25th International Meeting on Organic Geochemistry IMOG 2011

P-504
Hydrocarbons occurring in peats of different types and origins
(Southern Taiga of Western Siberia, Russia)
Olga Serebrennikova 1 , Yulia Preis 2 , Elena Gulaya 1
1 Institute of Petroleum Chemistry SB RAS, Tomsk, Russian Federation, 2 Institute for Monitoring of Climatic
and Geological Systems SB RAS, Tomsk, Russian Federation (corresponding author:gulaya@ipc.tsc.ru)
The compositions of n-alkanes, arenes and
terpenoids of peats, formed in forested herbaceous
tussock sedge swamp – sogra, two pine dwarf shrubs
sphagnum bogs – ryams and in two oligotrophic
floating mires located in the southern taiga of Western
Siberia, have been investigated.
A comparative analysis of hydrocarbon compositions
in peats formed under various conditions
demonstrated specific features characteristic of
individual peat types, which reflect their origin. But in
all peats other than sapropel, alkylbenzenes
consisted of two equal forms. These were benzenes
with a normal alkyl substituent and benzenes with a
substituent branched at the atom of the alkyl chain;
the latter were predominant in the majority of peats
but absent in sapropel. These benzenes with a
branched chain occurred in peats as three groups of
C17-C19 isomers different in the length of the alkyl
chain, in which a pentyl, butyl, propyl, ethyl, or methyl
group was attached at the exposition. In the majority
of peats, C19 isomers were predominant; C18
isoalkylbenzenes dominated in low-mire peat at a
depth of 200 cm. Benzenes with unbranched
substituents were mainly C15-C24 homologs with a
maximum concentration of C21. In sapropel, nalkylbenzenes
were C15-C21 homologues, whereas
they were absent in floating mire fuscum peat at a
depth of 200 cm.
The sogra low-mire peats differed from the others by
the occurrence of perylene among hydrocarbons,
higher concentrations of retene and intermediate
products of abietic acid transformation (saturated and
monoaromatic tricyclic terpenoids) and by the
absence of oleanene derivatives. Down the sogra
deposit profile, going from woody grass peat to grass
peat, the concentrations of bituminous components
and all hydrocarbon groups excepting tetracyclic
arenes (the concentration of which dramatically
decreased) increased. The relative concentration of nalkanes
in the mixture of hydrocarbons decreased;
the fraction of C15, C17, C21 and C25 homologues in nalkanes
increased. The ratio of hopanoids, which are
characteristic of bacteria, to tricyclic terpenoids
(gymnosperms are the main source) increased by a
factor of >20 to indicate an increased contribution of
bacterial biomass to the organic matter of peat at the
bottom of the peat deposit profile. The fraction of
unsaturated structures increased among pentacyclic
terpenoids, diploptene in particular. This suggests a
low diagenetic conversion of the organic matter of
peat, and it is consistent with a low degree of
diploptene decomposition. Among aromatic
hydrocarbons the perylene concentration
considerably increased. The concentrations of retene
and cadalene dramatically increased to suggest an
increased contribution of coniferous trees to the
formation of peat at this period of time.
The concentrations of bituminous components and
hydrocarbons in ryam raised bog fuscum peats
increased, as compared to those in sogra peats. In
the top portion of the peat deposit profile, C29 and C31
homologues were the main components of n-alkanes;
unsaturated hopane and oleanane precursors
dominated in the mixture of pentacyclic terpenoids;
diploptene was predominant. Among pentacyclic
terpenoids, the concentration of diploptene sharply
decreased and concentration of friedoolean-14-en,
which are characteristic of flowering plants, as well as
concentrations of cadalene and retene increased.
The floating mire deposit consisted of peats with considerably
different concentrations of bituminous components
and individual hydrocarbon groups. The distinctive
features of peats from this area were an
anomalously high concentration of pentacyclic
terpenoids in redeposited transitional peat and the
predominance of 17 (H),21 (H)-homohopane (22R)
among these terpenoids over the entire deposit
profile. The concentration of 17 (H),21 (H)homohopane
(22R)varied from 24% (sapropel and
redeposited peat) to 38-48% (fuscum peat) of the total
pentacyclic terpenoids basis. This can be a
consequence of a specific set of terpenoids in peatforming
plants or deposition conditions. The
unsaturated hopane and oleanane precursors, which
occur in living organisms and predominate in ryam
peats, occurred in floating mire peats in inferior
amounts. This was likely due to a rapid transfer of
biomass to anaerobic conditions because of a high
level of mire water in this area and the hydrogenation
of double bonds in biomolecules. The floating mire
peats were also characterized by a minimum cadalene
and oleanane precursors content (as compared
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