Geology Reference
In-Depth Information
For thermochemolysis samples were soaked in tetramethylammonium hydroxide
solution (TMAH) for an hour prior to pyrolysis. Samples were solvent extracted in
2:1—dichloromethane:methanol solution prior to analysis as necessary.
Results
The major pyrolysis products of modern fi sh scale (without lipid/solvent extraction)
(Fig.
11.2a
) included phenols, benzenes, indoles, pyrimidine, diketodipyrrole and
diketopiperazine derivatives (Table
11.1
). The abundance of diketodipyrrole, a
marker for hydroxyproline, is characteristic of collagen. Thermochemolysis of
modern fi sh scale (Fig.
11.2b
) revealed a distribution of fatty acyl moieties ranging
up to C
24
with an even over odd predominance; the shorter chain moieties, methylated
protein products and short chain acids, were diffi cult to detect. C
16
and C
18
saturated
and unsaturated components were the most abundant (see mass chromatogram
m/z
74 + 87).
EDX analysis of the fi sh scale (LH-50.081) showed that it is composed mainly
of Ca, P and O, indicating a preponderance of apatite. The composition of fi sh bone
(LH-50.085 and LH-50.087) is essentially the same. The surface of the fossil fi sh
scale displays linear ridges ~30-150
m across. The surface is granular and shows
no evidence of fi ner scale structure (not fi gured). The surface of the bone in speci-
men LH-50.087 (Fig.
11.3a, b
) similarly lacked structure but the bones of another
specimen (LH-50.085) (Fig.
11.3d, e
) showed negative impressions of coccoid, rod
shaped and some more elongate bacteria.
The eyes of fi sh may be preserved as an organic material (in which case this is the
only part of the fi sh preserved in this way) or as an authigenic mineral. EDX analysis
of the organic preservation (LH-50.087) showed that it consists mainly of C, O and
S, with some Ca. The eye is dark in colour with a blocky fragmented appearance
(Fig.
11.3a
). It is preserved as a microbial fi lm dominated by coccoids but with rare
rod shaped forms (Fig.
11.3c
). The mineralized preservation (LH-50.085) lacks C,
and is composed of Ca, O and Fe, indicating a diagenetic mineral, perhaps an iron
carbonate. It is pale orange in colour with a sugary texture under SEM (Fig.
11.3f
).
Samples of the fossil fi sh scale (Fig.
11.4
) were analysed by Py-GC-MS after
solvent extraction. No moieties diagnostic of protein (e.g., collagen) were detected
(Fig.
11.4a
). The fossil revealed largely an aliphatic polymer extending at least from
C
8
to C
21
with benzene and phenol derivatives, confi rmed by repeated analysis
(Fig.
11.4a
). Analysis revealed an unresolved complex mixture around alkane/
alkene homologue C
20
, possibly due to unresolved compounds; however, this was
not evident in repetitions of the analysis. Additionally, an unknown compound was
detected, not observed in any other fossil (Fig.
11.5
). Fatty acyl moieties released by
thermochemolysis of the same fossil range up to C
22
with an even over odd predomi-
nance (Fig.
11.4b
). The most abundant of these were C
16
and C
18
fatty acyl saturated
moieties as also seen in the modern fi sh scale (Fig.
11.2b
). Analysis of an isolated
μ
Search WWH ::
Custom Search