Microbioerosion - Trace Fossils as Indicators of Sedimentary Environments - page 212

In case a suitable vacuum chamber is not available, one can alternatively
apply the original cast-embedding technique as established by Golubic et al.
(1970) where a sequence of different resin/acetone mixtures is used to impreg-
nate and dehydrate the samples. The latter method is still important in neoich-
nological studies as the first step of the double-embedding technique ( Golubic
et al., 1970, 1975 ) allows the study of the embedded euendoliths within their
borings. Ultra-thin sectioning of these reembedded biological samples can fur-
ther be investigated with transmission electron microscopy for study of the
cellular structure.

2.3 Micro-CT
X-ray computed tomography (CT), and particularly micro-CT, is becoming an
increasingly popular 3D visualization tool for paleontological investigations of
various kinds (e.g., Dierick et al., 2007; Sutton, 2008 ). The highest resolution
is currently achieved with synchrotron microtomography that utilizes mono-
chromatic X-ray with very high beam intensity that allows a voxel size well
below 1 m—the spatial magnitude of microborings (e.g., Tafforeau et al.,

2006 ). But even conventional, more affordable, polychromatic X-ray micro-
CT is rapidly evolving and is about to enable resolutions at a submicron scale.
Related technologies worth mentioning are magnetic resonance imaging that
detects subtle differences in water or organic molecule content in fossils (e.g.,
Mietchen et al., 2008 ) and neutron tomography that utilizes a neutron beam
instead of X-ray and has advantages when visualizing organic fossil material
(e.g., Winkler, 2006 ).
The potential of all these technologies grounds on the fact that they are non-
destructive and have the ability to characterize sediment-filled fossil borings oth-
erwise inaccessible for the vacuum cast-embedding technique. Modern CT
scanners with sophisticated analysis software are able to detect very subtle den-
sity differences that are necessary to visualize lithified structures. For bioerosion
analyses, this has been exemplified by Beuck et al. (2008) with the establishment
of the macroboring ichnotaxon Osprioneides kampto within a Silurian stromato-
poroid, and by Tapanila (2008) who described the new microboring Pyroden-
drina cupra partly based on micro-CT scans of pyrite-filled fossil material.
The third major advantage of CT technology is to present results in printable
and/or screenable 3D formats such as colored semitransparent views
( Fig. 3 A), stereoscopic anaglyph techniques ( Fig. 3 B), or online supplementary
material as conventional or anaglyph 3Danimations (see, e.g., Beuck et al., 2007,
2008 , and http://app.pan.pl/acta53/app53-Beuck_etal_SOM.pdf ) .
As yet, CT application in bioerosion analysis is still anecdotal but the potential
for microbioerosion analysis with respect to 2D and 3D morphometry, drill-core
scanning, and the non-destructive study of well-lithified deep-time ichnocoenoses
is obvious.

m