25th International Meeting on Organic Geochemistry IMOG 2011

P-042
Search for chemotaxonomic indicator by analyses of resistant
macromolecules in plant fossils from the Cretaceous Futaba
Group, Japan
Kei Ikeda 1 , Ken Sawada 1 , Hideto Nakamura 1 , Masamichi Takahashi 2
1 Faculty of Science, Hokkaido University, Hokkaido, Japan, 2 Faculty of Science, Niigata University, Niigata,
Japan (corresponding author:ikedakei@mail.sci.hokudai.ac.jp)
Resistant macromolecules as cutin and suberin
constituting living plants are stable and have
resistance to microbial degradation and diagenesis.
The composition of molecular unit (monomer)
constituting resistant macromolecules are various
according to taxonomy. If variability of the
composition remained in plant fossils which had
undergone diagenesis, the composition can be
chemotaxonomic indicator, and it is useful for
classification. On the other hand, if the composition of
molecular unit constituting resistant macromolecules
changed according to environmrnt and diagenesis, it
can be indicator of paleoenvironment and mechanism
of diagenesis. However, it is unknown that what factor
affects the preservation of composition of molecular
unit. In this study, we analyzed resistant macromolecule
of a wide variety of plant fossils collected
from the same Cretaceous coal bed and investigated
variability of composition of their molecular units.
We analyzed mesofossils of angiosperms and
gymnosperms collected from Ashizawa Formation,
Futaba Group, Kamikitaba, northeastern Japan. For
example, fruit fossils of Hironoia fusiformis and
Archaefagacea futabensis, flower fossils of Esgueiria
futabensis, leaf fossils of Juniperus, a stem fossil of
Ephedra and some fossils of fruits, seeds and woods
which are uncertain about taxonomy. Extraction and
saponification were performed as reported previously
[1]. Briefly, powder samples of above fossils were
solvent-extracted under room temperature and 110°C
to be removed free compounds completely. The
residues were hydrolyzed by KOH / methanol under
room temperature and 110°C. GC-MS are used for
identification and quantification of compounds.
As main molecular units released from resistant
macromolecule of all samples, n-alkanoic acids (fatty
acids; C10-C28) and n-alkanols (C10-C28) were
detected. Distributions of carbon number of fatty acids
were clearly different according to a part of samples.
In woody fossils, the ratios of C14 /C16 released fatty
acids are low, while the ratio of C18 /C16 released fatty
acids are high. On the other hands, the C14 /C16 ratios
of released fatty acids are high and the C18 /C16 ratios
are low in non-woody organs such as cuticles (e.g.
flowers, fruits and leaves). These results indicate that
the woody and non-woody fossils reflect the
composition of suberin and cutin, respectively. As
Figure 1, the relationships between these ratios can
be distinguish non-woody fossils such as flower, fruit
and leaf from wood fossils. From these results, we
suggest that such diagram can be useful to identify
the kinds and parts of broken fossils. Also, by the
relationship between C20 /C18 ratios and C20 /C16
ratios of n-alkanols released from resistant
macromolecule, woody fossils can be separated from
flower, fruit and leaf fossils roughly. The high ratio of
n-C20alkanol may reflect the composition of suberin.
C18/C16
140
120
100
80
60
40
20
0
ester-bond FA
y = 1.78x + 29.78
0 10 20 30 40
C14/C16
angio-fruit
gymno-leaf
gymno-stem
gymno-seed
wood
系列6
線形 (系列6)
Fig. 1 Relationship between the ratios of C18 / C16 and
C14 / C16 fatty acids released from resistant macromolecules
in plant fossils. Line represents the
boundary between datasets of woody and non-woody
fossils based on the linear discriminant function.
Reference
[1] Sawada, K., Arai, T. and Tsukagoshi, M. (2008)
Organic Geochemistry 39, 919-923.
189