Migration of Organic Molecules from Sediment to Fossils - Biopolymers: A Molecular Paleontology Approach - page 78

Nguyen and Harvey 1998 ; Riou 1995 ; Schaefer et al. 1987 ; Tegelaar et al. 1989a , b ).
Thus, fl ash pyrolysis reveals bulk macromolecular information and it has been used
extensively in molecular characterisation of both modern and fossil plant material
(see van Bergen 1999 for review) and insects (Stankiewicz et al. 1997a , 1998a , b ).
The instrument parameters used in analyses here are listed in Gupta and Pancost
( 2004 ). Compounds were identifi ed using spectra reported in the literature (Ralph
and Hatfi eld 1991 ; Stankiewicz et al. 1997a , b , 1998a , b , 2000 ; Mösle et al. 1997 ,
1998 ; Bland et al. 1998 ; Gupta and Pancost 2004 ).
The second fraction of the extracted residue was prepared for thermochemolysis,
i.e. TMAH (tetramethylammonium hydroxide) assisted pyrolysis. This aliquot was
transferred to a fresh vial and 1 ml TMAH solution was added. The sample was
soaked in TMAH solution for 3-4 h prior to analysis to ensure that suffi cient TMAH
was available during on-line pyrolysis. TMAH-assisted pyrolysis helps to cleave
ester domains (McKinney et al. 1996 ; Almendros et al. 1998 , 1999 ) releasing the
constituent acyl moieties in the macromolecule as fatty acid methyl esters (FAME).
Instrumental parameters used were identical to those stated for normal pyrolysis.
Analytical Results
Ultrastructural Preservation of Fossils
Only parts of the dicotyledon (dicot) leaf could be seen on the hand specimen
(Fig. 4.1a ). The apex, base and most of the margin are missing or obscured. A main
vein is evident as a topographic high but venation detail is not evident. The fossil
conifer specimen is a portion of a branching leafy shoot with attached tiny scale-like
leaves (Fig. 4.1b ). This fossil thus includes tiny leaves and the stem within. In the
case of the broader parts of the specimen the stem may already have been woody if
secondary growth had occurred. SEM observation of fractured edges of the cleaned
specimens confi rms the preservation of a considerable thickness of organic material
and reveals probable cellular organisation (Fig. 4.2a ).
The plant surfaces are obscured almost entirely by impressions of diatoms
(Fig. 4.2a-h ). The diatoms are arranged randomly (Fig. 4.2b-d, g, h ) and have been
deeply impressed into the plant tissues (Fig. 4.2c-d, h ). The outlines are those of
pennate diatoms in which the raphe (axial groove) and also moulds of the rows of
pores aligned normal to the raphe (striae) are clearly evident (Fig. 4.2d, h ). The
small areas between diatoms, and the nature of the impressions (Fig. 4.2c-d, h ),
suggests that they were pressed into an originally continuous outer layer, consistent
with an original cuticle-covered leaf surface. However, the surface has been modi-
fi ed so strongly that it is not possible to confi rm the presence or absence of cuticle
from the SEM observations.
In a small area of one surface of the dicotyledon leaf rows of cell outlines are
evident, looking rather like rows of bricks in a wall (Fig. 4.2e, f ). These probably
represent the outer periclinal (parallel to surface) walls of the epidermal cells. Their