Organic Preservation of Biopolymers in Fossil Leaves - Biopolymers: A Molecular Paleontology Approach - page 47

(scanning a range of m/z 50-650; cycle time 0.6 s; ionisation energy 70 eV). Helium
was used as the carrier gas. The oven was programmed from 40 to 200 °C at
10 °C min −1 , then to 300 °C at 3 °C min −1 and held at this temperature for 20 min.
FTIR spectra were taken for the mid-IR range (400-6,000 cm −1 ) using a Nicolet
SX800 spectrometer fi tted with a Spectratec microscope. A KBrbeamsplitter with
either DTGS (bench) or MCT (microscope) detector and a glowbar ceramic source
were used to acquire 256 scans at a resolution of 4 cm −1 . For the microscope, masks
were used to generate a beam of 100 micron diameter which was used on selected
(thin) areas of the samples. For the pressed pellets (bench) the samples were ground
and mixed with 100 g of dried KBr in an approximate ratio of 2:100.
13 C NMR spectra were collected on a BrukerAvence 400 NMR spectrometer
operating at 100.62 MHz with a standard Bruker 4 mm CPMAS probe. The spectra
were collected using cross-polarisation (CP), magic-angle-spinning (MAS) at 6.5
KHz and a dipolar decoupling (ca 90 KHz). Typically around 12,000 scans were
collected with a cross polarisation time of 0.75 ms and a recycle delay of 3 s. The
chemical shifts were referenced with respect to tetramethylsilane (=0 ppm) using
solid adamantane as a secondary standard.
Microscopic Investigations
Gross Morphology
All leaf fossils (Fig. 3.2a, b , c, d) show a gross morphology which is distinctive
for each taxon. The overall leaf shape and leaf margin morphology is clearly
evident. In addition patterns of lighter and darker organic matter defi ne the presence
of main veins (darker) and patterns of topography defi ne the positions of lower rank
veins (thicker organic matter). Leaf morphology and venation pattern and both very
well-preserved.
Internal Organisation
A section through a small portion of the abaxial (lower) part of a modern Quercus
leaf (Fig. 3.3a ) is shown for comparison with fossil angiosperm leaves. The fossils
are represented by two different leaves of each of three angiosperm taxa; Populus
alba (Fig. 3.3b, c ), Castaneavesca (Fig. 3.3d, e ) one partial leaf of Pinus (Fig. 3.4 )
and Quercushispanica (Figs. 3.3f, g , and 3.5 ). In the angiosperms each section
(Fig. 3.3b-g ) spans the entire leaf thickness but which is the adaxial or abaxial sur-
face is not known. In the Pinus (Fig. 3.4 ) the upper edge is the outside of the leaf
which is covered by a thin fi lm of gold coating (thin dark line) as the same fragment
was used for SEM and TEM study. Only a portion of the Pinus leaf has been