Geoscience Reference
In-Depth Information
Cadinane (XVII) is thought to derive from cadi-
nenes and cadinols which are ubiquitous in plants,
bryophytes and fungi (Bordoloi et al. 1989) and
from fragmentation of polycadinene resins (class
II) produced by angiosperms (van Aarssen et al.
1990). Cadinane is particularly present in gymnos-
perm (class I) resins (Simoneit 1986; Grimalt
et al. 1988). The dimers of cadinane, bicadinanes,
are often observed in oils. They are generated by
maturation of angiosperm (class II) resins (van
Aarssen et al. 1990; Stout 1995). Cadinanes are
therefore well-characterized higher plant bio-
markers which are often observed in Cretaceous
or younger sediments (van Aarssen et al. 1990).
So far, fully saturated cadinanes have not been
observed in Palaeozoic sediments.
However, their aromatic counterparts - cadal-
enes (XVII) - have been found in the extracts of
different coals of Carboniferous age (del R
´
o et al.
1994; Stefanova et al. 1995; Armstroff et al.
2006). Its earliest occurrence reported so far is
Visean (Armstroff et al. 2006) (Fig. 1).
to the different sedimentary settings (limnic in the
Ruhr v. paralic in the Saar). Changes in the penta-
cyclic terpenoids were also documented in these
coals (Vliex et al. 1994; Auras et al. 2006) (see
below). The presence of ent-beyerane, ent-kaurane
and phyllocladane in Lower Carboniferous sedi-
ments has led to the suggestion that a precursor of
the conifers already produced these compounds at
that time (Disnar & Harouna 1994). Since these
compounds do not occur in the Pinaceae, it has
been suggested that the Pinaceae separated early
from the other conifers (Armstroff et al. 2006),
implying that conifers had already evolved in the
Early Carboniferous.
Sheng et al. (1992) described an abundance of
tetracyclic diterpanes in Middle Devonian humic
coals from China. Among the identified compounds
are 17-norphyllocladanes, ent-beyerane and ent-
kaurane. This corresponds to the earliest reported
occurrence of ent-kaurane and ent-beyerane (Fig. 1).
Palaeobotanical data indicate that these Middle
Devonian coals mainly derive from pteridophytes
(Sheng et al. 1992). These are plants which, accord-
ing to the review of Alexander et al. (1987a), should
neither contain phyllocladane nor beyerane.
The absence of phyllocladane from the Middle
Devonian coals therefore appears consistent with
the absence of conifers during this period, while
the presence of ent-beyerane questions either the
origin of this compound in the Devonian coals or
its absence from pteridophytes (Sheng et al. 1992).
As far as we know, the oldest reported occurrence
of phyllocladane is Serpukhovian that is, late
Early Carboniferous (Fabianska et al. 2003; Izart
et al. 2006) (Fig. 1).
Totally or partially aromatized compounds
deriving from the tricyclic terpenoids are also fre-
quently reported in sediments. The most common
compounds are retene and simonellite (XXVI-
XXVII) which are thought to derive from the aro-
matization of abietane. However, Alexander et al.
(1987b) demonstrated in Miocene coals that retene
and simonellite are more likely derived from phyllo-
cladane and kaurane. Retene has been described in
the extracts of numerous Carboniferous coals (del
R´o et al. 1994; Stefanova et al. 1995; Fabianska
et al. 2003; Armstroff et al. 2006; Izart et al.
2006). Armstroff (2004) also describes the presence
of retene in Frasnian cannel coals from Russia. To
our knowledge, this is the earliest reported occur-
rence of retene which can be confidently associated
with a terrestrial origin (Fig. 1). If, as proposed by
Alexander et al. (1987b), retene from land plants
derives from aromatization of kaurane, its presence
in Devonian coals has no strong significance as
kaurane is mostly associated with Bryophyta and
Pteridophyta. Conversely, if it is demonstrated
that retene only derives from abietane or from
Diterpenoids. Particularly abundant among conifers
and their ambers are diterpenoids with abietane,
pimarane, kaurane and podocarpane (XVIII-XX)
skeletons. They are mostly produced by higher
plants, though some marine algae also synthesize
these compounds in a much functionalized form
(Simoneit 1986). According to the review of
Alexander (1987a), the different land plants can
be recognized from their specific diterpenoids con-
tribution. Bryophytes and pteridophytes differ
from gymnosperms by their absence of abietane,
beyerane and phyllocladane (XVIII, XXII, XXIII)
skeletons. The appearance of these latter compo-
unds in the sedimentary record could therefore
document the transition from 'horizontal' to 'verti-
cal' land plants. Phyllocladane, in particular,
would be a specific biomarker for conifers.
The occurrence of the fully saturated diterpe-
noids in Permian and Carboniferous coals is rela-
tively frequent (e.g. Noble et al. 1985; Schulze &
Michaelis 1990; Fleck et al. 2001; Fabianska et al.
2003; Piedad-S´nchez et al. 2004; Izart et al.
2006); phyllocladane, ent-beyerane and ent-kaurane
(XX-XXV) are often reported in particular. The
presence of phyllocladane and ent-beyerane in
these samples is consistent with the evolved flora
which existed in the Late Carboniferous.
The study of Schulze & Michaelis (1990) on
Carboniferous coals from Germany showed that
ent-kaurane is more abundant in the Westphalian
samples from the Ruhr, while ent-beyerane and
phyllocladane are more abundant in the West-
phalian and Stephanian coals from the Saar. The
authors proposed that this change might be due to
different inputs of higher plants, possibly related
