Geology Reference
In-Depth Information
Chapter 1
Molecular Decay of Plant Biopolymers
Abstract
Analysis of modern
Metasequoia
leaves revealed the presence of
structural polyester cutin, guaiacyl lignin units and polysaccharides. Analysis of
environmentally decayed
Metasequoia
leaves revealed that guaiacyl lignin units
and cellulose were degraded more relative to vinyl phenol (the last being the
primary pyrolysis product of cutin and plant cuticles) suggesting that cutin is likely
more stable than lignin and cellulose during early diagenesis contrary to some
previous studies. This is supported by electron microscopy of changes in the
cellular structure and cuticle of the modern, decayed, and fossil
Metasequoia
leaves. Analysis of
Metasequoia
fossils from the Eocene of Republic (Washington
State) showed a signifi cant aliphatic component without detection of biopolymeric
lignin and polysaccharides. Fossils from the Eocene of Axel Heiberg revealed the
presence of lignin and an aliphatic polymer up to C
29
with cellulose and fossils
from the Miocene Clarkia deposit in Idaho of USA revealed lignin and an aliphatic
polymer up to C
27
without any polysaccharides. Modern
Metasequoia
needle was
heated experimentally in confi ned conditions that generated a macromolecular
composition with an aliphatic polymer up to C
32
and additional phenolic com-
pounds similar to those present in the fossils. Experimental heating of cutin is
known to generate an aliphatic polymer with carbon chain length <C
20
demonstrat-
ing that the
n
-alkyl component with carbon chain length >C
20
in the heated
Metasequoia
needle is a product of incorporation of longer chain plant waxes indi-
cated by the odd over even predominance of the >C
27
n
-alkanes. The resistant
nature of cutin compared to lignin and polysaccharides explains the ubiquitous
presence of an
n
-alkyl component (<C
20
) in fossil leaves even when polysaccha-
rides are absent and lignin has decayed.
Keywords
Lignin • Cellulose • Cutin • Mass spectrometry • Fossil • Preservation
