Geology Reference
In-Depth Information
Chapter 4
Migration of Organic Molecules
from Sediment to Fossils
Abstract
The 25 mya lacustrine deposit of Enspel, Germany, is important for
molecular taphonomy as weevils from this site have yielded the oldest preserved
traces of chitin. These weevil cuticles show excellent morphological and ultrastruc-
tural preservation. Plant cuticle is also preserved but it is obscured or distorted by
diatom impressions. Molecular analysis of dicotyledonous angiosperm leaf from
the Enspel deposit revealed the presence of polysaccharide, guaiacyl and syringyl
related lignin, and possibly degraded protein moieties in the insoluble macromo-
lecular component. Analysis of fossil conifer leaf showed the same moieties, but
syringyl related lignin units were absent. Py-GC/MS revealed C
9-33
n
-alkyl compo-
nents from both types of leaf, with C
13,14,29
homologues being the most abundant
n
-alkanes. TMAH pyrolysis yielded a fatty acid distribution ranging in carbon num-
ber from C
6-30
, with the C
16,18,14
components being the most abundant. Analysis of
fossil weevil cuticle also revealed the presence of an aliphatic polymer as evidenced
by C
9-33
n
-alkyl components in the pyrolysate and C
6-26
FAMEs (predominantly
even-numbered C
14-18
components) in the TMAH pyrolysate. Pyrolysates of the
sediments contain alkanes with distributions similar to those observed in the fossils;
however, TMAH pyrolysates of sediments were distinct from those of the fossils
with C
20-22
components being the most abundant in the conifer-bearing sediment
and the even-numbered C
22-26
components dominating in the weevil-bearing sedi-
ment. Thus, the aliphatic polymers in the fossils and sediment are different, appar-
ently comprised of moieties of different chain length. This suggests that the aliphatic
polymer in the plant and insect fossils is not derived from migration from the
organic-rich host sediment.
Keywords
TMAH pyrolysis Oligocene Chitin Aliphatic Diagenesis
Molecular preservation
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