Methodology and Techniques - Trace Fossils as Indicators of Sedimentary Environments - page 248

FIGURE 5 Minute trace fossils and their meiobenthic producers on a micritic bedding plane, Mid-
dle Triassic of Weimar, Germany (cf. Knaust, 2010b ). (A) Overview image made with the macro-
function of a digital camera. Diffuse sunlight illumination from the upper left augments the contrast.
(B) Microphotograph of a nematode (upper left) and its trail ( Cochlichnus isp.) taken with a digital
camera attached to the microscope.
Microorganisms (such as foraminifers and amoebas) are known to produce
traces that require a good microscope for their study. Bengtson and Rasmussen
(2009) used modern traces formed by large unicellular organisms such as amoe-
bas as an analog to explain Ediacaran trace-like fossils. Microscopy is com-
monly applied in the study of microborings, mainly in combination with
epoxy casting ( Ekdale et al., 1984; Wisshak, 2012 ).
A problem for unbiased ichnological studies of all size classes are those
trace fossils that fall between the microscopic and macroscopic domains. They
are typically in the range of their meiobenthic producers, for example, between
0.06 and 1 mm in shortest body size (e.g., platyhelminthes, nematodes, nemer-
teans, polychaetes, sipunculans, crustaceans, molluscs, etc.), and are often over-
looked because of their intermediary size. For instance, the Triassic shallow-
marine carbonates of Germany are rich in well-studied macrofossils, but the
comprehensive meiobenthic fauna including their trace fossils (partly concen-
trated in the fills of ammonoid shells) was only recently discovered ( Knaust,
2007 ). For the study of meiobenthic trace fossils, it often becomes necessary
to combine conventional microscopy with digital macrophotography in order
to capture a wider field of the object of investigation ( Knaust, 2010b ; Fig. 5 ).
Another application of microscopy is the study of burrow-internal details
such as grain alignment and orientation for the recognition of diagnostic fea-
tures. The morphological analysis of fecal pellets (microcoprolites) and the
internal structure of coprolites commonly requires a microscope ( Fl¨gel,
2004 ) as does the study of trace fossils in amber ( Poinar, 1998 ).
3.4 Scanning Electron Microscopy
Scanning electron microscopy (SEM) provides a useful means in ichnology and
is typically combined with other techniques, such as resin casting or thin sec-
tioning. Because of its high level of resolution, microscopical trace fossils or
trace-fossil parts can be studied in detail, for instance, microbial fossils within