25th International Meeting on Organic Geochemistry IMOG 2011

P-328
Alteration of macromolecular composition of palynomorphs as
an effect of thermal maturation
Nadia al Sandouk 1 , Christoph Hartkopf-Fröder 3 , Stephan Kaufhold 2 , Jan Schwarzbauer 1
1 RWTH Aachen University, Aachen, Germany, 2 Federal Institute for Geosciences and Natural Resources,
Hannover, Germany, 3 Geological Survey of North Rhine Westphalia, Krefeld, Germany (corresponding
author:al_sandouk@lek.rwth-aachen.de)
To study thermal maturity of sediments
microscopic properties such as reflectance and color
of vitrinites and palynomophs are very important.
Because of their small size pure concentrates are
difficult to obtain and, hence, information on specific
chemical composition and structure is still very
limited. Therefore, alteration of the macromolecular
composition of palynomorphs during thermal
maturation is even nearly unexplored. Although many
pyrolytic studies are devoted to the composition of
modern and fossil sporopollenin the chemical
changes due to the maturation process have only
rarely been elucidated using pyrolysis methods.
The aim of this research was the comparison
of the analytical results get by different methods such
as µ-FTIR and Curie-Point-Pyrolysis. For this
suppose, sample material was taken from six
boreholes drilled at the southwestern rim of the Hils
Syncline (Lower Saxony Basin, NW-Germany). All
boreholes encounter the uppermost part of the
Pliensbachian, the complete Toarcian Posidonia
Shale and the lower part of the Aalenian. These
samples represent complete maturation series within
the oil window, meaning Vitrinite Reflectance from
0.48 % to 1.45 %. To release organic microfossils
from the sediment and for preparation of kerogen
concentrates several standard palynological
techniques have been followed using HCl and HF.
These acid treatments are believed not to influence
the chemical composition of palynomorphs [1].
Fig 1: µ-FTIR analysis of bisaccate pollen with
interpretation of the bands [2]
Bisaccate pollen, not separated from the
kerogen concentrates with different thermal
maturities, have been analyzed with µ-FTIR. As
Figure 1 shows, the contribution of methylene C-H
anti-symmetric stretch (γCH2-asym) as well as
methylene C-H symmetric stretch (γCH2-sym)
changes noticably, whereas the band representing
the C=C aromatic ring stretch remains roughly the
same. Also the bands describing the alcohol or alkylsubstituted
ethers C-O stretch (~1165-~1030 cm -1 ) or
the γC-H aromatic deformation (~970 - ~630 cm -1 )
show significant alterations.
These maturity-dependent changes are also
apparent in pyrograms, measured by Curie-Point-
Pyrolysis. Fig 2 shows a pyrogram from a bulk
kerogen sample with a thermal maturity of 0.48 % VR,
Fig.3 a sample with a maturity of 0,68 % VR.
Fig 2: Curie-Point-Pyrolysis of a bulk kerogen
concentrate, VR 0.48 %
Fig 3: Curie-Point-Pyrolysis of a bulk kerogen
concentrate, VR 0.68 %
This study clearly reveals systematic changes in
chemical structural properties of palynomorphs and
related kerogen concentrations with maturity.
References:
[1] van Bergen, P.F. 1999: Collection and storage of
fossil plant remains for organic geochemical analyses.
In Jones, T.P., Rowe N.P. (eds): Fossil Plants and
Spores:Modern Techniq2ues, 135-138. The
Geological Society, London
[2]Steemans, P., Lepot, K., Marshall C.P., Le Hérissé,
A., Javaus, e.J. 2010: FTIR characterization of the
chemical composition of Silurian miospores
(cryptospores and trilete spores) form Gotland,
Sweden. Review of Paleobotany and Palynology
461