Molecular Decay of Plant Biopolymers - Biopolymers: A Molecular Paleontology Approach - page 11

a TD-GC-MS

C 18

o

o

o

o

o

o

C 2 N o

P3

C 29

o

P2

o o

o

P P1 o

o

py-GC-MS

b

X

odd over even predominance in n- alkanes

X

X C 27 C 29

X

X X

X X

P1

X

C 18

P2 C 32

P P3

B1

X X

X

X

B2 X

X

C 27

X

C 32

X X

X X X X

X X

X

Retention time

Fig. 1.7 Total ion chromatogram from ( a ) Thermodesorption (TD)-GC-MS analysis of experi-
mentally heated Modern Metasequoia leaf ( b ) py-GC-MS analysis matured modern Metasequoia
following thermodesorption of the same. C 2 N C 2 Napthalene, O n -alkanes. Other same symbols as
in Figs. 1.1 and 1.6

the fresh leaf tissue were not detected in the experimentally heated leaves, presumably
due to thermal transformation of these biopolymers during the experiment.
Structural biopolymers have been documented in morphologically well-preserved
Metasequoia leaves of Late Paleocene-Early Eocene age from the Ellesmere Island
(Canadian Arctic Archipelago), where they revealed the preservation of polysaccha-
rides and lignin and vinyl phenol (Yang 2005 ; Yang et al. 2005 ). Middle Eocene
leaves from the Axel Heiberg Island (Canadian Arctic Archipelago) analysed here
yielded lignin products similar to those identifi ed from the Ellesmere Island fossils,
with polysaccharide moieties (Yang et al. 2007 ; Jahren and Stenberg 2008 ).
Metasequoia leaves from the Miocene Clarkia site in Idaho, USA, in contrast, are
characterized by a dramatic reduction in polysaccharide moieties (Logan et al. 1993 ;
Yang et al. 2005 ). The fossils from the Eocene of Republic do not show any lignin or
polysaccharides but are composed of a macromolecular n -alkyl component. Such a
macromolecular aliphatic component is absent in the modern Metasequoia and hence
a product of diagenesis. Other important components of the fossil leaves released by
pyrolysis are pristenes. These isoprenoids are most likely are related to the pyrolysis
of tocopherol (Goosens et al. 1984 ; Höld et al. 2001 ). Indeed, fossil leaves display a
ubiquitous aliphatic composition, with little or no preservation of lignin and polysac-
charides, especially in fossils older than Cenozoic (see Table 2 in Gupta et al. 2006 ).
Cutan was not detected in the modern analogues of Metasequoia and cannot be the
source of the macromolecular aliphatics (Gupta et al. 2006 ; de Leeuw et al. 2006 ).
This gradation in the nature of biomolecular preservation in Metasequoia leaves is
paralleled by their morphological preservation as revealed by SEM (Yang et al. 2005 ).