Geology Reference
In-Depth Information
Methods
Fossil samples were carefully removed from host rock, crushed with a mortar and
pestle, and transferred to glass vials. They were then ultrasonicated in deionised
water for 10 min for three times to remove adhering rock. Following this, the sam-
ples were baked at 70 °C for 1 h to remove any residual water. Samples of euryp-
terid cuticle were then extracted ultrasonically three times, 15 min each with
2:1- CH
2
Cl
2
(DCM): CH
3
OH (methanol) to yield an insoluble residue. Thus, care
was taken to ensure that samples analysed were pure and without contamination that
might otherwise be adsorbed or absorbed to the organic matter (e.g. see Brocks
et al.
2003
). Residue was analysed by
in situ
Raman imagery to determine the nature
of the carbonaceous material and by Pyrolysis-Gas chromatography-mass spec-
trometry (Py-GC-MS) to reveal the molecular distribution of compounds. Selected
samples were analysed by thermochemolysis (pyrolysis in the presence of tetra-
methyl ammonium hydroxide (TMAH); de Leeuw and Baas
1993
) to permit struc-
tural analysis of the macromolecule and particularly ester moieties. Other samples
were hydrolysed in 1 M 95 % methanoic NaOH (saponifi cation) for 1 h at 70
°
C to
test the resistance of the macromolecule to base hydrolysis and then subjected to
thermochemolysis to determine the structure of the recalcitrant residue. Table
7.1
outlines the samples investigated and the specifi c techniques applied to them.
Cuticle was physically removed from modern specimens of
Pandinus imperator
and boiled in deionised water for 1 h to eliminate any residual epidermal tissue.
Cuticle was analysed from a molt of
Limulus polyphemus
. The modern samples
were analysed without solvent extraction in order to evaluate the entire molecular
distribution including the lipid moieties, which would be removed by solvent extrac-
tion. For discussion on lipid composition of arthropods see Howard and Blomquist
(
2005
), Stankiewicz et al. (
2000
). In contrast, the fossils were solvent extracted
prior to analysis to reveal the composition of the macromolecular organic matter by
removing soluble impurities. Raman imagery, pyrolysis, and thermochemolysis
were applied to samples of
Eurypteruslacustris
,
Pterygotusventricosus
and
P. sarlei
(Table
7.1
), and Raman imagery and pyrolysis were applied to
Eurypterusdekayi
.
Raman imagery was performed on an adelophthalmid and a scorpion from Joggins,
and a scorpion from the Lone Star Formation, a sample suite which had been sub-
jected to pyrolysis previously (Stankiewicz et al.
1998a
). The host sediment was
extracted in organic solvent (as described) and analysed with Py-GC-MS in order to
compare it with the composition of the eurypterids.
Flash pyrolysis involves the thermal fragmentation of the chemical constitu-
ents of a sample at high temperatures in an inert medium. These fragments are
then separated and identifi ed by GC-MS. Thus, fl ash pyrolysis (Py-GC-MS)
reveals bulk macromolecular information, and the method has been used exten-
sively in the molecular characterisation of insoluble fossil organic matter (Larter
and Horsfi eld
1993
; Logan et al.
1993
; van Bergen et al.
1995
; Stankiewicz et al.
1996
). Samples were analysed with a Perkin Elmer GC-MS. A CDS (Chemical
Data System) AS-2500 Pyroprobe pyrolysis unit was used with both the injector
and interface temperature at 290 °C. One hundred to 150 micrograms of
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