25th International Meeting on Organic Geochemistry IMOG 2011

P-229
Geochemical peculiarities of composition and structure of
heterocyclic components in bitumen extracts of organic matter
of lacustrine recent sediments
Lyubov Borisova 1 , Anatoliy Fomichev 2
1 Institute of Petroleum Geology and Geophysics SB RAS, Novosibirsk, Russian Federation, 2 Siberian
Research Institute of Geology, Geophysics and Mineral Resources, Novosibirsk, Russian Federation
(corresponding author:BorisovaLS@ipgg.nsc.ru)
Investigations of the composition and structure of
asphaltene components (AC) in the recent sediments
are not numerous [1, 2 and oth.]. This work is aimed
at revealing the peculiarities of the composition and
structure of AC in organic matter (OM) at the stage of
their initiation during diagenesis.
The subjects of inquiry are asphaltenes and
asphaltogene acids of OM from peats in the fields of
the Novosibirsk and Tomsk regions and sapropels
from the lakes of the Kulunda salt zone (West
Siberia). Lacustrine sediments are composed of siltsand,
sand-silt muds and sapropels. Extraction of
bitumen extracts of bottom sediments and AC was
performed according to the procedure developed by
V.P. Danilova [3 and oth.]. The composition and
structure of AC were examined by a complex of
physicochemical methods: elemental and x-ray
diffraction analyses, IR-, NMR-spectrometry, EPR,
and electron microscopy.
Based on data of elemental analysis, AC of
peats, as compared to AC of bottom sediments are
enriched in carbon, are depleted in hydrogen and
heteroatoms, and they have lower values of atomic
ratios H/C (1.7 – 1.9 against 1.8-2.0 for bottom
sediments). Asphaltogene acids relative to
asphaltenes for all samples are notable for the high
content of heteroelements and lower content of
hydrogen.
Based on the results of IR-, and NMRspectroscopy,
the structure of AC from OM of
diagenetic stage is characterized by a low degree of
aromaticity (averaging 0.2) as compared to AC from
OM of fossil sediments (0.5 – 0.8) [4 and oth.], high
carbon content in the long paraffin chains and
oxygen-containing groups. Aromatic structures are
represented by benzene. AC are almost identical and
by their structure resemble aliphatic esters and, to a
lesser extent, aromatic esters (of phthalate type).
EPR of AC from recent lacustrine sediments
indicates a low concentration of paramagnetic centers
(PMC) (10 15 pmc/g against 10 18 pmc/g for AC of OM
at the early stages of catagenesis [4]). A hyperfine
structure has been identified, which, judging from a
number of lines, is characteristic of copper linked with
4 atoms of nitrogen. A spectrum of tetravalent
vanadium (V +4 ) in AC of recent lacustrine sediments
has not been identified [4]. Spectroscopy results in
the visible region confirm the presence of copper
porphyrins and the absence of VO-porphyrins in AC
of recent lacustrine sediments. Previously, chlorines
have been identified in them by M.M. Gubina [5].
Based on x-ray diffraction data, AC of recent
lacustrine sediments show no crystal-like structure
(there are no clearly defined ordered hexagonal
structures), and they are composed of amorphous
mass. This is confirmed by electron microscopy: a
fibriform-lumpy structure is observed, representing the
onset of asphaltene initiation in diagenesis, while AC
of fossil sediments show a graphite-like structure.
Thus, during diagenesis, not asphaltenes proper
are produced, but only their precursors,
protoasphaltenes, less condensed compounds with
looser structure and higher content of
heteroelements. The chemical and supramolecular
structures of protoasphaltenes are predetermined by
the composition of the initial lipid-lipoid fraction of
living matter and are controlled by the geochemical
environment of accumulation in diagenesis.
References
[1] Galimov E..M., Kodina L.A. Investigation of organic
matter and gases in sedimentary strata of the World Ocean
bottom. – M.: Nauka. - 1982. - 288 p.
[2] Chernova, T.G., et al. (1974) Geokhimiya, N 8, 24-29.
[3] Kontorovich, A.E. (2004) Sketches of theory of naphthide
genesis (in Russian), SB RAS, Novosibirsk
[4] Borisova, L.S. (2004) Russian Geology and Geophysics
45, N 7, 884-894.
[5] Gubina, M.M. (1999) Organic geochemistry of oilgenerating
rocks of West Siberia (in Russian), IPG SB RAS,
Novosibirsk, 144-146.
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