25th International Meeting on Organic Geochemistry IMOG 2011

P-453
Experimental palaeochemotaxonomy of conifers: the
Araucariaceae family
Yueming Lu, Yann Hautevelle, Raymond Michels
UMR7566 G2R, CNRS, Nancy Université, Vandoeuvre-lès-Nancy, France (corresponding
author:yueming.lu@g2r.uhp-nancy.fr)
Numerous studies of the molecular composition
of extant terrestrial plants pointed out the
chemotaxonomic value of a large assortment of
biological compounds. This means that these
biomolecules are synthesized by a restricted number
of taxa and can be used as specific biomarkers. Thus,
the distribution of vascular plant biomarkers
preserved in sedimentary material could serve as
proxy for terrestrial palaeoflora assessment.
Furthermore, as each flora is associated to more or
less precise climatic conditions, vascular plant
biomarkers may also serve as palaeoclimatic proxies.
However, our knowledge about
palaeochemotaxonomy of vascular plants is still
incomplete. Difficulties are related to 1) organic
diagenesis which may significantly modify the initial
molecular fingerprints; 2) the scarcity of well
preserved reference fossils; 3) the need to obtain a
collection of fossils covering all known species of
conifers. In order to help fill these gaps, we use an
experimental method based on artificial maturation of
extant plants by confined pyrolysis (Hautevelle et al.
2006). This technique allows to simulate conversion
of biomolecules into diagenetized compounds.
Within the 7 extant conifers families, we
investigated the palaeochemotaxonomy of
representatives of the Araucariaceae family. The aim
of this study are 1) to determine the
palaeochemotaxonomic signature common to all
Araucariaceae representatives, 2) to highlight the
molecular characteristics which should allow their
distinctions from other conifer families, 3) to evaluate
the inter- and intra-generic differences within the
Araucariaceae family.
12 species of Araucariaceae were selected.
They are well representative of the 3 extant genera:
Agathis (3 sp.), Araucaria (8 sp.) and Wollemia (1
sp.).
The result from GC-MS analysis shows that,
generally, the pyrolysates of Araucariaceae family are
characterized by a diversity of sesquiterpenoids and
diterpenoids. The sesquiterpanes are represented by
the cadalane group compounds (C15H18), bisabolane
isomers, and in some cases by farnesane. For the
aromatic sesquiterpenoids, the dominant compounds
are of the cadalene type (like calamenene, calamene
and cadalene), of the bisabolene type (like dihydro-arcurcumene)
and chamazulene. The distinction within
the different genera and species on the basis of the
sesquiterpenoids seems to be unlikely.
Concerning the aliphatic diterpenoids, all
families of Araucariaceae show a high abundance of
tetracyclic compounds, except those of Araucaria.
nemorosa and Agathis robusta. The tricyclic
compounds appear either alternatively to the
tetracyclic compounds, or sometimes co-exist (like
Araucaria bernieri, Araucaria bidwillii, Araucaria
laubenfelsii, Agathis australis). The bicyclic compound
like labdane is present in all species. Issues about the
significance of diterpenes are more complex because
of many unidentified compounds. Also tricyclic
compounds, like retene, 1,2,3,4-tetrahydroretene, 18-
and 19-norabieta-8,11,13-triene are common to all
species. Methyl-retene is also detected and shows a
relative lower abundance in some species.
Furthermore, the compounds having molecular mass
m/z 240 and 238 with a characteristic ion at m/z 169
and 168 respectively show a relative high abundance
in all species. No specific polar compounds could be
detected, except that of dehydroabietic acid.
The preliminary comparison of our results with
the occurrence of fossil Araucariaceae biomarkers are
in agreement with the few information described in the
literature: high abundance of tetracylic diterpanes and
lower abundance of tricyclic diterpanes. This feature
of Araucariaceae family could serve as a first criterion
to differentiate it from other conifer families.
Reference:
Hautevelle, Y., R. Michels, F. Lannuzel, F. Malartre,
and A. Trouiller (2006b), Confined pyrolysis of extant
land plants: A contribution to palaeochemotaxonomy,
Organic Geochemistry, 37(11), 1546-1561.
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