25th International Meeting on Organic Geochemistry IMOG 2011

P-204
Are poriferan biomarkers preserved in the geological record? A
study on sponge fossils and sponge-rich sediments of various
ages
Juliane Germer, Martin Blumenberg, Joachim Reitner, Volker Thiel
Georg-August-University, Göttingen, Germany (corresponding author:jgermer@gwdg.de)
Sponges are considered to be the most ancient
metazoans. 14 fossilized sponges and sediments
containing abundant sponge remains were extracted
to test the preservation potential of four classes of
sponge-derived lipid biomarkers in the bitumen
fractions of geological samples (mid-chain branched
fatty acids, demospongic acids, sterols and
brominated secondary metabolites). Modern sponges
and sponge-microbial carbonate crusts were used as
reference materials.
The recent samples contain large amounts of midchain
branched fatty acids (MBFA) characterized by a
remarkable variety of structural isomers in the C16 to
C26 range. Specific, yet unknown sponge-associated
bacteria are suggested to be the producers of shortchain
MBFA (C16 – C19) which are subsequently
elongated by the sponge cells to long-chain MBFA [1].
Monomethylated mid-chain branched alkanes,
potential diagenetic derivatives of MBFA, occurred in
small amounts in some of the ancient samples
studied. These compounds showed, as well as the
MBFA, a great variety of structural isomers in the C16
– C20 range. Comparisons with the hydrocarbon
compositions of ancient carbonates and the fatty acid
and desulphurized hydrocarbon patterns of a recent
demosponge suggested that MBFA represent
plausible biological precursors of mid-chain branched
alkanes found in the ancient materials. However,
interpretations should be drawn with caution, since
other non-sponge sources may also account for midchain
branched alkanes in ancient sediments.
Long-chain demospongic acids (Δ 5,9 unsaturated,
≥C24) are widespread in members of the sponge
classes Demospongiae and Hexactinellida. However,
no plausible geological derivatives could be
recognized in ancient sponge-derived sediments,
suggesting that these compounds do not provide
suitable biomarkers for the contribution of spongederived
organic matter in the bitumen fractions of
ancient sediments.
Using MS/MS, the samples were carefully examined
for 24-isopropycholesterol and its geological
counterpart, 24-isopropylcholestane (24-ipc), whose
presence in ancient sediments and oils has been
proposed to record the first occurrence of metazoans
in the geological biomarker record [2][3]. However, no
24-ipc was detected in the ancient sponge-derived
samples.
Brominated organic compounds, potentially derived
from secondary metabolites, were observed as trace
compounds in the majority of the ancient samples
studied. These structures, however could not be
unambiguously assigned to biogenetic sources, but
may also be due to anthropogenic contamination,
which argues against an application of brominated
secondary compounds as sponge-derived
biomarkers.
Additionally, two methane-seep derived carbonates
containing ample sponge fossils were investigated for
their potential to preserve poriferan biomarkers under
conditions of early and rapid lithification. It was found
that signals from the microbial anaerobic oxidation of
methane were preserved remarkably well in these
seep carbonates, but again, no distinctive sponge
biomarkers were detected.
Summarizing, this study did not reveal a preservation
of sponge-cell derived biomarkers in the bitumen
fractions of ancient samples.
1. Pape, T., Lipidbiomarker
schwammassoziierter Bakterien und
Archaeen, in Institute of Biogeochemistry
and Marine Chemistry. 2003, University of
Hamburg: Hamburg. p. 164.
2. McCaffrey, M.A., et al., Paleoenvironmental
implications of novel C30 steranes in
Precambrian to Cenozoic age petroleum and
bitumen. Geochimica et Cosmochimica Acta,
1994. 58: p. 529-532.
3. Love, G.D., et al., Fossil steroids record the
appearance of Demospongiae during the
Cryogenian period. Nature, 2009. 457(7230):
p. 718-721.
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