25th International Meeting on Organic Geochemistry IMOG 2011

O-54
Biomarker and petrographic evidence for the origin and maturity
of perhydrous arctic coal and associated bitumen
Chris Marshall 1 , David Large 1 , Colin Snape 1 , Julius Babatunde 1 , Will Meredith 1 , Clement
Uguna 1 , Baruch Spiro 2 , Alv Orheim 3
1 University of Nottingham, Nottingham, United Kingdom, 2 Natural History Museum, London, United Kingdom,
3 GeoArktis As, Stavanger, Norway (corresponding author:colin.snape@nottingham.ac.uk)
Oil prone perhydrous coals are economically
important as oil source rocks and as targets for coal
liquefaction. Abundant perhydrous (>5.6% H dmmf
basis) coal deposits are preserved within the high
latitude, middle Palaeocene, Todalen Member of the
Central Tertiary Basin, Svalbard. Previous work
regarding the extent and characteristics of high
latitude perhydrous coals is limited. These coals
provide a significant opportunity to understand the
processes which controlled hydrogen rich coal
production during this period of unprecedented global
warmth.
This paper provides the initial findings from three
samples from the Svea and Longyear seams.
Hydropyrolysis-GCMS and coal maceral analysis
were used to determine the origin of the perhydrous
coal and associated bitumen in the Longyear and
Svea seams. Biomarker analysis was used to provide
insight into the depositional environments required to
form high latitude hydrogen rich coals at a time of
global warmth.
The principal findings of this study are;
� The Svalbard coals contain significant
amounts of fluorescent vitrinite and
detrovitrinite with low liptinite content (3-6%).
This implies perhydrous vitrinites are a
significant role in the oil potential of these
coals
� Comparison of hopane, sterane, n-alkane
and tricyclic diterpanes maturity and
biomarker ratios for the asphaltene and
kerogen phases indicates a terrestrial source
for the bitumen with no evidence of inmigration
from marine shales found deeper
within the basin. The Pr/nC17 ratio of the
maltene (free phase) is higher than that of
the bound asphaltene phase (4.5 vs. 0.1 in
the Longyear seam) which is likely to be
evidence of expulsion
� Unusually the Svalbard coals (figure 1)
contain extremely high concentrations of
hopanes (72,000ng/g C). These are
attributed to rapid biodegradation rates
caused by the unique climatic position of
Svalbard in the Palaeocene and preservation
by organo-sulphur compound formation.
The presence of 3-methylhopanes indicates
that significant methanotrophic bacterial
communities were present during coal
formation.
� It is proposed that seasonal control,
alongside coastal pH regulation and higher
temperatures/productivity of the early
Palaeocene, could allow optimal growth of
bacterial communities. This would provide all
the conditions required for preservation of
hydrogen rich, functionalised molecules
including bacterial hopanes. Organo-sulphur
molecule formation during early diagenesis
would explain the subsequent oil-rich,
vitrinite dominated nature of these coals.
� The extent of methantrophic communities
within the Svalbard coals may provide
evidence for increased terrestrial methane
cycling in the Paleocene Arctic much earlier
than previously reported at lower latitudes
((Pancost et al., 2007).
Figure 1 –TIC Chromatogram of the extracted free aliphatic
phase from the Longyear coal.
References
Pancost, R.D., Steart, D.S., Handley, L., Collinson, M.E.,
Hooker, J.J., Scott, A.C., Grassineau, N.V., Glasspool, I.J.,
2007. Increased terrestrial methane cycling at the
Palaeocene-Eocene thermal maximum. Nature 449, 332-+.
114