Migration of Organic Molecules from Sediment to Fossils - Biopolymers: A Molecular Paleontology Approach - page 76

indicate that the site is 25.8 Mya, a result confi rmed by studying the fl oral assemblage
(Köhler 1997 ). Well preserved fossil insects, fi shes, mammals and amphibians have
been discovered together with land- derived plants and fruits (Lüniger and Schwark
2002 ). The oil shale was deposited in a complex maar-like structure in a tectonic gra-
ben (Lehmann 1930 ; Pirrung 1998 ). A basaltic fl ow from a nearby volcano terminated
the lake sequence by fi lling the lake basin and preserving the sediments (Schreiber
1995 ). We have chosen the EnspelLagerstätte as a study site because of the excep-
tional molecular preservation of the fossils. The insect cuticles have a partially ali-
phatic composition (Stankiewicz et al. 1997a ), and the high organic matter content
would favor contamination of fossil molecular signatures by sediment-derived ones if
such a migration occurred.
Three fossil samples were analysed: one dicotyledon (angiosperm, Fig. 4.1a ),
one conifer (gymnosperm, Fig. 4.1b ) and one weevil (Fig. 4.1c, d ) from Enspel
levels 8, 12 and 6 respectively. The dicotyledon leaf was used only to provide data
on molecular preservation and not for comparison with the enclosing sediment. The
fossil samples were released from the sediment mechanically using a scalpel under
a light microscope and any adhering sediment particle was carefully brushed away.
After this the samples were agitated in deionised water to facilitate density separa-
tion of the fossil and any residual sediment. Reagents were not applied during the
cleaning process to avoid chemical alteration. About 5 g of sediment were ground to
generate a homogeneous sample.
Portions of the posterior extremity of the abdomen of the weevil (Fig. 4.1c ) were
removed for electron microscopy prior to fragmentation of the remaining material
for chemical analysis. This enabled comparison to be made with similar samples
from a modern weevil. In the plants the specimens were fragmented and extracted,
and fragments were subsequently retrieved for microscopy. All sub-samples for
electron microscopy were cleaned in hydrochloric and hydrofl uoric acids to remove
mineral matter which would obscure the surfaces and prevent sectioning for micro-
scopic analyses.
For chemical analysis the fossils, and the separated associated matrices, were
transferred to glass vials and extracted ultrasonically with 2:1 dichloromethane/
methanol for 1 h. Each extracted residue was divided into two fractions for further
analysis.
Transmission (TEM) and scanning (SEM) electron microscopy were used to
determine the quality of morphological preservation. Pieces of fossils were taken
from the same samples as those used for chemical analysis and were demineralised
(see above) prior to EM study. In order to maximise the availability of material for
chemical analyses, especially from the tiny weevils (Fig. 4.1c ), only very small por-
tions of each fossil were studied. Details of methods are given in Collinson et al.
( 1998 ) and Stankiewicz et al. ( 1998a ) and references therein. Interpretations of
structure and organisation were informed by comparison with results previously
obtained for other modern and fossil leaves (Collinson et al. 1998 ; Gupta et al.
2007 ) and arthropods ( Stankiewicz et al. 1998a , b , c , 2000 ; Collinson and Briggs
unpublished).