably cleared to avoid
contamination, or it may be retrieved from depth by coring devices. Laboratory
examination of the physical and chemical properties of the sediments may then be
conducted to allow interpretations of environmental history. With such information,
glacial, fluvial, aeolian or marine sediments may be distinguished. Even where there are
no geomorphological features, there are many parts of temperate latitudes covered by
wind-blown sediments such as cover sands and loess (see Chapter 16). Analysis of some
of these thick sequences of loess shows they contain signs of cyclical climatic change,
with phases of loess accumulation interbedded with phases of soil accumulation during
the warmer stages. The aeolian sediment may also give an indication of wind direction.
Sediments can be preserved in a vast number of environments but much of their
palaeoclimatic value comes from the biological material they contain as the final type of
evidence.
Plate 9.3
Mammoth tusks exposed in a pit at Stanton
Harcourt, Oxfordshire.
Photo: M. D. Bateman.
BIOLOGICAL EVIDENCE
As part of the sedimentation process, biological material is frequently preserved with the
inorganic sediments and these provide a wealth of information about the environmental
