1. Structural, molecular and isotopic composition of organic fossils and their relationship to modern counterparts
Derek E.G. Briggs, Department of Geology and Geophysics, Yale University, P.O. Box , New Haven, CT 06520
The chemical changes that occur during fossilization provide a key to understanding the molecular transformation of biomolecules to geomolecules, and their contribution to sedimentary organic matter and kerogen.
Diagenetic alteration takes millions of years, but it is not known how soon it is initiated. Analysis of the cuticle of shrimp decayed in the laboratory for less than a year revealed the formation of an n-alkyl component with a chain length up to C24. Thus the first stage in the generation of the aliphatic rich composition of organic fossils involves the incorporation of labile lipids, such as fatty acids, during initial decay.
SEM images
showing loss
of exocuticle
after decay
Scales in
microns
Exocuticle
Analysis of Metasequoia leaves decayed in ponds revealed that lignin and cellulose are degraded relative to cutin. Fossil Metasequoia from the Eocene of Washington State lacked lignin and cellulose, but contained a significant aliphatic component up to C23. Cutin generates an aliphatic polymer < C20; the additional longer chain component may be derived from leaf waxes.
Vp:
from cutin
G1-G5:
from lignin
After decay,
loss of lignin
relative to cutin O
Comparison of the jaws of living squid and Nautilus with those of Cretaceous ammonites showed that their chitin-protein composition is transformed to aromatic compounds and an n-alkyl component up to C24 in fossils. Analysis (using thermally assisted methylation) revealed ether linkages and oxidative crosslinking, the first observed in animal fossils. O O
Ether and ester cross link in
fossil cephalopod jaw
Next we will apply spectroscopic and mass spectrometric methods to Tertiary fossils to refine our understanding of the biomolecular transformation of plant and animal components.