Geoscience Reference
In-Depth Information
1972; Millay & Taylor 1977; Dunn et al.
2003). Although Pteridospermopsida emerge in the
Late Devonian, the representatives with resin
channels are from the Carboniferous. From this
perspective, resin production seems to have evol-
ved in the early gymnosperms. Analysis of the
molecular composition of resinite and amber
may therefore provide valuable information on
the evolution of gymnosperms and angiosperms
but is unlikely to elucidate the early evolution of
land plants.
Five chemical classes of ambers have been
recognized (Anderson & Crelling 1995). A large
majority of ambers is based on labdanoid diterpene
(X) polymers (Class I amber). Less abundant
are ambers based on cadinenes (XI) (sesquitere-
noids) polymers (Class II ambers) (Anderson et al.
1992; Anderson & Crelling 1995). Class III-V
resins are relatively anecdotic. While class I resins
derive both from gymnosperms and angiosperms,
class II resins only derive fromAngiosperms, in par-
ticular the Dipterocarpaceae (Anderson et al. 1992).
From this observation, the oldest resins and, in par-
ticular resinites from the Palaeozoic, should belong
to class I and derive from gymnosperms.
Amber or resinite samples older than the Cre-
taceous have often been studied by pyrolysis gas
chromatography mass spectrometry (py-GC-MS)
rather than by simple extraction. In the case of
recent to Cretaceous resinous material, the py-GS-
MS approach allows the successful identification
of the structure and the class of the resin to be
identified (Anderson et al. 1992; van Aarssen &
de Leeuw 1992; Anderson & Botto 1993). The
method has unfortunately proven much less success-
ful in the case of older ambers or resinites, because
most compounds liberated upon pyrolysis were
poorly informative.
In this way, Roghi et al. (2006) conclude that
Triassic ambers from Italy have an affinity with
class II or class I resins despite the fact that, due
to their age, it is unlikely that these resins are class
II. Similarly, the pyrolysates of Carboniferous resin-
like material, that is, resinites isolated from coals
(Crelling & Kruge 1998; Nip et al. 2009) and
resin rodlets of pteridosperms (van Bergen et al.
1995) are dominated by alkane-alkene doublets, as
well as alkylphenols and aromatics. This strongly
contrasts with the pyrolysates of Cretaceous or
younger resins. These results could reveal an
'unknown extinct type of resin' associated with
Carboniferous plants (van Bergen et al. 1995).
However, it seems highly plausible that, despite its
reputation of excellent chemical preservation,
amber also suffers from diagenetic aliphatization
similarly to other macromolecular compounds
(see below). As far as we know, no biomarker of
taxonomic interest has yet been extracted from
Palaeozoic resinites. Amber and resinite still have
to demonstrate their
suitability for
the study
of terrestrialization.
Elsewhere in plants (not only for plant resins),
most of signalling and warfare is the matter of
a large family of compounds: the terpenoids. The
smallest compounds (the monoterpenoids) are
highly volatile and therefore rarely preserved in
sediments, the major exception being in amber.
The terpenoids of higher molecular weight (referred
to as sesqui-, di- and tri-terpenoids) are frequently
observed in ambers and sediments.
Monoterpenoids. Monoterpenoids mostly corre-
spond to small odoriferous compounds incorporated
in amber. Original monoterpenoids or their prod-
ucts of diagenetic transformation can therefore be
observed. The extraction of amber frequently rele-
ases borneol, isoborneol and camphene (XII-XIV)
(Armstrong et al. 1996; Czechowski et al. 1996).
Monoterpenes found in amber could potentially be
of taxonomic interest for plants of carboniferous
or younger age, but not for the earliest plants (see
above). In addition, this process would require that
the plant which produced the resin is clearly
identified.
Sesquiterpenoids. Among the sesquiterpenoids,
eudesmane and cadinanes are the most important
for the study of terrestrialization. The eudesmane
skeleton (XV) is present in many terrestrial plants,
in particular angiosperms, but also in liverworts.
Although it has also been described in a few sponges
(Gross & K¨nig 2006), eudesmane is generally
considered as a marker of terrestrial origin for
petroleum and sediments (Philp 1994). Eudesmane
is absent from petroleum older than Devonian age
(Alexander et al. 1984), confirming its association
with non-flowering plants.
Often analysed with eudesmane is drimane (XV,
XVI) which, however, very likely has a bacterial
origin (Alexander et al. 1984) since it has been
observed in Palaeoproterozoic sediments (Dutkie-
wicz et al. 2007). The presence of eudesmane in
Palaeozoic coals is rarely reported. However,
Dzou et al. (1995) observed significant amounts of
eudesmane in Late Carboniferous coals from
Pennsylvania. Although its presence was questioned
by Borrego et al. (1999), eudesmane was also
reported by del Rio et al. (1994) in late Carbonifer-
ous oil shales from Spain. These are the earliest
reports of eudesmane in geological samples to our
knowledge (Fig. 1), although we might expect an
earlier appearance since this compound is present
in some liverworts (Toyota & Asakawa 1990).
The abundance of eudesmane in coal extracts
decreases as maturity increases (Dzou et al. 1995),
which might explain the rarity of reports of this
compound in Palaeozoic sediments so far.
