Geoscience Reference
In-Depth Information
10
(a)
(b)
Figure 10.16 (a) White fragments of chalk in this soil are a conspicuous clue to the bedrock beneath. It is
always worth checking soil excavated by burrowing organisms (in this case prairie dogs at Whipsnade Zoo,
Bedfordshire, UK). Burrow is about 12 cm across. (b) A hand auger, useful for obtaining samples of the shallow
subsurface, including soil. The auger is lying alongside a loose 'core' of soil obtained from this locality. (a: Tom
W. Argles, The Open University, UK; b: Mark Brandon, The Open University, UK.)
Superfi cial deposits
Landforms commonly refl ect superfi cial deposits, which should
be noted on fi eld maps, especially where they mask the
bedrock. The extent to which you map the distribution of
different superfi cial deposits depends on the focus of the
mapping project; in some cases, mapping is specifi cally
targeted at Quaternary superfi cial deposits. Sand dunes, peat,
alluvium, laterite and beach deposits all represent a chapter in
the geological history of the area, and different projects may
focus on one or more of these deposits. Glacial and
fl uvioglacial deposits can form dramatic landscape features (e.g.
drumlins, eskers, terminal moraines, terraces), so you should
distinguish these from bedrock landforms where possible. A
few superfi cial deposits (e.g. landslides) can be positively
misleading. Large landslides may not be obvious at fi rst (Figure
10.17), and the jumbled structure could prove a puzzle. Clues
to landslides include: a prominent scar (commonly curved);
hummocky ground with a rather low average slope and small-
scale drainage, small ponds, etc.; a vegetation contrast between
the landslide debris and the surrounding undisturbed land.
Figure 10.17 Typical landslide
topography in Glacier National
Park, Montana. The landslide
material forms the hummocky
ground with patchy vegetation
sloping from the scree fans at the
base of the cliffs towards the level
plain in the foreground. (Courtesy
of the U.S. Geological Survey;
photographer P. Carrara.)
Wherever exposure is poor, take the opportunity to annotate
your fi eld map with any relevant information on topography,
superfi cial deposits, drainage, soils or vegetation. Figure 10.18
shows an example of a fi eld map drawn largely from the results
of numerous auger holes, combined with landscape features.
These observations will help corroborate your interpretation of
the underlying geology when drawing the fi nal map.
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