Geoscience Reference
In-Depth Information
5.4 Sampling strategies
Palaeontological sampling is aimed at determining the nature of
the population of fossil remains contained within a given suite
of sedimentary deposits, and from this to derive some
information about the ancient living population and
environment. Sampling strategies employed to achieve these
objectives must be at an appropriate resolution and carried out
effi ciently in order to provide valid data.
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5.4.1 Sampling for biostratigraphic or
evolutionary studies
For biostratigraphy and/or evolutionary studies a succession of
samples collected vertically through the deposit usually takes
precedence over investigating lateral variations (compare Figure
5.8a with 5.8b and 5.8c). Over geological time different fossils
are important for biostratigraphy (Figure A5.5). Many studies
incorporate more than one fossil group. In addition the
sampling strategy needs to be appropriate for the type of
biozonation that is used for the fossil group or period of
geological time (Figure A5.6). It is important with microfossils
to limit the risk of contamination (Chapter 13). The two types
of sampling are spot and continuous.
•
Spot sampling
can be performed at regular distance
intervals and/or targeted to different lithologies. The
advantage of spot sampling is that it is relatively quick and
minimizes the amount of material collected. Using this
technique, however, can easily miss small-scale or subtle
variations in deposition, as well as potentially important
non-visible events. As a general rule each lithology should
be sampled at several locations in order to determine if
there are any lateral, as well as vertical, variations in fossil
abundance and assemblage composition. The appropriate
(
(
(
Figure 5.8
Three different patterns of continuous or channel sampling.
(a) Overlapping samples parallel to bedding. (b) Repeat samples at right
angles to bedding within a lithology. (c) Samples at right angles to
bedding representing the stratigraphy, with short overlaps for cross-
correlation purposes.
